diurnal pattern of submicron aerosol size/mass distributions in urban atmosphere, prague winter...

DIURNAL PATTERN OF SUBMICRON AEROSOL SIZE/MASS DISTRIBUTIONS IN URBAN ATMOSPHERE,

PRAGUE WINTER 2004/2005

J. HOVORKA1, M .BRANIŠ1, J. SCHWARZ2

hovorka@cesnet.cz, branis@natur.cuni.cz, schwarz@icpf.cas.cz

1 Institute for Environmental Studies, Faculty of Science, Charles University in Prague, Benátská 2, 128 01 Prague 2, Czech Republic

2 Institute of Chemical Process Fundamentals AS CR, Rozvojová 135, 165 02 Prague 6, Czech Republic 

The study was conducted within the project „Comprehensive size resolved characterization of atmospheric particulate matter in Prague“ supported by GACR grant No. 205/03/1560

Roof-top (25 m above street level) sampling on building situated on the University Botanic garden (3.5 ha) in Prague centre, NO street canyon conditions

Parameters measured at the station: 5 min. integrates of aerosol size distributions 14 – 710 nm (SMPS-3936L25, TSI)

15 min. integrates of gaseous components concentrations NOx, volatile hydrocarbons CH4 and non-methane – NMHC, CO, O3, SO2 by automatic analysers (Horiba-360 series)

15 min. integrates of wind speed, wind direction, temperature, relative humidity, UV-A,B

24/1/2005, Monday

24/12/2004, Friday12/12/2004, Sunday

24/1/2004, Monday 22/12/2004, Wednesday

Lower values of number and mass concentrations of aerosol particles suspended in the urban air were clearly associated with higher wind speed values regardless the type of day

During cal/moderate wind speed conditions diurnal pattern of aerosol size distribution vary significantly from day to day. The diurnal pattern is characteristic result of multi-phase system influence. Every day has to be treated separately to reveal possible causes of the diurnal patter

Typically, the total aerosol number was dominated by the influence of mobile sources (GMD about 50 nm), while the total aerosol mass is predominantly influenced by stationary (natural gas burning) sources (GMD 80-100 nm)

Working days usually exhibit morning ( 8-10 a.m.) peaks associated with traffic rush hours

Majority of days exhibit late evening, round midnight and very early morning maximas in number size ditributions associated with higher natural gas burn-up in the stationary heating sources nearby

Not a one true nucleation event (“banana” shape graph) was recorded during the measured period

Conclusions

Weekends/holidays

• Sunday 12/12/2004:

By low temperatures induced higher natural

gas burn-up (indicated by CH4, further in the

text abbreviated as “by …”) and calm air

condition resulted in midnight maximum.

Contrary to this maximum, near midday peak

is caused by sources of in-complete

combustion (by CO). This should be

combination of again natural gas burn-up( by

GMD 90 and by CH4, NO2) and mobile

sources (by NO, NMHC) also characterized

by an immediate increase in particle numbers

and maximas in aerosol number distribution

near 50 nm sizes.

• Friday 24/12/2004, Christmas day

Low level of transportation and mainly high

wind speed resulted in exceptionally low

aerosol number and mass. Near-to-midnight

peak is caused by gradually increasing

natural gas burn-up starting from 4 p.m. (by

CH4) when people stay home. Higher

temperature also induced lower natural gas

consumption

Working days

• Monday 24/1/2005:

Low number concentrations are gradually

increasing from 4 a.m. due to gas burn-up

(by CH4) culminating near 9 and 10:30 a.m.

and 3 p.m. in coincidence with transportation

(NO, NMHC). It is difficult to distinguish

influence of mobile from stationary ones on

aerosol number and mass. Sudden peaks in

total aerosol mass at 8 a.m and 4 and 6 p.m.

may indicate the higher activity of stationary

sources.

• Wednesday 22/12/2004:

Low temperature during night-time induced

high natural gas burn-up (by CH4, CO, NO2)

producing aerosol with GMD 90-100 nm

sizes. Then the maximas are formed with

GMD 50 nm at 8,9 and 10 a.m. typically

caused by transportation (by NO, NMHC).

Though the concentrations of NO2 remains

high, gradual increase in temperature and

wind speed causes gradual decrease in total

aerosol number and mass . Smog episode

day.