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