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Section 7 Chemical Aspects of Air Pollution

Overview of Basic Pollutants Ozone Particulate Matter Carbon Monoxide Sulfur Dioxide Nitrogen Oxides

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Section 7 – Chemical Aspects of Air Pollution 2

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Photochemical Smog

Air pollution formed by sunlight catalyzing chemical reactions of emitted compounds

Los Angeles, California • Early pollution due to London-type smog.

1905-1912, L.A. City Council adopts regulation controlling smoke • Early 1900’s, automobile use increases.

1939-1943 visibility decreases significantly.

• Plume of pollution engulfs downtown (26 July 1943).

1943: L.A. County Board of Supervisors bans emission of dense smoke and creates office called Director of Air Pollution Control • 1945. L.A. Health Officer suggests pollution due to locomotives, diesel trucks, backyard incinerators, lumber mills, dumps, cars.

• 1946. L.A. Times hires air pollution expert to find methods to ameliorate pollution.

Section 7 – Chemical Aspects of Air Pollution 3

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Los Angeles, California (December 3, 1909)

Library of Congress Prints and Photographs Division, Washington, D. C.

Section 7 – Chemical Aspects of Air Pollution 4

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Discovery of Ozone in Smog

• 1948: Arie Haagen-Smit (1900-1977), biochemistry professor at Caltech, begins to study plants damaged by smog.

• 1950: Finds that plants sealed in a chamber and exposed to ozone exhibit similar damage as did plants in smog • Also finds that ozone caused eye irritation, damage to materials, respiratory problems.

• Other researchers find that rubber cracks within minutes when exposed to high ozone.

• 1952: Haagen-Smit finds that ozone forms when oxides of nitrogen and reactive organic gases are exposed to sunlight. Postulates that ozone and precursors are main constituents of L.A. smog.

• Oil companies and business leaders argue that ozone in L.A. originates from stratosphere.

• Measurements of low ozone over Catalina Island disprove this.

Section 7 – Chemical Aspects of Air Pollution 5

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Basic Pollutants

(1 of 3)

Categories of pollutants

● ● Primary – emitted directly from a source Secondary – formed in the atmosphere from a reaction of primary pollutants ● Precursors – primary pollutants (gases) that participate in the formation of secondary pollutants

Pollutants originate from

● ● ● Combustion of fossil fuels and organic matter Evaporation of petroleum products or compounds used in commercial products, services, and manufacturing Natural production of smoke from fires, dust from strong winds, and emissions from the biosphere and geosphere Section 7 – Chemical Aspects of Air Pollution 6

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Basic Pollutants

(2 of 3) Pollutant Abbreviation Type Carbon Monoxide CO Primary Sulfur Dioxide Ozone SO 2 O 3 Primary Secondary Nitrogen Dioxide Hydrocarbon Compounds (also called VOCs – volatile organic compounds ) NO HC 2 Secondary Primary & Secondary Particulate Matter PM Section 7 – Chemical Aspects of Air Pollution Primary & Secondary 7

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Basic Pollutants

(3 of 3) Section 7 – Chemical Aspects of Air Pollution 8

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Basic Pollutants – Toxics

(1 of 2) ● ● Air toxics (hazardous air pollutants) are known or suspected to cause cancer or other serious health effects.

EPA’s 188 hazardous air pollutants include – Benzene (motor fuel, oil refineries, chemical processes) – Perchlorethylene (dry cleaning, degreasing) – Chloroform (solvent in adhesive and pesticides, by-product of chlorination processes) – BTEX, Dioxins, PAHs, Metals (Hg, Cr)

Area/ Other 25% Mobile (nonroad) 20%

National air toxics emissions sources in 1996 U.S. Environmental Protection Agency, 1998

Point 24% Mobile (onroad) 31%

Section 7 – Chemical Aspects of Air Pollution 9

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Basic Pollutants – Toxics

(2 of 2)

• Differences between toxics and criteria pollutants

– Health criteria are different • No AQI-like standards for toxics • Cancer/non-cancer benchmarks (long-term exposures) • Short-term exposure limits for some – A challenge to monitor • Usually not available in real-time • Example: Dioxin requires 28 days of sampling to acquire measurable amounts in ambient air – Often localized near source Section 7 – Chemical Aspects of Air Pollution 10

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Basic Pollutants – Sources

(1 of 4)

• Combustion • Evaporation • Natural Production

Section 7 – Chemical Aspects of Air Pollution 11

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Basic Pollutants – Sources

(2 of 4) Combustion • Complete combustion Fuel  water and carbon dioxide (CO 2 ) • Incomplete combustion Fuel  water, CO 2 , and other pollutants Pollutants are both gases and particles Section 7 – Chemical Aspects of Air Pollution 12

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Basic Pollutants – Sources

(3 of 4) Evaporation • Thousands of chemical compounds • Liquids evaporating or gases being released • Some harmful by themselves, some react to produce other pollutants • Many items you can smell are evaporative pollutants – Gasoline – benzene (sweet odor, toxic, carcinogenic) – Bleach – chlorine (toxic, greenhouse gas) – Trees – pinenes, limonene (ozone- and particulate matter forming) – Paint – volatile organic compounds (ozone- and particulate matter forming) – Baking bread, fermenting wine and beer – VOCs and ethanol (ozone-forming) Section 7 – Chemical Aspects of Air Pollution 13

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Basic Pollutants – Sources

(4 of 4)

Natural Production

• Fires (combustion) produce gases and particles • Winds “pick up” dust, dirt, sand and create particles of various sizes • Biosphere emits gases from trees, plants, soil, ocean, animals, microbes • Volcanoes and oil seeps produce particles and gases Section 7 – Chemical Aspects of Air Pollution 14

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Ozone

• Colorless gas • Composed of three oxygen atoms

– Oxygen molecule (O 2 ) —needed to sustain life – Ozone (O 3 ) —the extra oxygen atom makes ozone very reactive

• Secondary pollutant that forms from precursor gases

– Nitric oxide – combustion product – Volatile organic compounds (VOCs) – evaporative and combustion products Section 7 – Chemical Aspects of Air Pollution 15

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Solar radiation and chemistry

• The reaction that produces ozone in the atmosphere: O + O 2 + M  O 3 + M • Difference between stratospheric and tropospheric ozone generation is in the source of atomic O • For solar radiation with a wavelength of less than 242 nm: O 2 + hv  O + O Section 7 – Chemical Aspects of Air Pollution 16

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Solar radiation and chemistry

• Photochemical production of O 3 in troposphere tied to NO x NO 2 ) • For wavelengths less than 424 nm: NO • But NO will react with O 3 2 +

hv

 NO + O NO + O 3  NO 2 (NO + • Cycling has no net effect on ozone Section 7 – Chemical Aspects of Air Pollution 17

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Tropospheric Ozone Photolysis

Troposphere ozone photolysis takes place in a narrow UV window (300-320 nm), NO2 broadly below 428

30 o equinox midday Solar spectrum

Section 7 – Chemical Aspects of Air Pollution 18

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Nitrogen Oxides

● ● ● ● ● Nitrogen oxides, or NO x , is the generic term for a group of highly reactive gases, all of which contain nitrogen and oxygen in varying amounts. Nitrogen dioxide is most visually prominent (it is the yellow brown color in smog) The primary man-made sources of NO x are motor vehicles; electric utilities; and other industrial, commercial, and residential sources that burn fuels Affects the respiratory system Involved in other pollutant chemistry – One of the main ingredients in the formation of ground-level ozone – Reacts to form nitrate particles, acid aerosols, and NO 2 , which also cause respiratory problems – Contributes to the formation of acid rain (deposition) Section 7 – Chemical Aspects of Air Pollution 19

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Must make NO

2

• To make significant amounts of ozone must have a way to make NO 2 without consuming ozone • Presence of peroxy radicals, from the oxidation of hydrocarbons, disturbs O 3 -NO-NO 2 cycle NO + HO 2 ·  NO 2 + OH· NO + RO 2 ·  NO 2 + RO· – leads to net production of ozone Section 7 – Chemical Aspects of Air Pollution 20

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The Hydroxyl Radical

• produced from ozone photolysis – for radiation with wavelengths less than 320 nm: O 3 + hv  O( 1 D) + O 2 followed by O( 1 D) + M  O( 3 P) + M (+O 2  O 3 ) (~90%) O( 1 D) + H 2 O  2 OH· (~10%) • OH initiates the atmospheric oxidation of a wide range of compounds in the atmosphere – referred to as ‘detergent of the atmosphere’ – typical concentrations near the surface ~10 – very reactive, effectively recycled 6 - 10 7 cm -3 Section 7 – Chemical Aspects of Air Pollution 21

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THE OH RADICAL: MAIN TROPOSPHERIC OXIDANT

• Primary source: • O 3 + hn  O 2 • O( 1 D) + M  + O(1D) O + M • O( 1 D) + H 2 O  2OH (1) (2) (3) • Sink: oxidation of reduced species –leads to HO2(RO2) production • CO + OH • CH 4  + OH  CO 2 CH 3 + H + H 2 O • HCFC + OH

Major OH sinks

• Global Mean [OH] = 1.0x10

6 cm -3 molecules Section 7 – Chemical Aspects of Air Pollution 22

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Oxidation of CO - production of ozone

CO + OH· H· + O 2  + M  CO 2 HO 2 + H· · + M NO + HO 2 ·  NO 2 +

hv

 NO 2 + OH· NO + O O + O 2 + M  O 3 CO + 2 O 2 +

hv

 CO 2 + O 3 Section 7 – Chemical Aspects of Air Pollution 23

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Carbon Monoxide

• Odorless, colorless gas • Caused by incomplete combustion of fuel • Most of it comes from motor vehicles • Reduces the transport of oxygen through the bloodstream • Affects mental functions and visual acuity, even at low levels

Section 7 – Chemical Aspects of Air Pollution 24

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What breaks the cycle?

• Cycle terminated by OH· + NO 2  HO 2 · + HO 2 ·  HNO 3 H 2 O 2 • Both HNO 3 and H 2 O 2 will photolyze or react with OH to, in effect, reverse these pathways – but reactions are slow (lifetime of several days) – both are very soluble - though H 2 O 2 • washout by precipitation • dry deposition – in PBL they are effectively a loss less-so – situation is more complicated in the upper troposphere • no dry deposition, limited wet removal Section 7 – Chemical Aspects of Air Pollution 25

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Ozone Chemistry

Summary of ozone chemistry

Meteorology

• NO 2 + Sunlight • O+ O 2  O 3  NO + O Production Production

Chemistry Emissions

• NO + O 3  NO 2 • VOC + OH  + O2 Destruction RO 2 + H 2 O Production of NO 2 • RO 2 + NO  NO 2 + RO Destruction of O 3 without the RO=Reactive Organic compound such as VOC Key processes • Ample sunlight (ultraviolet) • High concentrations of precursors (VOC, NO, NO 2 ) – Weak horizontal dispersion – Weak vertical mixing • Warm air Section 7 – Chemical Aspects of Air Pollution 26

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Day and Night Chemistry

Section 7 – Chemical Aspects of Air Pollution 27

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Ozone Precursor Emissions

(1 of 2) ● ● ● Man-made sources – Oxides of nitrogen (NO x ) through combustion – VOCs through combustion and numerous other sources Natural sources (biogenic) – VOCs from trees/vegetation – NO x from soils (Midwest fertilizer) Concentration depends on – Source location, density, and strength – Meteorology Section 7 – Chemical Aspects of Air Pollution

Emissions Meteorology Chemistry

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NO

x

EMISSIONS (Tg N yr

-1

) TO TROPOSPHERE

Stratosphere 0.2

Lightning 5.8

Soils 5.1

Fossil Fuel 23.1

Biomass Burning 5.2

Biofuel 2.2

Aircraft 0.5

Section 7 – Chemical Aspects of Air Pollution 29

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An example of gridded NO

x

emissions

Section 7 – Chemical Aspects of Air Pollution 30

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Mapping of Tropospheric NO

2

From the GOME satellite instrument (July 1996) Section 7 – Chemical Aspects of Air Pollution 31

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GOME Can Provide Info on Daily Info

Section 7 – Chemical Aspects of Air Pollution 32

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Lightning Flashes Seen from Space

DJF JJA

Section 7 – Chemical Aspects of Air Pollution 2000 data 33

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Global Budget of CO

Section 7 – Chemical Aspects of Air Pollution 34

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Satellite Observations of Biomass Fires (1997)

Section 7 – Chemical Aspects of Air Pollution 35

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Daily Los Angeles Emission (1987)

Gas Carbon monoxide Nitric oxide Nitrogen dioxide Nitrous acid Total NO

x

+HONO Sulfur dioxide Sulfur trioxide Total SO

x

Alkanes Alkenes Aldehydes Ketones Alcohols Aromatics Hemiterpenes Total ROGs Methane Total emission Emission (tons/day) 9796 754 129 6.5

889.5

109 4.5

113.5

1399 313 108 29 33 500 47 2429 904 14,132 Section 7 – Chemical Aspects of Air Pollution Percent of total 69.3

6.3

0.8

27.2

6.4

100 36

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Percent Emission by Source-LA

Source Category Stationary Mobile Total CO(g) 2 98 100 NO x (g) SO x (g) ROG 24 38 50 76 100 62 100 50 100 Section 7 – Chemical Aspects of Air Pollution Table 4.2

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Most Important Gases in Smog in Terms of Ozone Reactivity and Abundance

1.

m

- and

p

-Xylene 2. Ethene 3. Acetaldehyde 4. Toluene 5. Formaldehyde 6. 8.

i o

-Pentane 7. Propene -Xylene 9. Butane 10. Methylcyclopentane Section 7 – Chemical Aspects of Air Pollution Table 4.4

38

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Lifetimes of ROGs Against Chemical Loss in Urban Air

ROG Species

n

-Butane

trans

-2-butene Acetylene Formaldehyde Acetone Ethanol Toluene Isoprene Phot. OH -- -- 22 h HO 2 1000 y 18 y 52 m 4 y O NO 29 d 6.3 d 4 m 3 -- 7 h 3 d 6 h -- 2.5 y -- 1.8 h 2.5 y 2 d 23 d -- -- -- 9.6 d -- 19 h 9 h -- -- 34 m -- -- -- 6 y 4 d -- -- 33 d 5 m O 3 650 y 17 m 200 d 3200 y -- -- 200 d 4.6 h Table 4.3

Section 7 – Chemical Aspects of Air Pollution 39

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Summary

Section 7 – Chemical Aspects of Air Pollution 40

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Ozone Meteorology – Key Processes

• Dispersion (horizontal mixing) • Vertical mixing • Sunlight • Transport • Weather pattern • Geography • Diurnal • Season

Emissions Meteorology Chemistry

Section 7 – Chemical Aspects of Air Pollution 41

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Ozone Precursor Emissions

(2 of 2) S Wind speed (WS) Concentration  S/WS S Vertical mixing (VM) Concentration  S/VM ● Key processes – Source location, density, and strength – Dispersion (horizontal mixing) - wind speed – Vertical mixing - inversion Courtesy of New Jersey Department of Environmental Protection Section 7 – Chemical Aspects of Air Pollution 42

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Daily Variation

Section 7 – Chemical Aspects of Air Pollution 43

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Source/Receptor Regions in Los Angeles

0.3

0.2

0.1

Urban center

NO Central Los Angeles August 28, 1987 NO 2 O 3 0 0 6 12 Hour of day 18 24

Sub-urban

0.3

0.2

San Bernardino August 28, 1987 NO 2 0.1

0 0 NO 6 12 Hour of day 18 O 3 Section 7 – Chemical Aspects of Air Pollution Figure 4.10

44

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Ozone Isopleth Plot

0.25

0.2

0.15

0.1

0.05

0.4

0 0 0.5

1 ROG (ppmC) Contours are ozone (ppmv) Section 7 – Chemical Aspects of Air Pollution 1.5

2 Figure 4.9

45

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Europe (seasonal) Europe (8-h avg.) U.S.

(8-h avg.) U.S.

(1-h avg.) 0 20 40 60 80 100 120 ppbv preindustrial present background

Section 7 – Chemical Aspects of Air Pollution

Slide courtesy of D. Jacob

46

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EU/USA

GEOS-CHEM model, July 1997 North America Europe Asia

Section 7 – Chemical Aspects of Air Pollution

Li et al. [2002]

47

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Section 7 – Chemical Aspects of Air Pollution 48

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Particulate Matter

(1 of 3) ● ● ● ● ● ● ● ● ● Complex mixture of solid and liquid particles Composed of many different compounds Both a primary and secondary pollutant Sizes vary tremendously Forms in many ways Clean-air levels are < 5 µg/m 3 * Background concentrations can be higher due to dust and smoke Concentrations range from 0 to 500+ µg/m 3 * Ultra-fine fly-ash or carbon soot Health concerns – Can aggravate heart diseases – Associated with cardiac arrhythmias and heart attacks – Can aggravate lung diseases such as asthma and bronchitis – Can increase susceptibility to respiratory infection * 24-hour average Section 7 – Chemical Aspects of Air Pollution 49

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Particulate Matter

(2 of 3) Particles come in different shapes and sizes Particle sizes • Ultra-fine particles (<0.1 μm) • Fine particles (0.1 to 2.5 μm) • Coarse particles (2.5 to 10 μm)

PM 10

Crustal material Carbon chain agglomerates Section 7 – Chemical Aspects of Air Pollution 50

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Particulate Matter

(3 of 3) A clear (left) and dirty (right) PM filter Section 7 – Chemical Aspects of Air Pollution 51

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Particulate Matter Composition

(1 of 3) PM is composed of a mixture of primary and secondary compounds.

● Primary PM (directly emitted) – Suspended dust – Sea salt – Organic carbon – Elemental carbon – Metals from combustion – Small amounts of sulfate and nitrate ● Secondary PM (precursor gases that form PM in the atmosphere) – Sulfur dioxide (SO 2 ): forms sulfates – Nitrogen oxides (NO x ): forms nitrates – Ammonia (NH 3 ): forms ammonium compounds – Volatile organic compounds (VOCs): form organic carbon compounds Section 7 – Chemical Aspects of Air Pollution 52

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Particulate Matter Composition

(3 of 3) • • • • Most PM mass in urban and nonurban areas is composed of a combination of the following chemical components

Geological Material –

suspended dust consists mainly of oxides of Al, Si, Ca, Ti, Fe, and other metal oxides

Ammonium –

ammonium bisulfate, sulfate, and nitrate are most common

Sulfate –

results from conversion of SO 2 gas to sulfate-containing particles

Nitrate –

results from a reversible gas/particle equilibrium between ammonia (NH 3 ), nitric acid (HNO 3 ), and particulate ammonium nitrate • • • •

NaCl –

salt is found in PM near sea coasts and after de-icing materials are applied

Organic Carbon (OC)

and oxygen

–

consists of hundreds of separate compounds containing mainly carbon, hydrogen,

Elemental Carbon (EC)

black, often called soot.

–

composed of carbon without much hydrocarbon or oxygen. EC is

Liquid Water –

sulfates, ammonium, sodium, other inorganic ions, and some organic material absorb water vapor from the atmosphere soluble nitrates, Section 7 – Chemical Aspects of Air Pollution Chow and Watson (1997) 53

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PM Emissions Sources

(1 of 4) Point – generally a major facility emitting pollutants from identifiable sources (pipe or smoke stack). Facilities are typically permitted. Section 7 – Chemical Aspects of Air Pollution 54

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PM Emissions Sources

(2 of 4) Area – any low-level source of air pollution released over a diffuse area (not a point) such as consumer products, architectural coatings, waste treatment facilities, animal feeding operations, construction, open burning, residential wood burning, swimming pools, and charbroilers Section 7 – Chemical Aspects of Air Pollution 55

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PM Emissions Sources

(3 of 4) Mobile • On-road is any moving source of air pollution such as cars, trucks, motorcycles, and buses • Non-road sources include pollutants emitted by combustion engines on farm and construction equipment, locomotives, commercial marine vessels, recreational watercraft, airplanes, snow mobiles, agricultural equipment, and lawn and garden equipment Section 7 – Chemical Aspects of Air Pollution 56

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PM Emissions Sources

(4 of 4) Natural – biogenic and geogenic emissions from wildfires, wind blown dust, plants, trees, grasses, volcanoes, geysers, seeps, soil, and lightning Section 7 – Chemical Aspects of Air Pollution 57

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COMPOSITION OF PM2.5 IS HIGHLY VARIABLE (NARSTO PM ASSESSMENT)

Esther (1995-99) 4.6 ug m -3 Egbert (1994-99) 8.9 ug m -3 Abbotsford (1994-95) 7.8 ug m -3 Toronto (1997-99) 12.3 ug m -3 Sulfate Nitrate Ammonium Black carbon Organic carbon Soil Other St. A ndrews (1994-97) 5.3 ug m -3 Fresno (1988-89) 39.2 ug m -3 Quaker City OH (1999) 12.4 ug m -3 Kern Wildlife Refuge (1988-89) 23.3 ug m -3 Arendstville PA (1999) 10.4 ug m -3 Los Angeles (1995-96) 30.3 ug m -3 Mexico City - Netzahualcoyotl (1997) 55.4 ug m -3 Washington DC (1996-99) 14.5 ug m -3 Colorado Plateau (1996-99) 3.0 ug m -3 Mexico City - Pedregal (1997) Yorkville (1999) 24.6 ug m -3 14.7 ug m -3 Section 7 – Chemical Aspects of Air Pollution Atlanta (1999) 19.2 ug m -3 58

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ORIGIN OF THE ATMOSPHERIC AEROSOL Aerosol: dispersed condensed matter suspended in a gas Size range: 0.001

m

m (molecular cluster) to 100

m

m (small raindrop) Soil dust Sea salt Environmental importance: health (respiration), visibility, radiative balance, cloud formation, heterogeneous reactions, delivery of nutrients…

Section 7 – Chemical Aspects of Air Pollution 59

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Particulate Matter Chemistry

(1 of 4)

Coagulation:

Particles collide and stick together.

Condensation:

Gases condense onto a small solid particle to form a liquid droplet.

Cloud/Fog Processes:

Gases dissolve in a water droplet and chemically react. A particle exists when the water evaporates.

Sulfate

Chemical Reaction:

Gases react to form particles.

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Particulate Matter Composition

(2 of 3) PM contains many compounds

Primary Particles (directly emitted) Secondary Particles (from precursor gases) VOCs Carbon (Soot) Organic Carbon SO 2 Metals Crustal (soil,dust) Ammonium Sulfate

Composition of PM tells us about the sources and formation processes

Other (sea salt) Ammonium Nitrate Ammoni a NO x

Section 7 – Chemical Aspects of Air Pollution

Gas Particle

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Sulfur Dioxide

• Sulfur dioxide (SO 2 ) belongs to the family of sulfur oxide (SO x ) gases.

• Gases are formed when fuel containing sulfur (mainly coal and oil) is burned and during metal smelting and other industrial processes. • Affects the respiratory system • Reacts in the atmosphere to form acids, sulfates, and sulfites • Contributes to acid rain

Impact of low soil pH on agriculture in Victoria German sandstone statue, 1908, 1969

Section 7 – Chemical Aspects of Air Pollution

Low crown density of spruce trees

62

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Particulate Matter Chemistry

(2 of 4) ● ● ● ● ● ● Sulfate Chemistry

Heterogeneous Oxidation

Virtually all ambient sulfate (99%) is secondary, formed within the atmosphere from SO 2 during the summer.

About half of SO NO x 2 oxidation to sulfate occurs in the gas phase through photochemical oxidation in the daytime. and hydrocarbon emissions tend to enhance the photochemical oxidation rate.

Only a small fraction of cloud droplets deposit out as rain; most droplets evaporate and leave a sulfate residue or “convective debris”.

Typical conversion rate 1-10% per hour Husar (1999) At least half of SO 2 oxidation takes place in cloud droplets as air molecules react in clouds.

Within clouds, soluble pollutant gases, such as SO 2 , are scavenged by water droplets and rapidly oxidize to sulfate.

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Mechanisms of Converting S(IV) to S(VI)

Why is converting to S(VI) important?

It allows sulfuric acid to enter or form within cloud drops and aerosol particles, increasing their acidity Mechanisms 1. Gas-phase oxidation of SO 2 (g) to H 2 SO 4 (g) followed by condensation of H 2 SO 4 (g) 2. Dissolution of SO 2 (g) into liquid water to form H 2 SO 3 (aq) followed by aqueous chemical conversion of H 2 SO 3 (aq) and its dissociation products to H 2 SO 4 (aq) and its dissociation products.

Section 7 – Chemical Aspects of Air Pollution 64

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Section 7 – Chemical Aspects of Air Pollution 65

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Particulate Matter Chemistry

(3 of 4) ● ● ● ● Nitrate Chemistry NO 2 can be converted to nitric acid (HNO 3 ) by reaction with hydroxyl radicals (OH) during the day.

– The reaction of OH with NO 2 reaction with SO 2 . is about 10 times faster than the OH – The peak daytime conversion rate of NO 2 is about 10% to 50% per hour.

to HNO 3 in the gas phase During the nighttime, NO 2 is converted into HNO 3 reactions involving ozone and the nitrate radical. by a series of HNO 3 reacts with ammonia to form particulate ammonium nitrate (NH 4 NO 3 ).

Thus, PM nitrate can be formed at night and during the day; daytime photochemistry also forms ozone.

Section 7 – Chemical Aspects of Air Pollution 66

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Particulate Matter Chemistry

(4 of 4) Sources

Chemical Processes

Emissions

Mechanical

• Sea salt • Dust

Particles

• NaCl • Crustal PM Formation PM Transport/Loss Sample Collection gases condense onto particles cloud/fog processes

Combustion

• Motor vehicles • Industrial • Fires

Particles

• Soot • Metals • OC

Gases

• NO x • SO • NH 2 • VOCs 3

Other gaseous

• Biogenic • Anthropogenic

Gases

• VOCs • NH 3 • NO x

Meteorological Processes

Winds Temperature Solar radiation Vertical mixing condensation and coagulation photochemical production cloud/fog processes Clouds, fog Temperature Relative humidity Solar radiation transport sedimentation (dry deposition) wet deposition Winds Precipitation Measurement Issues • Inlet cut points • Vaporization of nitrate, H 2 O, VOCs • Adsorption of VOCs • Absorption of H 2 O Temperature Relative humidity Winds Section 7 – Chemical Aspects of Air Pollution 67

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Phenomena Aloft Pressure Pattern Winds and Transport Temperature Inversions Rain Moisture Temperature Clouds/Fog Season Emissions

No direct impact. No direct impact.

Particulate Matter Meteorology

How weather affects PM emissions, formation, and transport

PM Formation

No direct impact.

PM Transport/Loss

Ridges tend to produce conditions conducive for accumulation of PM ozone.

2.5

. Troughs tend to produce conditions conducive for dispersion and removal of PM and In mountain-valley regions, strong wintertime inversions and high PM altered by weak troughs. 2.5

levels may not be High PM 2.5

concentrations often occur during the approach of a trough from the west.

Strong surface winds tend to disperse PM 2.5

regardless of season. Strong winds can create dust which can increase PM 2.5

concentrations. No direct impact.

Reduces soil and fire emissions No direct impact.

Warm temperatures are associated with increased evaporative, biogenic, and power plant emissions, which act to increase PM 2.5

. Cold temperatures can also indirectly influence PM on winter nights).

2.5

concentrations (i.e., home heating No direct impact.

In general, stronger winds disperse pollutants, resulting in a less ideal mixture of pollutants for chemical reactions that produce PM 2.5

.

Inversions reduce vertical mixing and therefore increase chemical concentrations of precursors. Higher concentrations of precursors can produce faster, more efficient chemical reactions that produce PM 2.5

.

Rain can remove precursors of PM 2.5

.

Moisture acts to increase the production of secondary PM 2.5

including sulfates and nitrates. Photochemical reaction rates increase with temperature.

A strong inversion acts to limit vertical mixing allowing for the accumulation of PM 2.5

.

Rain can remove PM 2.5

. No direct impact.

Although warm surface temperatures are generally associated with poor air quality conditions, very warm temperatures can increase vertical mixing and dispersion of pollutants.

Warm temperatures may volatize Nitrates from a solid to a gas.

Very cold surface temperatures during the winter may produce strong surface-based inversions that confine pollutants to a shallow layer.

Forest fires, wood burning, agriculture burning, field tilling, windblown dust, road dust, and construction vary by season. Water droplets can enhance the formation of secondary PM 2.5

. Clouds can limit photochemistry, which limits photochemical production.

Convective clouds are an indication of strong vertical mixing, which disperses pollutants.

Section 7 – Chemical Aspects of Air Pollution which changes the amount of solar radiation available for photochemistry.

68

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ANNUAL MEAN PARTICULATE MATTER (PM) CONCENTRATIONS AT U.S. SITES, 1995-2000 NARSTO PM Assessment, 2003 PM10 (particles > 10

m

m) PM2.5 (particles > 2.5

m

m) Red circles indicate violations of national air quality standard: 50

m

g m -3 for PM10 15

m

g m -3 for PM2.5

Section 7 – Chemical Aspects of Air Pollution 69

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AEROSOL OPTICAL DEPTH (GLOBAL MODEL) Annual mean

Section 7 – Chemical Aspects of Air Pollution 70

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AEROSOL OBSERVATIONS FROM SPACE Biomass fire haze in central America yesterday (4/30/03) Fire locations in red Modis.gsfc.nasa.gov

Section 7 – Chemical Aspects of Air Pollution 71

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BLACK CARBON EMISSIONS

DIESEL DOMESTIC COAL BURNING BIOMASS BURNING

Section 7 – Chemical Aspects of Air Pollution

Chin et al. [2000]

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RADIATIVE FORCING OF CLIMATE, 1750-PRESENT IPCC [2001] “

Kyoto also failed to address two major pollutants that have an impact on warming: black soot and tropospheric ozone. Both are proven health hazards. Reducing both would not only address climate change, but also dramatically improve people's health

.” (George W. Bush, June 11 2001 Rose

Section 7 – Chemical Aspects of Air Pollution

Garden speech)

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Particles Impact Human Health and MORE

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EPA REGIONAL HAZE RULE: FEDERAL CLASS I AREAS TO RETURN TO “NATURAL” VISIBILITY LEVELS BY 2064 clean day moderately polluted day Acadia National Park

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ASIAN DUST INFLUENCE IN UNITED STATES Dust observations from U.S. IMPROVE network April 16, 2001 Asian dust in western U.S.

April 22, 2001 Asian dust in southeastern U.S.

Glen Canyon, AZ 0 2 4 6 8

m

g m -3

Section 7 – Chemical Aspects of Air Pollution

Clear day April 16, 2001: Asian dust!

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Aerosols Link Air Quality, Health and Climate:

Dirtier Air and a Dimmer Sun

Anderson et al., Science 2003 Smith et al., 2003

Section 7 – Chemical Aspects of Air Pollution

He et al., 2002

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