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AREP GAW Section 7 Chemical Aspects of Air Pollution Overview of Basic Pollutants Ozone Particulate Matter Carbon Monoxide Sulfur Dioxide Nitrogen Oxides.

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Presentation on theme: "AREP GAW Section 7 Chemical Aspects of Air Pollution Overview of Basic Pollutants Ozone Particulate Matter Carbon Monoxide Sulfur Dioxide Nitrogen Oxides."— Presentation transcript:

1 AREP GAW Section 7 Chemical Aspects of Air Pollution Overview of Basic Pollutants Ozone Particulate Matter Carbon Monoxide Sulfur Dioxide Nitrogen Oxides

2 AREP GAW Section 7 – Chemical Aspects of Air Pollution 2

3 AREP GAW Section 7 – Chemical Aspects of Air Pollution 3 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 1900s, 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.

4 AREP GAW Section 7 – Chemical Aspects of Air Pollution 4 Los Angeles, California (December 3, 1909) Library of Congress Prints and Photographs Division, Washington, D. C.

5 AREP GAW Section 7 – Chemical Aspects of Air Pollution 5 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.

6 AREP GAW Section 7 – Chemical Aspects of Air Pollution 6 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

7 AREP GAW Section 7 – Chemical Aspects of Air Pollution 7 PrimarySO 2 Sulfur Dioxide Primary & SecondaryPMParticulate Matter Primary & SecondaryHC Hydrocarbon Compounds (also called VOCs – volatile organic compounds ) SecondaryNO 2 Nitrogen Dioxide SecondaryO3O3 Ozone PrimaryCOCarbon Monoxide TypeAbbreviationPollutant Basic Pollutants (2 of 3)

8 AREP GAW Section 7 – Chemical Aspects of Air Pollution 8 Basic Pollutants (3 of 3)

9 AREP GAW Section 7 – Chemical Aspects of Air Pollution 9 Basic Pollutants – Toxics (1 of 2) Air toxics (hazardous air pollutants) are known or suspected to cause cancer or other serious health effects. EPAs 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) National air toxics emissions sources in 1996 U.S. Environmental Protection Agency, 1998

10 AREP GAW Section 7 – Chemical Aspects of Air Pollution 10 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

11 AREP GAW Section 7 – Chemical Aspects of Air Pollution 11 Basic Pollutants – Sources (1 of 4) Combustion Evaporation Natural Production

12 AREP GAW Section 7 – Chemical Aspects of Air Pollution 12 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

13 AREP GAW Section 7 – Chemical Aspects of Air Pollution 13 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)

14 AREP GAW Section 7 – Chemical Aspects of Air Pollution 14 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

15 AREP GAW Section 7 – Chemical Aspects of Air Pollution 15 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

16 AREP GAW Section 7 – Chemical Aspects of Air Pollution 16 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

17 AREP GAW Section 7 – Chemical Aspects of Air Pollution 17 Solar radiation and chemistry Photochemical production of O 3 in troposphere tied to NO x (NO + NO 2 ) For wavelengths less than 424 nm: NO 2 + hv NO + O But NO will react with O 3 NO + O 3 NO 2 Cycling has no net effect on ozone

18 AREP GAW Section 7 – Chemical Aspects of Air Pollution 18 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

19 AREP GAW Section 7 – Chemical Aspects of Air Pollution 19 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)

20 AREP GAW Section 7 – Chemical Aspects of Air Pollution 20 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

21 AREP GAW Section 7 – Chemical Aspects of Air Pollution 21 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 6 - 10 7 cm -3 –very reactive, effectively recycled

22 AREP GAW Section 7 – Chemical Aspects of Air Pollution 22 THE OH RADICAL: MAIN TROPOSPHERIC OXIDANT Primary source: O 3 + hn O 2 + O(1D)(1) O( 1 D) + M O + M(2) O( 1 D) + H 2 O 2OH(3) Sink: oxidation of reduced species –leads to HO2(RO2) production CO + OH CO 2 + H CH 4 + OH CH 3 + H 2 O HCFC + OH Global Mean [OH] = 1.0x10 6 molecules cm -3 Major OH sinks

23 AREP GAW Section 7 – Chemical Aspects of Air Pollution 23 Oxidation of CO - production of ozone CO + OH· CO 2 + H· H· + O 2 + M HO 2 · + M NO + HO 2 · NO 2 + OH· NO 2 + hv NO + O O + O 2 + M O 3 CO + 2 O 2 + hv CO 2 + O 3

24 AREP GAW Section 7 – Chemical Aspects of Air Pollution 24 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

25 AREP GAW Section 7 – Chemical Aspects of Air Pollution 25 What breaks the cycle? Cycle terminated by OH· + NO 2 HNO 3 HO 2 · + HO 2 · 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 less-so washout by precipitation dry deposition –in PBL they are effectively a loss –situation is more complicated in the upper troposphere no dry deposition, limited wet removal

26 AREP GAW Section 7 – Chemical Aspects of Air Pollution 26 Ozone Chemistry Summary of ozone chemistry NO 2 + Sunlight NO + O Production O+ O 2 O 3 Production NO + O 3 NO 2 + O2 Destruction VOC + OH RO 2 + H 2 OProduction of NO 2 without the RO 2 + NO NO 2 + RODestruction of O 3 Emissions Chemistry Meteorology Key processes Ample sunlight (ultraviolet) High concentrations of precursors (VOC, NO, NO 2 ) –Weak horizontal dispersion –Weak vertical mixing Warm air RO=Reactive Organic compound such as VOC

27 AREP GAW Section 7 – Chemical Aspects of Air Pollution 27 Day and Night Chemistry

28 AREP GAW Section 7 – Chemical Aspects of Air Pollution 28 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 Emissions Chemistry Meteorology

29 AREP GAW Section 7 – Chemical Aspects of Air Pollution 29 NO x EMISSIONS (Tg N yr -1 ) TO TROPOSPHERE Fossil Fuel 23.1 Aircraft 0.5 Biofuel 2.2 Biomass Burning 5.2 Soils 5.1 Lightning 5.8 Stratosphere 0.2

30 AREP GAW Section 7 – Chemical Aspects of Air Pollution 30 An example of gridded NO x emissions

31 AREP GAW Section 7 – Chemical Aspects of Air Pollution 31 Mapping of Tropospheric NO 2 From the GOME satellite instrument (July 1996)

32 AREP GAW Section 7 – Chemical Aspects of Air Pollution 32 GOME Can Provide Info on Daily Info

33 AREP GAW Section 7 – Chemical Aspects of Air Pollution 33 Lightning Flashes Seen from Space 2000 data DJF JJA

34 AREP GAW Section 7 – Chemical Aspects of Air Pollution 34 Global Budget of CO

35 AREP GAW Section 7 – Chemical Aspects of Air Pollution 35 Satellite Observations of Biomass Fires (1997)

36 AREP GAW Section 7 – Chemical Aspects of Air Pollution 36 Daily Los Angeles Emission (1987) GasEmission (tons/day) Percent of total Carbon monoxide 979669.3 Nitric oxide754 Nitrogen dioxide129 Nitrous acid6.5 Total NO x +HONO889.56.3 Sulfur dioxide 109 Sulfur trioxide4.5 Total SO x 113.50.8 Alkanes1399 Alkenes313 Aldehydes108 Ketones29 Alcohols33 Aromatics500 Hemiterpenes47 Total ROGs242927.2 Methane9046.4 Total emission14,132100

37 AREP GAW Section 7 – Chemical Aspects of Air Pollution 37 Percent Emission by Source-LA Table 4.2 Source CategoryCO(g)NO x (g)SO x (g)ROG Stationary2243850 Mobile98766250 Total100100100100

38 AREP GAW Section 7 – Chemical Aspects of Air Pollution 38 Most Important Gases in Smog in Terms of Ozone Reactivity and Abundance Table 4.4 1. m- and p-Xylene 2. Ethene 3. Acetaldehyde 4. Toluene 5. Formaldehyde 6. i-Pentane 7. Propene 8. o-Xylene 9. Butane 10. Methylcyclopentane

39 AREP GAW Section 7 – Chemical Aspects of Air Pollution 39 Lifetimes of ROGs Against Chemical Loss in Urban Air Table 4.3 ROG SpeciesPhot.OHHO 2 ONO 3 O 3 n-Butane---22 h1000 y18 y29 d650 y trans-2-butene---52 m4 y6.3 d4 m17 m Acetylene---3 d---2.5 y---200 d Formaldehyde7 h6 h1.8 h2.5 y2 d3200 y Acetone23 d9.6 d--- --------- Ethanol---19 h------------ Toluene---9 h--- 6 y33 d200 d Isoprene---34 m---4 d5 m4.6 h

40 AREP GAW Section 7 – Chemical Aspects of Air Pollution 40 Summary

41 AREP GAW Section 7 – Chemical Aspects of Air Pollution 41 Ozone Meteorology – Key Processes Dispersion (horizontal mixing) Vertical mixing Sunlight Transport Weather pattern Geography Diurnal Season Emissions Chemistry Meteorology

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

43 AREP GAW Section 7 – Chemical Aspects of Air Pollution 43 Daily Variation

44 AREP GAW Section 7 – Chemical Aspects of Air Pollution 44 Source/Receptor Regions in Los Angeles Volume mixing ratio (ppmv) Figure 4.10 Volume mixing ratio (ppmv) Urban centerSub-urban

45 AREP GAW Section 7 – Chemical Aspects of Air Pollution 45 Ozone Isopleth Plot Figure 4.9Contours are ozone (ppmv) NO x (ppmv) 0.24 0.08 0.32 0.16

46 AREP GAW Section 7 – Chemical Aspects of Air Pollution 46 Slide courtesy of D. Jacob

47 AREP GAW Section 7 – Chemical Aspects of Air Pollution 47 EU/USA

48 AREP GAW Section 7 – Chemical Aspects of Air Pollution 48

49 AREP GAW Section 7 – Chemical Aspects of Air Pollution 49 Particulate Matter (1 of 3) Ultra-fine fly-ash or carbon soot 24-hour average * 24-hour average 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 * 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

50 AREP GAW Section 7 – Chemical Aspects of Air Pollution 50 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 Carbon chain agglomeratesCrustal material

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

52 AREP GAW Section 7 – Chemical Aspects of Air Pollution 52 Particulate Matter Composition (1 of 3) 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 PM is composed of a mixture of primary and secondary compounds.

53 AREP GAW Section 7 – Chemical Aspects of Air Pollution 53 NaCl – salt is found in PM near sea coasts and after de-icing materials are applied Organic Carbon (OC) – consists of hundreds of separate compounds containing mainly carbon, hydrogen, and oxygen Elemental Carbon (EC) – composed of carbon without much hydrocarbon or oxygen. EC is black, often called soot. Liquid Water – soluble nitrates, sulfates, ammonium, sodium, other inorganic ions, and some organic material absorb water vapor from the atmosphere Particulate Matter Composition (3 of 3) Chow and Watson (1997) 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 Most PM mass in urban and nonurban areas is composed of a combination of the following chemical components

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

55 AREP GAW Section 7 – Chemical Aspects of Air Pollution 55 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

56 AREP GAW Section 7 – Chemical Aspects of Air Pollution 56 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

57 AREP GAW Section 7 – Chemical Aspects of Air Pollution 57 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

58 AREP GAW Section 7 – Chemical Aspects of Air Pollution 58 COMPOSITION OF PM2.5 IS HIGHLY VARIABLE (NARSTO PM ASSESSMENT)

59 AREP GAW Section 7 – Chemical Aspects of Air Pollution 59 ORIGIN OF THE ATMOSPHERIC AEROSOL Soil dust Sea salt Aerosol: dispersed condensed matter suspended in a gas Size range: 0.001 m (molecular cluster) to 100 m (small raindrop) Environmental importance: health (respiration), visibility, radiative balance, cloud formation, heterogeneous reactions, delivery of nutrients…

60 AREP GAW Section 7 – Chemical Aspects of Air Pollution 60 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. Chemical Reaction: Gases react to form particles. Cloud/Fog Processes: Gases dissolve in a water droplet and chemically react. A particle exists when the water evaporates. Sulfate

61 AREP GAW Section 7 – Chemical Aspects of Air Pollution 61 NO x Ammoni a VOCs Particulate Matter Composition (2 of 3) PM contains many compounds Primary Particles (directly emitted) Secondary Particles (from precursor gases) Other (sea salt) Other (sea salt) Crustal (soil,dust) Crustal (soil,dust) Organic Carbon Organic Carbon (Soot) Carbon (Soot) SO 2 Ammonium Sulfate Ammonium Sulfate Ammonium Nitrate Ammonium Nitrate Metals Composition of PM tells us about the sources and formation processes Gas Particle

62 AREP GAW Section 7 – Chemical Aspects of Air Pollution 62 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 Low crown density of spruce trees German sandstone statue, 1908, 1969 Impact of low soil pH on agriculture in Victoria

63 AREP GAW Section 7 – Chemical Aspects of Air Pollution 63 Sulfate Chemistry Virtually all ambient sulfate (99%) is secondary, formed within the atmosphere from SO 2 during the summer. About half of SO 2 oxidation to sulfate occurs in the gas phase through photochemical oxidation in the daytime. NO x and hydrocarbon emissions tend to enhance the photochemical oxidation rate. 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. 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) Heterogeneous Oxidation Particulate Matter Chemistry (2 of 4)

64 AREP GAW Section 7 – Chemical Aspects of Air Pollution 64 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.

65 AREP GAW Section 7 – Chemical Aspects of Air Pollution 65

66 AREP GAW Section 7 – Chemical Aspects of Air Pollution 66 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 is about 10 times faster than the OH reaction with SO 2. – The peak daytime conversion rate of NO 2 to HNO 3 in the gas phase is about 10% to 50% per hour. During the nighttime, NO 2 is converted into HNO 3 by a series of reactions involving ozone and the nitrate radical. 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.

67 AREP GAW Section 7 – Chemical Aspects of Air Pollution 67 WindsClouds, fogWindsTemperature PrecipitationRelative humidity Solar radiationRelative humidityWinds Vertical mixingSolar radiation condensation and coagulation photochemical production cloud/fog processes gases condense onto particles cloud/fog processes Measurement Issues Inlet cut points Vaporization of nitrate, H 2 O, VOCs Adsorption of VOCs Absorption of H 2 O transport sedimentation (dry deposition) wet deposition Mechanical Sea salt Dust Combustion Motor vehicles Industrial Fires Other gaseous Biogenic Anthropogenic Particles NaCl Crustal Particles Soot Metals OC Gases NO x SO 2 VOCs NH 3 Gases VOCs NH 3 NO x Sources Sample Collection PM Transport/Loss PM Formation Emissions Chemical Processes Meteorological Processes Particulate Matter Chemistry (4 of 4)

68 AREP GAW Section 7 – Chemical Aspects of Air Pollution 68 PhenomenaEmissionsPM FormationPM Transport/Loss Aloft Pressure Pattern No direct impact. Ridges tend to produce conditions conducive for accumulation of PM 2.5. Troughs tend to produce conditions conducive for dispersion and removal of PM and ozone. In mountain-valley regions, strong wintertime inversions and high PM 2.5 levels may not be altered by weak troughs. High PM 2.5 concentrations often occur during the approach of a trough from the west. Winds and Transport 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. Strong surface winds tend to disperse PM 2.5 regardless of season. Strong winds can create dust which can increase PM 2.5 concentrations. Temperature Inversions No direct impact.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. A strong inversion acts to limit vertical mixing allowing for the accumulation of PM 2.5. RainReduces soil and fire emissionsRain can remove precursors of PM 2.5. Rain can remove PM 2.5. MoistureNo direct impact.Moisture acts to increase the production of secondary PM 2.5 including sulfates and nitrates. No direct impact. TemperatureWarm 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 2.5 concentrations (i.e., home heating on winter nights). Photochemical reaction rates increase with temperature. 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. Clouds/FogNo direct impact.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. SeasonForest fires, wood burning, agriculture burning, field tilling, windblown dust, road dust, and construction vary by season. The sun angle changes with season, which changes the amount of solar radiation available for photochemistry. No direct impact. Particulate Matter Meteorology How weather affects PM emissions, formation, and transport

69 AREP GAW Section 7 – Chemical Aspects of Air Pollution 69 ANNUAL MEAN PARTICULATE MATTER (PM) CONCENTRATIONS AT U.S. SITES, 1995-2000 NARSTO PM Assessment, 2003 PM10 (particles > 10 m) PM2.5 (particles > 2.5 m) Red circles indicate violations of national air quality standard: 50 g m -3 for PM10 15 g m -3 for PM2.5

70 AREP GAW Section 7 – Chemical Aspects of Air Pollution 70 AEROSOL OPTICAL DEPTH (GLOBAL MODEL) Annual mean

71 AREP GAW Section 7 – Chemical Aspects of Air Pollution 71 AEROSOL OBSERVATIONS FROM SPACE Biomass fire haze in central America yesterday (4/30/03) Fire locations in red Modis.gsfc.nasa.gov

72 AREP GAW Section 7 – Chemical Aspects of Air Pollution 72 BLACK CARBON EMISSIONS Chin et al. [2000] DIESEL DOMESTIC COAL BURNING BIOMASS BURNING

73 AREP GAW Section 7 – Chemical Aspects of Air Pollution 73 RADIATIVE FORCING OF CLIMATE, 1750-PRESENT 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 Garden speech) IPCC [2001]

74 AREP GAW Particles Impact Human Health and MORE

75 AREP GAW Section 7 – Chemical Aspects of Air Pollution 75 EPA REGIONAL HAZE RULE: FEDERAL CLASS I AREAS TO RETURN TO NATURAL VISIBILITY LEVELS BY 2064 Acadia National Park clean day moderately polluted day http://www.hazecam.net/ …will require essentially total elimination of anthropogenic aerosols!

76 AREP GAW Section 7 – Chemical Aspects of Air Pollution 76 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 Clear day April 16, 2001: Asian dust! 0 2 4 6 8 g m -3

77 AREP GAW Section 7 – Chemical Aspects of Air Pollution 77 Aerosols Link Air Quality, Health and Climate: Dirtier Air and a Dimmer Sun Anderson et al., Science 2003Smith et al., 2003He et al., 2002


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