Why do we Measure

Precipitation Chemistry?

Christopher Lehmann

CAL Director

2007 Field Operations Training Course

Atmospheric Deposition

EMISSIONS

REMOVAL

Precipitation volume/time

AQUEOUS PHASEPRECIPITATION

GAS/PARTICULATE PHASEAEROSOL PARTICLES

& GASES

Deposition velocity

ATMOSPHERIC TRANSPORT & TRANSFORMATION

REACTIONS

ENVIRONMENTALIMPACTS

Environmental Impacts

• Stream and lake acidification

• Increased fish mortality (eggs, fry)

U.S. EPA, 2002: Response of Surface Water Chemistry to the Clean Air Act Amendments of 1990.

pH effects on fish population

Source: HBRF, Acid Rain Revisited, 2001

OH494.3

MO035.0

Environmental Impacts

• Stream and lake acidification

• Increased fish mortality (eggs, fry)

• Damage to vegetation

Damage to forests

Mt. Mitchell, North Carolina

Acid deposition effects

Source: HBRF, Acid Rain Revisited, 2001

Environmental Impacts

• Stream and lake acidification

• Increased fish mortality (eggs, fry)

• Damage to vegetation

• Benefits certain agricultural crops (reduces fertilizer needed)

• Benefits invasive species

Environmental Impacts

• Contributes to wetland nutrient loads

Nitrogen damage to

aquatic systems

Nitrogen Effects

Environmental Impacts

• Contributes to wetland nutrient loads

• Bioaccumulates in aquatic environments (Hg)

The mercury problem?Bioaccumulation

Bacterial action(water and sediment)

Zooplankton

Smaller fish predatory fish

Water Body

Me-Mercury

Concentration

Dry Deposition

Wet DepositionGeologic Sources(soil, rock, base flow etc.)

Methylation

Hg Hg Hg

Environmental Impacts

• Contributes to wetland nutrient loads

• Bioaccumulates in aquatic environments (Hg)

• Damage to buildings, structures, and statues

• Corrosion of materials

Limestone statue of George Washington first put outside in New York City in 1944

Source: ACS, Chemistry in Context, 2006

The NADP

• 3 Precipitation monitoring networks– National Trends Network (NTN) – Atmospheric Integrated Research Monitoring

Network (AIRMoN)– Mercury Deposition Network (MDN)

• 2 Analytical Laboratories– Central Analytical Laboratory, ISWS– Frontier Geosciences, Seattle, WA

acidic speciesfree acidity (or pH), sulfate, nitrate, chloride

nutrientsnitrate, ammonium, orthophosphate

earth crustal base cations calcium, magnesium, potassium

saltssodium and chloride

heavy metalsmercury, trace metals (MDN)

Species Measured by the NADP

Precipitation Acidity: pH

pH is the power of hydrogen, a measurement of the hydrogen ion concentration

pH = -log10([H+], mol/L)

H2Ol H+aq

+ OH-aq

pH 7 is NEUTRAL: [H+] = [OH-]

acid base

Acidic PrecipitationAcidic precipitation or acid rain is defined at pH

< 5.0 to relfect human-induced pollution

Why…..

• Carbon dioxide in air– CO2,g + H2Ol = H2CO3,aq (carbonic acid)

– PCO2 = 350 ppm pH ~ 5.6

• Naturally occurring acid species also reduce the pH of rain

– sulfate from oceans– organic acids

Is “Acid Rain” still an issue?

Sulfate (SO42-) &

Nitrate (NO3-)

1. Sulfur dioxide conversion to sulfite:

2. Oxidation of sulfite to sulfate:

Atmospheric Reactions: Conversion of Sulfur Dioxide to Sulfate

SO2 + H2O ↔ SO2∙ H2OSO2∙ H2O ↔ H+ + HSO3

-

HSO3- ↔ H+ + SO3

2-

One pathway by ozone: SO32- + O3 ↔ SO4

2- + O2

can also be oxidized by hydrogen peroxide, OH radicals, nitrogen oxides, formaldehyde, iron, and manganese

Seinfeld and Pandis, 1998

SO2,g

SO42-aq

CONCENTRATION = Mass of pollutants per unit volume of water collected

1.91 mg/L sulfate ionBondville, IL in 2005 (average)

DEPOSITION = Mass ofpollutant that falls on a fixed unit of area

17.2 kg/ha sulfate ion Bondville, IL in 2005 (total)

100 m

1 ha = 104 m2

1.91 milligrams of sulfate dissolved in 1 liter of water

17.2 kilograms of sulfate spread over 1 hectare in one year

Atmospheric Reactions: Conversion of Nitrogen Dioxide to Nitrate

NO2 + OH∙ + M ↔ HNO3 + MHNO3 + H2O ↔ H+ + NO3

-

Seinfeld and Pandis, 1998

HNO3,g

NO3-aq

NO2,g HNO3,g

Ammonium (NH4+)

Atmospheric Reactions: Conversion of Ammonia to Ammonium

NH3 + H2O ↔ NH3∙H2ONH3∙H2O ↔ NH4

+ + OH-

Seinfeld and Pandis, 1998

NH3,g

NH4+aq

Crustal Cations:Calcium (Ca2+), Magnesium (Mg2+) & Potassium (K+)

What is the role of base cations in precipitation chemistry?

Base cations neutralize the affects of acidic precipitation

anion sum(1) cation sum(2) pH MN = 74 88 6.31

NY = 74 22 4.34

(1) anions = sulfate, nitrate, and chloride

(2) cations = ammonium, calcium, magnesium, potassium, and sodium

Base Cations & Sample Collection

Important sampling considerations:Please ensure that sample is WET ONLY! Watch the event recorder tracing on the raingageEnsure that the NTN sampler is operating properlyNote unusual events at site (burning, farm activities,

construction, etc.) and record this information in the comments section of the FORF

Large dust particles dry deposit efficiently NY could look like MN due to base cation increases

Why Shouldn’t I use Tap Water? NADP/NTN Site in Ohio (microequivalents/liter)

Cl- = 7

SO4 2- = 69

NO3- = 32

anion sum = 108 (sulfate, nitrate, and chloride)

cation sum = 33 (ammonium, calcium, magnesium, potassium, sodium)

Champaign Urbana Water (microequivalents/liter)

Cl- = 234

SO4 2- = 650

NO3- = 3

anion sum = 887cation sum = 3062

Please use only deionized water andlaboratory wipes to clean the NADPcollector.

Do not re-wash, rise, or otherwise cleanthe supplies provided by the CALunless you are instructed to do so.

Questions?

Please remember to fill out your critique

as you complete each section