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35

STUDIES IN CONSERVATION 54 (2 009 ) PAGES 35–48

Received December 2007

The Effect of Ventilation, Filtration and

Passive Sorption on Indoor Air Qualityin Museum Storage Rooms

Morten Ryhl-Svendsen and Geo Clausen

INTRODUCTION

Large parts of the world’s cultural heritage collectionsare kept in storage. It is not unusual for only 10% ofa museum collection to be exhibited, and in the caseof archival collections nearly everything is usually instorage. When museum objects are exhibited thereare numerous compromises that must be made withregard to the control of the environment. For example,the room climate and air quality must be controlledfor the comfort of visitors and staff. In storage this isdifferent as there is not always a need for mechanicalventilation, at least not at the same rate required tofulfil the standard requirements for human comfort,and measures can be taken which primarily control airquality for preservation of materials. On the other hand,air pollutants present only in trace amounts, which are anegligible concern for people, may be very problematicfor materials because their impact (e.g. corrosion)accumulates over time. What at first seems like the simplesolution – to install full air conditioning with filtration

A study was conducted in five storage rooms at the National Museum of Denmark, in which the effect on indoor air qualityof mechanical ventilation, filtration and passive sorption was investigated. Mechanical ventilation and recirculation/filtrationwas initiated by introducing new ventilation and filtration units. Passive sorption was initiated by hanging sheets of sorptivematerials on walls. The control strategies were evaluated in terms of their ability to lower the concentration of internally generated

pollutants, and the indoor-to-outdoor concentration ratio of outdoor pollutants. The overall environmental impact for each methodwas evaluated by the use of material dosimeters. It was found that passive sorption performed better in a small room comparedto a large room. Mechanical ventilation and filtration with activated charcoal gave a high protection against ozone, but wereless effective in reducing nitrogen dioxide. Increased ventilation rates were expected to dilute internally generated pollutants, butambiguous results imply that the emission rate of organic acids may also vary. Recirculation/filtration was generally the mostefficient method. A cautious conclusion is that a combination of a low air exchange rate and internal recirculation with filtrationwill be most beneficial to the indoor air quality for such low-activity storage buildings.

units in museum storage buildings – is not that common,although properly functioning examples of such storage

facilities indeed exist. There are several reasons for this,including high installation and running costs or the useof alternative climate control systems that require lowair exchange rates (e.g. ‘passive’ climatizing). In the latterapproach, the focus has traditionally been placed ontemperature and relative humidity control rather than airpollution levels (e.g. [1]).

In this contribution the findings of an investigationof different air quality control strategies, from a fieldstudy carried out in the museum stores at the NationalMuseum of Denmark, are reported. Each locationinitially had no active air quality control (no mechanicalventilation). During this study the effect of different

modifications to the ventilation regimes, or the buildinginterior, were tested for their effect on the air qualityinside the storage areas. The reasons for choosing thedifferent control strategies are discussed below, but aboveall it must be mentioned that they all were chosen basedon the idea that the solutions should be compatiblewith the existing natural ventilation in the buildings.So, for example, a room was not simply fitted with an



36 M. RYHL-SVENDSEN AND G. CLAUSEN


over-sized ventilation system that in return for a highventilation rate would also require additional humiditycontrol.

Pollution pathways in buildings

The overall strategy that will best reduce pollution-induced deterioration is simply to avoid air pollutantsin the museum environment. While an ideal way to dothis is to locate a museum building away from traffic,industry and other polluting elements, and to constructthe building from materials that do not generate pollut-ants, it must be realized that most cultural heritageinstitutions face an array of local external and internalpollution sources. Instead, these are normally dealt withby blocking or removing the pollutants before they reachobjects in the collection. This can be done by using air-

cleaning filtration media in ventilation systems, or simplyby retarding the natural infiltration of polluted air.

In a building with both outdoor and indoor pollutionsources, the strategies chosen to tackle one type ofpollution may intensify problems with other pollutants.When outdoor pollutants (e.g. ozone) infiltrate abuilding, the pollutant will continuously be reducedin concentration as the pollutant reacts with surfacesover which the air passes. A reactive outdoor pollutantwill, therefore, usually be found in lower concentrationsindoors than outdoors, at a ratio dependent on the airexchange rate, the geometry of the room or building,and the reactivity between the pollutant and the indoor

surfaces. However, if at the same time other pollutants areemitted indoors (e.g. from building materials), then a lowair exchange, while reducing the indoor concentrationof a reactive outdoor pollutant such as ozone, will allowthe concentration of pollutants originating indoors tobuild up. Either scenario may be described by a simplemass balance model, assuming steady-state conditions(see also [2]):

S n

V

G

S n

nO I

+

++×

=

(1)

where I = indoor concentration of pollutant (ppb orµg·m−3); O = outdoor concentration of pollutant (ppbor µg·m−3); n = air exchange rate (hour −1); S = surfaceremoval rate (hour −1); G = generation rate of pollutant(ppb per hour or µg per hour); and V = volume of room(m3).

The first term on the right-hand side of the equationrepresents the net contribution of a pollutant enteringfrom outdoors, and the second term the indoor genera-

tion. The surface removal rate is defined as the insidesurface-to-volume ratio of a room or building multipliedby the ‘deposition velocity’ (a mass transfer coefficient).The surface removal rate has the unit of reciprocal time(hours in this case), and is directly comparable to airexchange rate. In a room with a surface removal rate of 1hour −1 the pollutants are removed from the air by surfacereactions at a rate equivalent to ventilation at a rate ofone air exchange per hour.

While outdoor air pollution infiltration is retarded bya low air exchange, pollutants generated indoors needa high air exchange rate to dilute them. In both casesthe overall air quality will be improved if the surfaceremoval rate is high. This can be achieved ‘passively’ by

introducing more highly sorptive surfaces in the room(e.g. wall coverings), or ‘actively’ by forcing the airthrough filters using mechanical ventilation.

For situations where pollutants generated bothindoors and outdoors are present, a combined solutionof a high ventilation rate using clean (filtered) outdoorair seems ideal. However, as climate control usually hasa high priority in collection areas, where the aim is tokeep conditions as stable as possible, a low air exchangerate combined with a high degree of filtration of theinternal air (using a recirculating filter unit or the like)offers a satisfactory alternative to mechanical ventilationwith outdoor air. Deliberate use of ‘passive’ filtration,

by increasing the area of sorptive surfaces in a room,has received little attention in the conservation field todate. The technique is frequently used for display cases,archival boxes or film cans, in which sorptive media areplaced for pollution removal [3]. However, studies fromthe human comfort field suggest that the use of sorptiveinterior surfaces positively influence the perceived airquality in a room [4].

Pollution control strategies

In this study, three control strategies for reducing airpollution were chosen, based on the outcomes predicted

from the pollution mass-balance in Equation 1:

1 Use of sorptive surface materials (passive sorption). Byadding extra, highly sorptive wall coverings to aroom, the surface removal rate should be increased.This should be equally effective for pollutantsgenerated both indoors and outdoors.



EFFECT OF VENTILATION, FILTRATION AND PASSIVE SORPTION ON INDOOR AIR QUALITY IN MUSEUM STORAGE 37


2 Mechanical ventilation with filtered outdoor air. Pollutantsgenerated indoors should be removed by ventilationwith new, outdoor air. To prevent the concomitant

infiltration of outdoor pollutants this air should befiltered.3 Recirculation and filtration of room air. Internal pollutants

are removed by mechanical air recirculation witha fan and filters. Such systems can be mobilestand-alone units, or integrated into a building’sventilation system. Recirculation allows the outdoorair exchange to be kept low.

By keeping the air exchange rate low it is expected thatthe infiltration of reactive outdoor pollutants will beminimal, but pollutants generated indoors may buildup in high concentrations. This was the situation in thestorage rooms prior to this study (the ‘baseline’), as they

were generally kept rather airtight, and contained a largeamount of potentially emissive materials, such as wood.

Success criteria for control strategies

A successful intervention should cause the level of airpollution to be lowered. It is broadly agreed that thekey air pollutants that cause adverse effects to materialsare ozone, nitrogen dioxide, sulphur dioxide, hydrogensulphide, organic acids (especially formic and aceticacids) and fine particles [5–10]. With the exception ofsulphur dioxide (which is present today only at verylow concentrations – often below the detection limit

indoors) these compounds were monitored in this study.Ozone and nitrogen dioxide originate almost entirelyfrom outdoor sources, hydrogen sulphide derives fromboth outdoor and indoor sources and organic acidsat any significant level are solely generated indoors.Particles may have both outdoor and indoor sources, buttheir chemical composition may vary with their sources.

As material damage is a key issue for the preservationof museum collections, the aggressiveness of the air canbe quantified by the use of material dosimeters, see forexample [11, 12]. Susceptible material samples give adirect indication of the combined impact of the variousair quality factors through the rate of damage to the

sample. Corrosion is an example of one such deteriora-tion process, which is influenced not just by oneenvironmental factor, but may be accelerated by severalfactors at the same time (e.g. air pollutants and climate).

The success criteria for the interventions were:

• a decrease in the concentration of pollutants gen-erated indoors;

• a decrease in the infiltration of outdoor pollutants,quantified as the indoor-to-outdoor concentrationratio (I/O); and

• a decrease in material dosimeter responses.For each criterion, the observed changes were evaluatedin relation to measurements performed under ‘nointervention’ conditions, as an initial baseline test carriedout in the same location, or as baseline tests carried outsimultaneously in a reference room.

The reasoning for choosing I/O ratio to evaluatethe outdoor pollutants rather than the concentrationwas that there may be large ambient concentrationvariations over the seasons; for example, ozone levelswill be much higher during summer than dur ing winter,and that alone will affect the indoor concentration.However, the I/O ratio for a building will generally

be maintained regardless of the variations in absoluteoutdoor concentration. The I/O ratio reflects the natureof the building and its operation, and any increase ordecrease in I/O ratio will reveal how well an inter-vention succeeds in excluding external pollutants.

METHOD

Five rooms within the museum’s storage facility werechosen for this study. The facility is housed in an oldindustrial building complex located in the suburban areaØrholm, north of Copenhagen.

The study took place between March and October

2006. The rooms were uniform with regard to airtightness(low exchange rates, generally <0.3 per hour), size (fourrooms had volumes of 130–170 m3, while the fifth wasapproximately 500 m3), and interior surface-to-volumeratio (generally 3–5 m2·m−3, including the projectingsurface area of the collection items). The rooms differed,however, in material composition of the collections.Henceforward the rooms will be referred to as Rooms Ato E; their properties are summarized in Table 1.

Baseline measurements

All tests periods were three months (12 weeks). All

locations were first monitored for one full period ‘asis’, before any changes were made to the rooms. These‘baseline’ measurements laid the ground for evaluatingthe possible effect of the subsequent interventions.This was done by comparing the percentage changebetween the baseline measurements and those madeduring the different interventions. An additional storageroom was monitored as a reference, in parallel with





both the baseline measurements, and while the differentinterventions were being tested in the neighbouring

rooms. This parallel baseline test made it possible toevaluate the relative effect each intervention made to theair quality of a room compared to the baseline variationsin the reference room. All the tests were performedover two successive three-month periods, both outsidethe heating season, at times when the indoor climaterequired least regulation. However, some variationmust always be expected over the course of the year,mainly due to variations in the weather. For example,the infiltration of outdoors pollutants may change if theseasonal wind pattern changes, or increased periods ofrain may raise the local relative humidity. In order to takeinto account such baseline variations when evaluating

the effect of an intervention, the change relative tothe reference room was measured and reported. If,for example, the concentration of a pollutant in thereference room increased by 20% between the twomonitoring periods, but at the same time only increasedby 4% in a room where some intervention took place,then the change in concentration at the location withthe intervention was (1.04/1.20) = 0.87 relative to thereference room, or 13% less change.

The change caused by an intervention relative to thereference room can be calculated:

(2)

where IVbefore

and IVafter

are the conditions in a roombefore and during an intervention, and REF

before and

REFafter

are the conditions in the reference room at thesame time.

Interventions

Passive sorption was initiated by installing sheets ofsorptive wall coverings. The sorptive material was anactivated charcoal (Semia) embedded in a non-wovenpolyester filament sheet. This product is hung on wallsto remove odours and vapours given off by constructionmaterials in newly-built homes. The product waspurchased in rolls 1 m wide, and cut into sheets thatcould be hung on walls, or fitted on the top or side ofshelves and other surfaces. Semia was used in one largeand one small room (Tables 1 and 2).

For mechanical recirculation/filtration of the air, amobile stand-alone filter unit was used in one room

(Kemfilter Maximus 700). The unit consisted of a fanand a filter pack with particle (HEPA grade) and gaseous(a combination of activated charcoal and potassiumpermanganate) filter media.

Increased ventilation with outdoor air was achievedin one room by the installation of a fan and air intake ina window frame, which forced the outdoor air througha combined particle (grade EU7) and gaseous filterwith activated charcoal impregnated cloth (Camfil FarrCityCarb). The system carried the new air via flexibletubes through a board partition into the storage roomwhere it was delivered into the middle of the room. Theused air exited the building through an air outlet located

away from the air intake. The risk of seriously affectingthe indoor climate by uncontrolled moisture inflow wasminimized by ensuring that the ventilation rate neverexceeded one air change per hour.

The interventions made in each room are listed inTable 2. This table contains details of the equipment usedand the physical property changes that were measured ineach room during the different interventions (variationsin air exchange rate, etc.).

Air qual ity monitor ing

Passive sampling was used to measure the average

concentration of gaseous air pollutants. The pollutantconcentrations reported, or the I/O ratios based onpollutant measurements, are averages of three months,derived from two 6-week sampling periods. Ozone,nitrogen dioxide, and hydrogen sulphide were measuredusing the Analyst diffusive sampler system, providedand subsequently analysed by the Italian Institute forAtmospheric Pollution (CNR-IIA) [13, 14]. Organic

Table 1 Physical properties of the storage rooms tested in this study

Location Collection items Volume (m3 ) Surface area

including

collection (m2 )

Room A Archaeological objects, mainly

pottery

503 1960

Room B Contemporary objects: wood,

metals, textile, ceramics, plastics

130 622

Room C Furniture, books 171 499

Room D Contemporary objects: wood,


165 449

Room E Contemporary objects: wood,


130 688

%1001

REF

REF

IV

IV

(%)changeRelative

before

after

before

after

�





acids (formic plus acetic) were measured using Palme’sdiffusion tubes provided and subsequently analysed byOxford Brookes University, UK [15]. Volatile organiccompounds (VOCs) were sampled in Room B. Thesemeasurements were made by short-term active samplingfor 40 minutes, during which a pump drew 6 L of airthrough a tube that contained an adsorbing material(Tenax). In contrast to the passive sampling, these activesamples gave instantaneous concentration values ratherthan long-term averages. The Tenax tubes and theirsubsequent analyses were provided by the FraunhoferWilhelm-Klauditz-Institut in Germany.

Particle pollution was measured as the concentrationof ultrafine particle suspended in air (0.02–1.0 µmdiameter) and as the deposition of coarse particles(‘dust’: >2.0 µm diameter) on horizontal surfaces.For the measurements of concentration in air, P-Trakcondensation particle counters were used. Particlecounts were taken once per minute during the samplingperiod, which typically lasted six to eight hours.

Dust deposition was measured on cleaned horizontalsurfaces (glazed tiles), which were exposed for threemonths. The accumulated deposition was sampled usinga sticky dust-lifter gel (BVDA environmental gel), whichwas then examined at 40× magnification. The amount

of dust deposition (percentage of surface area coveredby particles) was determined from digital analysis ofmicroscope images (Image J software).

The air exchange rates of the rooms investigatedwere determined by measuring the concentrationdecay rate of a tracer gas [16]. The gas (Freon 134a)was released into the room under investigation, andthe air was continuously mixed during measurement

using electric fans. The concentration of tracer gas wasmeasured at one-minute intervals using a photo-acousticspectrometer (Innova Multigas Monitor 1302). Thetemperature and relative humidity of the air at all siteswas monitored using electronic sensors connected todata loggers, which recorded the climate at one-hourintervals (Tiny Tag data loggers and IPI preservationenvironment monitors).

Dosimetry

The corrosivity of air was assessed using pure silver

coupons (Purafil ERC) and the rate of atmosphericcorrosion was expressed by the development in corrosionlayer thickness [11, 12]. Lead was also used to determinethe corrosivity of air; pure lead coupons were preparedfollowing the methodology of ISO 11844-2 [17]. Therate of atmospheric lead corrosion was assessed bydetermining the corrosion mass after exposure. This wasachieved by weighing the coupons on a microbalance,after stripping them of corrosion products by immersionin 20% hydrochloric acid followed by rinsing in distilledwater. The mass values obtained were compared to themass of the coupons prior to exposure, to yield the netmass loss to cor rosion products [18].

The rate of oxidation caused by ozone was estimatedfrom measurements of the surface deterioration ofstretched samples of natural rubber (latex dosimeters).After exposure the dosimeters were analysed by attenu-ated total reflectance spectroscopy (ATR-FTIR). Theincrease in surface concentration of carbonyl compoundswas used as a direct measure of the degree of ozonolysis[19].

Table 2 Interventions and their consequences on air exchange rates, recirculation/filtration rates, or surface area of sorptive materials

Location Control strategy Intervention Air exchange rate

(average)

(hour−1 )

Recirculation/

filtration rate

(hour−1 )

Added sorptive

surface

(m2 )

Room A Baseline (room ‘as is’) None 0.16 – –

Room A Passive sorption Semia textile (large room) 0.16 – 227

Room B Baseline (room ‘as is’) None 0.15 – –

Room B Passive sorption Semia textile (small room) 0.14 – 108

Room C Baseline (room ‘as is’) None 0.15 – –

Room C Reci rculation/fil tration Mobile stand-alone uni t.

Kemfilter unit, with HEPA particulate filter and a

combined charcoal and KMnO4 gaseous filter

0.15 2.5 –

Room D Baseline (room ‘as is’) None 0.13 – –

Room D Mechanical ventilation Constant operation, fixed flow.

Camfil CityCarb (EU7) particulate filter with

charcoal impregnation

0.96 – –

Room E Baseline (room ‘as is’) None (reference baseline) 0.12 – –

Room E Baseline (room ‘as is’) None (second reference baseline) 0.12 – –





Each type of dosimeter was exposed for the fullthree-month evaluation period. For all measurements(pollution, climate, dosimeters) the aim was to measure

at a point as close to the centre of the rooms as possiblewithout the sensors disturbing each other; typicallywithin the same cubic metre of space. Sensors weremostly placed on, or in front of, an empty shelf. Passivesamplers and the Purafil coupons were hung on Plexiglasracks, which freely exposed the samplers to the room air.Lead coupons were hung in a Plexiglas shelter designedin accordance with ISO 11844-2 [17]. This shelter gavesome protection from dust deposition, while it stillallowed a free airflow around the lead coupons. Dustdeposition tiles were placed horizontally on a shelfclose to its front edge. For short-term measurements,such as ultrafine particle or active VOC sampling,the instruments were installed near the centre of the

rooms mounted on a stand at a height of 1.5 m. Theoutdoor environment was monitored from a screenedweather station located on a nearby lawn. The designand installation followed the specifications of the WorldMeteorological Organization [20].

Estimate of uncertainty

The analysis of the impact of the different interventionsdepended on various factors, which differed in precision.For short-term analysis, such as the determination of air

exchange rate, or particle counting, the measurementhas a very high precision, to within a few per cent. Howwell the measurements represent long-term conditions

is difficult to estimate, given the imprecision thatweather and human activity will cause. On the otherhand, passive samplers and dosimeters accumulate thesample over a long time, and therefore reflect the averageconditions during the complete period of investigation.However, the precision of the various samplers differs;for example, the corrosion layer on silver coupons werereported with an accuracy of ±10Å, which in this studytypically gave uncertainties varying between <5 and20%. As another example, the organic acid sampling wascarried out in quadruplicate, and the result was reportedas the mean concentration plus or minus one standarddeviation. In order not to over-interpret the results ofthe different interventions, it is estimated that the criteria

for evaluation (change relative to reference room) shouldbe larger than ±25% before a change can be consideredsignificant.

RESULTS

The indoor concentrations and I/O ratios of the air-borne pollutants in all rooms are given in Table 3, bothfor baseline conditions and during the subsequentinterventions; the two reference baseline measurementsmade in Room E are also included. Especially for

Table 3 Airborne pollutants, their concentration and indoor-to-outdoor ratio (I/O)

Location and

intervention

Ozone Conc.

(ppb)

Ozone I/O

ratio

Nitrogen

dioxide Conc.

(ppb)

Nitrogen

dioxide I/O

ratio

Hydrogen

sulphide

Conc. (ppb)

Hydrogen

sulphide I/O

ratio

Organic acids

Conc. (ppb)

Ultrafine

particles

Conc. (cm−3 )

Ultrafine

particles I/O

ratio

Room A

Passive sorption

large room

(4.34)

4.69

(0.10)

0.18

(1.20)

3.76

(0.26)

0.54

(1.63)

1.67

(0.65)

0.80

(77.5)

70.5

(470)

700

(0.12)

0.07

Room B

Passive sorption

small room

(1.83)

1.44

(0.04)

0.06

(1.28)

2.03

(0.27)

0.29

(2.19)

1.81

(0.85)

0.86

(148)

124

(1800)

330

(0.45)

0.05

Room C

Recirculation/

filtration

(2.50)

2.26

(0.06)

0.09

(1.36)

2.57

(0.29)

0.37

(2.82)

2.13

(1.13)

1.02

(70.0)

181

(1000)

86

(0.20)

0.02

Room D

Mechanicalventilation constant

operation

(3.18)

2.53

(0.08)

0.10

(1.11)

4.16

(0.24)

0.60

(1.75)

2.30

(0.70)

1.10

(119)

152

(1900)

2400

(0.27)

0.21

Room E

Reference room

(first baseline)

second baseline

(1.82)

1.71

(0.04)

0.07

(1.26)

2.81

(0.27)

0.41

(3.13)

3.19

(1.24)

1.53

(151)

121

(640)

1500

(0.18)

0.12

Values in parentheses are initial baseline values measured in same room prior to intervention.





hydrogen sulphide, it may be noted that the I/O ratioswere generally around 1, or sometimes >1, whichimplies that hydrogen sulphide had indoor sources;

however, infiltration from outdoors also contributed tothe indoor level.In Figures 1 and 2 the relative effects of each of the

interventions are compared. The relative changes of theI/O ratios for outdoor pollutants and the concentrationsfor internally generated pollutants are compared in

Figure 1 The effect of interventions on pollutant levels in Rooms A–D. For pollutants that originate outdoors, the percentage change in the I/O ratio relative

to baseline is displayed. For pollutants that originate indoors, the percentage change in their concentration relative to baseline is displayed. The changes

are shown relative to the baseline variations, which were observed simultaneously in a reference room. Limonene plus pinene levels were only measured for

Room B.

Figure 2 The effect of interventions on dosimeter responses in Rooms A–D. The percentage change relative to the baseline for silver and lead corrosion

are shown, as well as dust deposition and the ozonolysis of latex rubber. The changes are shown relative to the baseline variations, which were observed

simultaneously in a reference room.

Figure 1. For the same locations and interventions,Figure 2 shows the change relative to baseline in dosi-meter responses. The diagrams are normalized to the

natural baseline variations that were simultaneouslyobserved in the reference location (Room E).The indoor temperature and relative humidity varied

between the rooms, but was largely within the normalroom temperature range and within a moderate rangeof relative humidity. Average temperature for all the

http://maney-prod.literatumonline.com/action/showImage?doi=10.1179/sic.2009.54.1.35&iName=master.img-001.jpg&w=281&h=174






locations varied between 19 and 23ºC, and the averagerelative humidity varied between 40 and 69%.

Passive sorption tests

The intervention in the small Room B produced morepronounced benefits than in the large Room A. Thisis consistent with the higher area-to-volume ratio ofthe Semia textile intervention in the smaller room,which increased the rate of sorptive removal (Figures1 and 2). The gaseous pollutant levels in the largeroom were approximately unchanged compared to thebaseline levels, although the nitrogen dioxide I/O ratioincreased slightly (37%). Room B was the only locationwhere VOCs were measured, and the concentrationof limonene plus pinene decreased significantly (89%)compared to the reference room. A similar decrease

(83%) was observed for ultrafine particles in the smallroom (Figure 1).

Mechanical ventilation tests

For Room D the ozone infiltration was effectivelydecreased whereas both nitrogen dioxide infiltration andthe concentration of organic acids showed unexpectedincreases (61–65%, see Figure 1). It was not anticipatedthat nitrogen dioxide would be removed to any greatextent by the charcoal in the combination filter.With regard to the organic acids, no decrease in theirconcentration was observed despite the increased venti-

lation rate in Room D. This suggests that the generationrate of the acids increased when the air exchangerate increased. Despite the moderate increase in theconcentration of organic acids and the slight increase inthe concentration of hydrogen sulphide in Room D, thecorrosion of silver and lead decreased (Figure 2).

Recirculation/filtration tests

Passing the room air through a stand-alone filtrationunit in Room C resulted in a decrease in the I/O ratiosor in the concentrations relative to baseline conditionsfor all pollutants except the organic acid concentration,

which displayed a relatively large increase (233%, seeFigure 1). The significant decrease of both ultrafineparticle concentration and dust deposition in RoomC (75–83% relative change, see Figures 1 and 2) wasexpected, given the high-efficiency particle filter in thestand-alone filtration unit. The dosimeter responses inRoom C displayed reduced corrosion, dust depositionand latex degradation. The reduced corrosion of the

lead dosimeter is worth noting, given the increase in theconcentration of organic acids. In general the use of astand-alone filtration unit proved effective in improving

the air quality.

DISCUSSION

Generally, it was expected that all the interventionswould improve the air quality and decrease the rateof material deterioration, due to either increasedsorptive removal or the dilution of indoor pollutantswith clean air; this was generally the case. For passivesorption, the intervention was more effective in thesmall Room B than in the larger Room A. The great-est improvements were observed in Room C withrecirculation and filtration through a stand-alone unit.Improved exchange of room air with outdoor air using

mechanical ventilation produced ambiguous results(Room D); any increase in ozone ingress was effectivelyavoided by charcoal filtration, but the concentration ofinternally generated organic acids increased despite theincreased ventilation rate (Room D).

Mitigation of ozone (outdoor pollutant)

The surface removal rates for ozone are shown inFigure 3 for each location during baseline conditions.The average removal rate was about 2.4 hour −1. Theremoval rates for all the rooms were, however, lower thanexpected given the high surface-to-volume ratios and

compared to values reported in other museum studies[2]. This may be due to the many ‘old’ or ‘aged’ objectsand interiors in the storage rooms. Other studies suggest

Figure 3 The surface removal rate for ozone measured at baseline

conditions (no interventions).






that oxidation processes due to ozone may decrease inrate over time as the reactive compounds are consumedfrom aging surfaces. This has, for example, been observed

for chamber experiments with ozone deposition oncarpets [21], ventilation filters [22], and a simulatedaircraft interior [23].

For the smaller rooms, passive sorption (RoomB) and recirculation through a stand-alone filter unit(Room C) had comparable effects on the removal ofozone, as both interventions caused a 14% decrease inthe I/O ratio compared to the reference room, while thepassive sorption in the larger Room A had no effect onozone. However, for both Rooms B and C the decreasein ozone ingress could not be considered significant. Incontrast, mechanical ventilation in Room D effectivelyremoved the ozone from the new air due to the charcoalpresent in the ventilation filter. Despite the increase in

air exchange (from 0.13 to 0.95 hour −1), the I/O ratioremained almost unchanged (0.08 to 0.10). The overallremoval rate, however, increased from 1.7 hour −1 for theroom alone, to 12 hour −1 for the room and the combinedEU7/charcoal filter. In other words, the filter removed alarge fraction of the incoming ozone (about 0.8 mg perhour) and, in contrast to the other interventions, thisozone was removed before it entered the room. Themechanical ventilation through the combined EU7/charcoal filter was the most effective intervention interms of ozone removal (Figure 1).

Dilution of internal pollutants

Some of the organic acid measurements from this studyare ambiguous compared to the model prediction.In Room D the concentration during mechanicalventilation was unexpectedly high (152 ppb), greaterthan the baseline measurement made before theventilation system was installed (119 ppb). In addition,the concentration in Room C with the recirculation/filtration unit was much higher than expected (181 ppb),as the level more than doubled when the recirculation/filtration unit was installed. This implies that the genera-tion rate was not constant inside these rooms, but thatit increased, although it is not clear why the emission

of organic acids would increase. According to the massbalance in equation 1, the concentration should havedecreased, assuming the generation and sorption rateswere constant. Temporal variations in organic acidemission rates for changing ventilation rates have beenobserved elsewhere, for example, in new houses [24].An additional source of organic acids could be theventilation filters, which may release secondary organic

pollutants due to oxidation processes between ozone andother organic compounds on the surface of the filtermedia [22, 25]. However, these explanations all contrast

with the decreased rate of lead corrosion relative to thereference room, a point that will be addressed below.

Control of particles and dust

The mechanical filtration was effective in reducing part-iculates. This was to be expected, especially for Room C(recirculation/filtration), as the filter unit was equippedwith a high-efficiency particle-arresting filter. In thiscase both fine and coarse particle levels showed 75–83%less change than the reference room.

Of note was the observation made in the small RoomB, with sorptive walls, in which the I/O ratio of ultrafineparticles decreased from 0.45 before the installation of

the wall covering to just 0.05 while the wall coveringwas in use. During the same two periods the referenceroom only experienced a change in I/O ratio from 0.18to 0.12. This substantial decrease in particle I/O ratiomay reflect that less generation of ultrafine particlestook place indoors. It has been shown that indoorreactions between ozone and organic compounds canbe a significant source of ultrafine particles [26], andsome short-term measurements indicated that thesorptive wall coverings removed a considerable fractionof the volatile organic compounds from the air. On twooccasions, with and without the sorptive wall coveringsinstalled, a VOC screening was performed both in the

room with wall coverings and in the reference room.While the pinene plus limonene concentrations werealmost identical in the two rooms when no sorptive wallcoverings were present (39 and 41 µg·m−3), there was asignificant difference after the sorptive wall coverings hadbeen installed for ten weeks: 5 µg·m−3 in the room withsorptive walls compared to 46 µg·m−3 in the referenceroom. The sorptive wall coverings caused an 89% relativedecrease in pinene plus limonene concentration withrespect to the reference room.

Observed material damage rates

All the rooms showed significantly less silver and leadcorrosion relative to the reference room (Figure 2).However, in Room D, with mechanical ventilation,the silver corrosion decrease was less pronounced thanfor the remainder of the rooms (39% less change ascompared to 70–79% less change relative to referenceroom). This corresponds to the observations forhydrogen sulphide for the same room, the concentration





of which increased despite the intervention (29% morechange relative to reference room, Figure 1).

For all the rooms the lead corrosion likewise

significantly decreased relative to the reference room(Figure 2). At first, this seems contrary to the observationof large increases in organic acid concentrations duringthe recirculation and mechanical ventilation tests (Figure1). However, one explanation for this is an observationmade during the preparation and calibration of the leaddosimeters, when it was found from multi-regressionanalysis that when both hydrogen sulphide and organicacids were present at the same time the corrosion ratewas proportional to the concentration of organic acids,but inversely proportional to the concentration ofhydrogen sulphide [18]. This could be due to the lightpassivation layer formed by hydrogen sulphide, whichthen retards organic acid from forming a much heavier

corrosion product.The degree of ozonolysis of latex samples did not vary

much during any of the interventions (Figure 2). Thelatex dosimeter responds to ozone dosage (concentrationdependent) rather than the I/O ratio, so the variationsin response reflect the absolute concentration variationsbetween the rooms.

Impact of low air exchange rate

The natural air exchange rate for all the rooms was lessthan 0.2 hour −1, and even during mechanical ventilation

the exchange rate was kept below 1 hour −1. It can beseen from Figure 4 that for a hypothetical room theconcentration of pollutants generated indoors – such

as organic acids – depends on the air exchange rate,assuming that the outdoor concentration is negligibleand that the indoor generation rate is constant. Threescenarios are shown: a model of a highly sorptive roomwith a surface removal rate of 2.5 hour −1, a normal roomwith a surface removal rate of 0.25 hour −1 and an inertroom with no surface removal at all. For comparisonthe organic acid data from this study are plotted on thediagram, although it is acknowledged that the real datapoints represent different rooms with varying conditions.According to the prediction, both an increase in airexchange or in the surface removal rate will decreasethe pollution concentration, but below air exchangerates of about 2 hour −1 the surface removal rate will

start to become the dominant factor, while at higher airexchange rates it is this factor that controls the pollutionconcentration.

In general, it is quite efficient to shield out ambientpollutants by having a low air exchange rate. This isillustrated in Figure 5, which shows the indoor concen-tration dependency for ozone on the air exchange ratemodelled in three situations: a room with a high ozonesurface removal constant of 10 hour −1, a room with amoderate removal constant of 1 hour −1, and a roomwith low sorptivity and a removal rate of just 0.1 hour −1.All ozone data from this field study are plotted on the

Figure 4 The concentration of indoor-generated pollutants (organic acids) in a hypothetical room of 150 m3 versus the air exchange rate. The steady state

concentrations were modelled from Equation 1 at three different removal rates (S). The examples assume negligible outdoor concentration and a constant

indoor generation rate of 50 mg per hour, which would be a realistic scenario for an environment containing a large amount of wooden furniture or objects.

For the sake of comparison the points illustrate real measurements from the different storage rooms included in this study.






diagram for comparison, again acknowledging thatthere are indeed variations in conditions between theindividual locations. The rooms modelled and the datapoints in Figures 4 and 5 underline that the most efficientway to avoid high pollution levels is a combination of alow air exchange rate and a high surface removal rate.This is also evident from the observations in this study,where the room with internal recirculation/filtrationgenerally performed best. It should be noted that the

energy use of a mobile unit may be higher than for anintegrated building air-handling system, which has theadvantage of using larger, more energy-efficient fans.

For the passive sorption experiments another factorshould be taken into account. For both rooms it was inpractice difficult to fit much extra surface area into analready highly loaded room, while maintaining its mainfunction. Much of the surface area was not added, butmerely replaced other surfaces; for example, the newtextile covered the existing wall materials. It should alsobe noted that these experiments were carried out withnew materials and that their long-term sorption capacityis not known.

CONCLUSIONS

Initially all the storage rooms were ventilated at a lowexchange rate. Mechanical ventilation and recirculation/filtration was achieved by the use of a mobile stand-alone unit or a new ventilation system installed forthis study. Ventilation rates were kept low (even when

increased they were never above 1 hour −1), while therecirculation rate was around 2.5 hour −1. Passive sorptionwas initiated by hanging sheets of sorptive textile on thewalls and other free surfaces.

Passive sorption using highly sorptive wall coveringsperformed better in a small room compared to a largeroom, since it was possible to install a greater surface-to-volume ratio of sorptive material. However, it wasdifficult to fit in much extra surface while maintaining

the room’s main function and the increased pollutantremoval may therefore not be as significant as expected.

Of all the interventions, mechanical ventilationcoupled with charcoal filtration gave the best mitigationof ozone. However, at the same time it resulted in anincrease in nitrogen dioxide concentration. Increasedmechanical ventilation should dilute internally generatedpollutants, but ambiguous results from this study implythat the emission rates for internally generated pollutantssuch as organic acids may also vary, so it is difficult topredict the benefits from increased ventilation. Thegeneration of organic pollutants may even take place onthe filter itself, via reactions involving ozone.

Recirculation of room air through a stand-alonefiltration unit was the most successful intervention inthis study. This may be due to the possibility of achievinga higher recirculation/filtration rate than can be achievedusing mechanical ventilation, while avoiding an adverseimpact on the climate in the room. Like mechanicalventilation, recirculation/filtration also producedambiguous results as the concentration of organic acids

Figure 5 The concentration of ozone in three hypothetical rooms versus the air exchange rate. The steady state concentrations were modelled from

Equation 1, assuming no indoor sources, an outdoor concentration of 30 ppb, and for three different surface removal rates (S). For the sake of comparisonthe points illustrate real measurements from the different storage rooms included in this study.






increased despite the increased recirculation/filtrationrate. The HEPA grade particle filter in the recirculationunit was very effective in reducing the concentration of

ultrafine particles.When the ventilation rate is very low, surface reac-tions are the main loss mechanism for air pollutants.Keeping in mind that surface deposition on objects fromthe collection is part of the deterioration route for theseobjects, it is important to expose as much ‘sacrificial’surface material as possible (e.g. on walls) compared tothe surface area of the collection itself, or to introduceother pollution sinks (e.g. filters). Passive surface removalusing sorptive wall coverings can provide an overallremoval rate equal to the removal rate provided by theair exchange. However, aided by mechanical filtrationunits the overall removal rate can be increased by a factorof 10. The ozone surface removal rates observed in this

study were generally low, ranging from 1.8 to 3.2 hour −1 under baseline conditions. The generally low removalrates could reflect the presence of ‘aged’ surface mater ialsthat are less susceptible toward ozone deposition.

Taking the uncertainties of the various factors intoaccount, a cautious conclusion is that a combination ofa low air exchange rate and internal recirculation withadequate filtration will be most beneficial to indoor airquality for the type of low-activity rooms which weresurveyed in this study. However, it must be stressed thatother buildings and the ambient conditions may differ,so that other factors will influence the indoor air quality.A crucial factor is the quality of filtration systems, with

regard to unwanted chemical side-effects such as theproduction of secondary organic acids on the filtermedia. In existing facilities mobile stand-alone filtrationunits can readily be used, whereas recirculation/filtrationunits may be integrated into the building’s air-handlingsystem when building new facilities.

ACKNOWLEDGEMENTS

The authors sincerely thank Charles J. Weschler, Inter-national Centre for Indoor Environment and Energy atthe Technical University of Denmark, for valuable discus-sions throughout the study. Thanks are due to Tunga

Salthammer and Alexandra Schieweck of the FraunhoferWilhelm-Klauditz-Institut, Germany, who conductedthe VOC analysis, and Maria-Louise Jacobsen fromThe National Museum of Denmark, who performedthe dust analysis. The help and support received fromthe management and staff at the storage facilities of theNational Museum of Denmark is highly appreciated.

This work was part of a PhD project by one ofthe authors (M. R.-S.) financed by the School ofConservation at the Royal Danish Academy of Fine Arts,

and carried out in cooperation with the InternationalCentre of Indoor Environment and Energy at theTechnical University of Denmark. Support has gratefullybeen received from Beckett Fonden, Denmark (financialsupport for air pollution sampling), and Kemfilter AB,Söderhamn, Sweden (loan of equipment).

MATERIALS AND SUPPLIERS

BVDA environmental gel lifters, No. B-17000: P-B Miljø,Enebærvej 7, DK-8850 Bjerringbro, Denmark.

CityCarb filter: Camfil Farr, Gladsaxevej 342, DK-2860 Søborg,Denmark.

Image J software (Image Processing and Analysis in Java): http://rsb.info.nih.gov/ij/ (accessed 12 January 2009).

IPI preservation environment monitors: Image PermanenceInstitute, Rochester Institute of Technology, Building 7B, room2000, 70 Lomb Memorial Drive, Rochester, NY 14623-5604,USA.

Maximus 700 mobile filter unit: Kemfilter AB, Björnängsvägen 2,S-82640 Söderhamn, Sweden.

Multigas monitor 1302: Innova Air Tech Instruments, Energivej 30,DK-2750 Ballerup, Denmark.

P-Trak ultrafine particle counter 8525: TSI Inc., 500 Cardigan

Road, Shoreview, MN 55126, USA.

Purafil environmental reactivity coupons (ERC): Purafil Inc., 2654Weaver Way, Doraville, GA 30340, USA.

Semia: Asahi Kasei Fibers Corporation, Shin-Dai Building, 2-6Dojimahama 1-chome Kita-ku, Osaka 530-8205, Japan.

Tiny Tag data loggers: Gemini Data Loggers Ltd., Scientific House,Terminus Road, Chichester, West Sussex, PO19 8UJ, UK.

REFERENCES

1 Padfield, T., and Larsen, P.K., ‘How to design museums witha naturally stable climate’, Studies in Conservation 49 (2004)131–137.

2 Ryhl-Svendsen, M., ‘Indoor air pollution in museums: Predictionmodels and control strategies’, Reviews in Conservation 7 (2006)27–41.

3 Hollinger, W.K., ‘Microchamber papers used as a preventiveconservation material’, in Preventive Conservation: Practice, Theory

and Research, ed. A. Roy and P. Smith, International Institute forConservation, London (1994) 212–216.





4 Sakr, W., Weschler, C.J., and Fanger, P.O., ‘The impact ofsorption on perceived indoor air quality’, Indoor Air 16 (2006)98–110.

5 Baer, N.S., and Banks, P.N., ‘Indoor air pollution: Effects on

cultural and historic materials’, The International Journal ofMuseum Management and Curatorship 4 (1985) 9–20.

6 Graedel, T.E., and McGill, R., ‘Degradation of materials in theatmosphere’, Environmental Science and Technology 20 (1986)1093–1100.

7 Brimblecombe, P., ‘The composition of museum atmospheres’, Atmospheric Environment 24B (1990) 1–8.

8 Blades, N., Oreszczyn, T., Bordass, B., and Cassar, M., Guidelines

on Pollution Control in Museum Buildings, Museums Association,London (2000).

9 Hatchfield, P., Pollutants in the Museum Environment: Practical

Strategies for Problem Solving in Design, Exhibition and Storage, Archetype, London (2002).

10 Tétreault, J., Airborne Pollutants in Museums, Galleries and Archives:

Risk Assessment, Control Strategies and Preservation Management ,Canadian Conservation Institute, Ottawa (2003).

11 De Santoli, L., Muller, C., Prina, A., and Sacchi, E., ‘Controlstrategies for gaseous contamination in museums: A newmethod for assessing environmental risk’, in Tecnologie

Impiantistiche per i Musei, Roma, 6 maggio 2005 , ed. L. DeSantoli, Associazione Italiana Condizionamento dell’AriaRiscaldamento e Refrigerazione (AICARR), Milan (2005)321–333.

12 Muller, C., ‘Practical applications of reactivity monitoring inmuseums and archives’, in Conservation Science 2002, Edinburgh,

22–24 May 2002, ed. J.H. Townsend, K. Eremin and A. Adrians,Archetype, London (2002) 50–57.

13 De Santis, F., Vazzana, C., Menichelli, S., and Allegr ini, I., ‘Themeasurement of atmospheric pollutants by passive sampling

at the Uffizi Gallery, Florence’, Annali di Chemica 93 (2003)45–53.

14 De Santis, F., Allegrini, I., Bellagotti, R., Vichi, F., and Zona,D., ‘Development and field evaluation of a new diffusivesampler for hydrogen sulfide in the ambient air’, Analytical and

Bioanalytical Chemistry 384 (2006) 897–901.15 Watts, S.F., Ridge, L., Rendell, A.R., Grebenik, P.D., Miller, A.,

and Reid, A.J., ‘The use of diffusion tubes (Palme’s tubes) forassessing air quality in indoor and outdoor environments’, inProceedings of the 4th International Conference on Urban Air Quality:

Measuring, Modelling and Management , ed. R.S. Sokhi and J.Brechler, Institute of Physics, Prague (2003).

16 Grieve, P., Measuring Ventilation Using Tracer-Gases, Brüel & Kjær,Nærum Denmark (1991).

17 ISO 11844–2, Corrosion of Metals and Alloys. Classification of

Low Corrosivity of Indoor Atmospheres – Part 2: Determination of

Corrosion Attack in Indoor Atmospheres, International Organizationfor Standardization, Geneva (2005).

18 Ryhl-Svendsen, M., ‘Corrosivity measurements of indoormuseum environments using lead coupons as dosimeters’, Journal of Cultural Heritage 9 (2008) 285–293.

19 Ryhl-Svendsen, M., ‘Ozone detection using natural rubberdosimeters: Quantitative measurements using light microscopy

and attenuated total reflectance spectroscopy’, Zeitschrift fur

Kunsttechnologie und Konservierung 21(2) (2007) 240–249.20 WMO, Guide to Meteorological Instruments and Methods of

Observation, 6th edn, Publication No. 8, World Meteorological

Organization, Geneva (1996).21 Morr ison, G.C., and Nazaroff, W.W., ‘Ozone interactions with

carpets: Secondary emissions of aldehydes’, Environmental Science

and Technology 36 (2002) 2185–2192.22 Bekö, G., Halás, O., Clausen, G., and Weschler, C.J., ‘Initial

studies of oxidative processes on filter surfaces and their impacton perceived air quality’, Indoor Air 16 (2006) 56–64.

23 Tamás, G., Weschler, C.J., Bakó-Biró, Z., Wyon, D.P., andStrøm-Tejsen, P., ‘Factors affecting ozone removal rates in asimulated aircraft cabin environment’, Atmospheric Environment 40 (2006) 6122–6133.

24 Hodgson, A.T., Rudd, A.F., Beal, D., and Chandra, S., ‘Volatileorganic compound concentrations and emission rates in newmanufactured and site-built houses’, Indoor Air 10 (2000)178–192.

25 Bekö, G., Clausen, G., and Weschler, C.J., ‘Further studies ofoxidation processes on filter surfaces: Evidence for oxidationproducts and the influence of time in service’, Atmospher ic

Environment 41 (2007) 5202–5212.26 Weschler, C.J., and Shields, H.C., ‘Indoor ozone/terpene

reactions as a source of indoor particles’, Atmospheric Environment

33 (1999) 2301–2312.

AUTHORS

MORTEN R YHL-SVENDSEN received a Master’s degree inconservation from the School of Conservation at theRoyal Danish Academy of Fine Arts, Denmark, in 2001.

He has worked as a conservator at the Danish Museumfor Photographic Art, and at the National Museum ofDenmark, mainly in preventive conservation. In 2007he finished a PhD at the School of Conservation on airquality in museum storage buildings, in cooperation withthe International Centre of Indoor Environment andEnergy at the Technical University of Denmark. Address:National Museum of Denmark, Department of Conservation,I.C. Modewegs Vej, DK-2800 Kgs. Lyngby, Denmark. Email:[email protected]

GEO CLAUSEN is associate professor and scientific co-ordinator at the International Centre for Indoor Environ-

ment and Energy, Technical University of Denmark. Hereceived his PhD in mechanical engineering from thesame university in 1986. His research activities, whichfocus on the indoor environment and its impact on man,have been documented in more than 75 publicationsin refereed journals and conference proceedings. Ofparticular interest here are his comparative studies forthe relative impact on man of the thermal environment,





indoor air pollution and noise. Address: Technical Universityof Denmark, Department of Civil Engineering, Building 402,

Nils Koppels Allé, DK-2800 Kgs. Lyngby, Denmark. Email: [email protected]

Résumé — Les effets de la ventilation mécanique, de la filtration et de l’absorption passive sur la qualité de l’air intérieuront été étudiés dans cinq réserves du Musée national du Danemark. La ventilation mécanique et la recirculation/filtration del’air ont été mises en œuvre en installant de nouvelles unités de ventilation et de filtration. L’absorption passive a été mise enœuvre en suspendant des feuilles de matériaux absorbants sur les murs. Les stratégies de contrôle ont été évaluées en fonction deleur capacité à abaisser la concentration des polluants générés à l’intérieur ainsi que le rapport des concentrations de polluantsextérieurs mesurées à l’intérieur et à l’extérieur. L’impact global de chaque méthode sur l’environnement a été évalué au moyende dosimètres. On a trouvé que l’absorption passive se révélait bien meilleure dans les petites pièces que dans les grandes. Laventilation mécanique et la filtration au charbon actif ont fourni une bonne protection contre l’ozone, mais se sont révélées moinsefficaces en ce qui concerne la réduction du dioxyde d’azote. On pouvait s’attendre à ce que l’augmentation du taux de ventilationdilue les polluants générés à l’intérieur, mais des résultats ambigus ont montré que le taux d’émission des acides organiques

pouvait être également très variable. La recirculation/filtration semble être la méthode la plus efficace. Une conclusion prudente

est que la combinaison d’un faible taux de renouvellement de l’air combiné à la recirculation/filtration serait la solution la plusbénéfique pour améliorer la qualité de l’air ambiant dans de telles réserves où il y a peu d’activité.

Zusammenfassung — In fünf Depoträumen des Dänischen Nationalmuseums wurde der Effekt mechanischer Belüftung,Filtration und passiver Sorption auf die Qualität der Innenluft untersucht. Durch Einführung neuer Ventilations- undFiltrationseinheiten wurden die Ventilation und die Filtration gestartet. Durch Aufhängen von Platten aus Sorptionsmaterialwurde eine passive Sorption erreicht. Die Kontrollstrategien wurden hinsichtlich ihrer Fähigkeit begutachtet, intern erzeugteSchadstoffe sowie das Verhältnis der Schadstoffe im Innen- und Außenraum zu minimieren. Der Gesamteinfluss wurde für jedeMethode anhand von Dosimetern bestimmt. Es konnte gezeigt werden, dass passive Sorptionsmaterialien in kleinen RäumenEffektiver sind als in großen. Mechanische Belüftung und Filterung durch Aktivkohle konnten sehr gut gegen Ozon schützen,waren aber weniger effektiv bei der Reduktion von Stickoxiden. von einer gesteigerten Ventialtion wurde eine weitere Reduktionder im Innenraum generierten Schadstoffe erwartet, indessen legen die nicht eindeutigen Ergebnisse den Schluß nahe, dass auchdie Menge der entstehenden organischen Säuren schwanken kann. Luftumwälzung mit Filtration war die effektivste Methode.

Dies lässt den vorsichtigen Schluß zu, dass eine Kombination einer kleinen Luftaustauschrate mit interner Luftumwälzung mitFiltration sich auf die Qualität der Innenluft am besten auswirkt.

Resumen — Se desar rolló una investigación en relación a cinco salas de almacenaje del National Museum de Dinamarca,en la que se estudió la calidad del aire interior por el efecto de la ventilación mecánica, la filtración y la absorción pasiva. Laventilación mecánica y la recirculación/filtración fueron iniciadas al introducir nuevas unidades de aireación y filtración. Laabsorción pasiva se inició mediante la colocación de paneles de materiales absorbentes en la paredes. Las estrategias de control

fueron evaluadas en términos de su capacidad para reducir la cantidad de contaminantes generados en el interior, así como enlos niveles de contaminantes externos por el intercambio interior-exterior. Se evaluó el impacto ambiental genérico para cadamétodo mediante el uso de dosímetros. Se observó, así mismo, que la absorción pasiva mejoraba más en las salas pequeñas queen las grandes. La ventilación mecánica y la filtración con carbón activado proporcionaron una alta protección contra el ozono, peroeran menos efectivas para reducir el dióxido de nitrógeno. Con el aumento de los niveles de ventilación se esperaba mejorar ladisolución los contaminantes generados internamente, pero los resultados ambiguos que se obtuvieron implicaban que la emisión

de ácidos orgánicos también podía variar. El método más eficiente fue, generalmente, la recirculación/filtración del aire. Unaconclusión prudente a todo ello puede resumirse como que el sistema más beneficioso para la calidad del aire interior, en zonas dealmacenamiento con baja actividad humana, es la combinación de un bajo intercambio de aire con el exterior y una recirculacióninterna con filtración.

the effect of ventilation, filtration and

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