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Section 7 Chemical Aspects of Air Pollution

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

2 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. , L.A. City Council adopts regulation controlling smoke Early 1900’s, automobile use increases. 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

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

5 Discovery of Ozone in Smog
1948: Arie Haagen-Smit ( ), 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

6 Section 7 – Chemical Aspects of Air Pollution
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

7 Basic Pollutants (2 of 3) Pollutant Abbreviation Type Carbon Monoxide
CO Primary Sulfur Dioxide SO2 Primary Ozone O3 Secondary Nitrogen Dioxide NO2 Secondary Hydrocarbon Compounds (also called VOCs – volatile organic compounds ) HC Primary & Secondary Particulate Matter PM Primary & Secondary Section 7 – Chemical Aspects of Air Pollution

8 Section 7 – Chemical Aspects of Air Pollution
Basic Pollutants (3 of 3) 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. 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) Toxics can cause cancer or other effects such as birth defects National air toxics emissions sources in 1996 U.S. Environmental Protection Agency, 1998 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 Section 7 – Chemical Aspects of Air Pollution

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

12 Basic Pollutants – Sources (2 of 4)
Combustion Complete combustion Fuel  water and carbon dioxide (CO2) Incomplete combustion Fuel  water, CO2, and other pollutants Pollutants are both gases and particles 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) 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 Volcanoes produce water vapor (most prevalent, ash or particles, and gasses (SO2, CO2, Hydrogen Sulfide, Hydrochloric acid) Section 7 – Chemical Aspects of Air Pollution

15 Section 7 – Chemical Aspects of Air Pollution
Ozone Colorless gas Composed of three oxygen atoms Oxygen molecule (O2)—needed to sustain life Ozone (O3) —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

16 Solar radiation and chemistry
The reaction that produces ozone in the atmosphere: O + O2 + M  O3 + 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: O2 + hv  O + O Section 7 – Chemical Aspects of Air Pollution

17 Solar radiation and chemistry
Photochemical production of O3 in troposphere tied to NOx (NO + NO2) For wavelengths less than 424 nm: NO2 + hv  NO + O But NO will react with O3 NO + O3  NO2 Cycling has no net effect on ozone Section 7 – Chemical Aspects of Air Pollution

18 Tropospheric Ozone Photolysis
Troposphere ozone photolysis takes place in a narrow UV window ( nm), NO2 broadly below 428 30o equinox midday Solar spectrum Section 7 – Chemical Aspects of Air Pollution

19 Section 7 – Chemical Aspects of Air Pollution
Nitrogen Oxides Nitrogen oxides, or NOx, 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 NOx 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 NO2, which also cause respiratory problems Contributes to the formation of acid rain (deposition) Section 7 – Chemical Aspects of Air Pollution

20 Section 7 – Chemical Aspects of Air Pollution
Must make NO2 To make significant amounts of ozone must have a way to make NO2 without consuming ozone Presence of peroxy radicals, from the oxidation of hydrocarbons, disturbs O3-NO-NO2 cycle NO + HO2·  NO2 + OH· NO + RO2·  NO2 + RO· leads to net production of ozone Section 7 – Chemical Aspects of Air Pollution

21 Section 7 – Chemical Aspects of Air Pollution
The Hydroxyl Radical produced from ozone photolysis for radiation with wavelengths less than 320 nm: O3 + hv  O(1D) + O2 followed by O(1D) + M  O(3P) + M (+O2O3) (~90%) O(1D) + H2O  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 ~ cm-3 very reactive, effectively recycled Section 7 – Chemical Aspects of Air Pollution

22 THE OH RADICAL: MAIN TROPOSPHERIC OXIDANT
Primary source: O3 + hn  O2 + O(1D) (1) O(1D) + M  O + M (2) O(1D) + H2O  2OH (3) Sink: oxidation of reduced species –leads to HO2(RO2) production CO + OH  CO2 + H CH4 + OH  CH3 + H2O HCFC + OH Global Mean [OH] = 1.0x106 molecules cm-3 Major OH sinks Section 7 – Chemical Aspects of Air Pollution

23 Oxidation of CO - production of ozone
CO + OH·  CO2 + H· H· + O2 + M  HO2· + M NO + HO2·  NO2 + OH· NO2 + hv  NO + O O + O2 + M  O3 CO + 2 O2 + hv  CO2 + O3 Section 7 – Chemical Aspects of Air Pollution

24 Section 7 – Chemical Aspects of Air Pollution
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

25 Section 7 – Chemical Aspects of Air Pollution
What breaks the cycle? Cycle terminated by OH· + NO2  HNO3 HO2· + HO2·  H2O2 Both HNO3 and H2O2 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 H2O2 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 Section 7 – Chemical Aspects of Air Pollution

26 Section 7 – Chemical Aspects of Air Pollution
Ozone Chemistry Summary of ozone chemistry NO2 + Sunlight  NO + O Production O+ O2  O3 Production NO + O3  NO2 + O Destruction VOC + OH  RO2 + H2O Production of NO2 without the RO2 + NO  NO2 + RO Destruction of O3 Emissions Chemistry Meteorology RO=Reactive Organic compound such as VOC Key processes Ample sunlight (ultraviolet) High concentrations of precursors (VOC, NO, NO2) Weak horizontal dispersion Weak vertical mixing Warm air Complicated Prod Dest Titration Section 7 – Chemical Aspects of Air Pollution

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

28 Ozone Precursor Emissions (1 of 2)
Man-made sources Oxides of nitrogen (NOx) through combustion VOCs through combustion and numerous other sources Natural sources (biogenic) VOCs from trees/vegetation NOx from soils (Midwest fertilizer) Concentration depends on Source location, density, and strength Meteorology Emissions Chemistry Meteorology Add evaporation and biogenics fn of temperature Section 7 – Chemical Aspects of Air Pollution

29 NOx 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 Section 7 – Chemical Aspects of Air Pollution

30 An example of gridded NOx emissions
Section 7 – Chemical Aspects of Air Pollution

31 Mapping of Tropospheric NO2
From the GOME satellite instrument (July 1996) Section 7 – Chemical Aspects of Air Pollution

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

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

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

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

36 Daily Los Angeles Emission (1987)
Gas Emission (tons/day) Percent of total Carbon monoxide Nitric oxide 754 Nitrogen dioxide 129 Nitrous acid 6.5 Total NOx+HONO Sulfur dioxide 109 Sulfur trioxide 4.5 Total SOx Alkanes 1399 Alkenes 313 Aldehydes 108 Ketones 29 Alcohols 33 Aromatics 500 Hemiterpenes 47 Total ROGs Methane Total emission 14, Section 7 – Chemical Aspects of Air Pollution

37 Percent Emission by Source-LA
Source Category CO(g) NOx(g) SOx(g) ROG Stationary Mobile Total Table 4.2 Section 7 – Chemical Aspects of Air Pollution

38 Section 7 – Chemical Aspects of Air Pollution
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. i-Pentane 7. Propene 8. o-Xylene 9. Butane 10. Methylcyclopentane Table 4.4 Section 7 – Chemical Aspects of Air Pollution

39 Lifetimes of ROGs Against Chemical Loss in Urban Air
ROG Species Phot. OH HO2 O NO3 O3 n-Butane h 1000 y 18 y 29 d 650 y trans-2-butene m 4 y 6.3 d 4 m 17 m Acetylene d y d Formaldehyde 7 h 6 h 1.8 h 2.5 y 2 d 3200 y Acetone 23 d 9.6 d Ethanol h Toluene h y 33 d 200 d Isoprene m d 5 m 4.6 h Table 4.3 Section 7 – Chemical Aspects of Air Pollution

40 Section 7 – Chemical Aspects of Air Pollution
Summary 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 Discussed first three dispersion, vertical mixing, and sunlight produce but transport moves around. Transport - winds move pollutants around Section 7 – Chemical Aspects of Air Pollution

42 Ozone Precursor Emissions (2 of 2)
Concentration  S/WS Wind speed (WS) S Courtesy of New Jersey Department of Environmental Protection Concentration  S/VM Vertical mixing (VM) Dispersion is 3d, Hoziz and vertical We will classify horizontal dispersion just as dispersion Vertical mixing is basically vertical dispersion Key processes Source location, density, and strength Dispersion (horizontal mixing) - wind speed Vertical mixing - inversion Section 7 – Chemical Aspects of Air Pollution

43 Section 7 – Chemical Aspects of Air Pollution
Daily Variation 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 center Sub-urban Section 7 – Chemical Aspects of Air Pollution

45 Section 7 – Chemical Aspects of Air Pollution
Ozone Isopleth Plot 0.32 0.08 0.24 NOx (ppmv) 0.16 Contours are ozone (ppmv) Figure 4.9 Section 7 – Chemical Aspects of Air Pollution

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

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

48 Section 7 – Chemical Aspects of Air Pollution

49 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/m3 * Background concentrations can be higher due to dust and smoke Concentrations range from 0 to 500+ µg/m3 * 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 Ultra-fine fly-ash or carbon soot * 24-hour average 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) PM10 Crustal material Carbon chain agglomerates Section 7 – Chemical Aspects of Air Pollution

51 Particulate Matter (3 of 3)
A clear (left) and dirty (right) PM filter Filter on the right = approximate concentration would be 100 to 150 ug/m3 over a 24-hr period. Section 7 – Chemical Aspects of Air Pollution

52 Particulate Matter Composition (1 of 3)
PM is composed of a mixture of primary and secondary compounds. Secondary PM (precursor gases that form PM in the atmosphere) Sulfur dioxide (SO2): forms sulfates Nitrogen oxides (NOx): forms nitrates Ammonia (NH3): forms ammonium compounds Volatile organic compounds (VOCs): form organic carbon compounds Primary PM (directly emitted) Suspended dust Sea salt Organic carbon Elemental carbon Metals from combustion Small amounts of sulfate and nitrate Section 7 – Chemical Aspects of Air Pollution

53 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 SO2 gas to sulfate-containing particles Nitrate – results from a reversible gas/particle equilibrium between ammonia (NH3), nitric acid (HNO3), and particulate ammonium nitrate 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 Chow and Watson (1997) 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. Point Sources: -annual air emissions equal to or exceeding a limit per year 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 Point Sources: -annual air emissions equal to or exceeding a limit per year 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 Point Sources: -annual air emissions equal to or exceeding a limit per year 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 Point Sources: -annual air emissions equal to or exceeding a limit per year Section 7 – Chemical Aspects of Air Pollution

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

59 ORIGIN OF THE ATMOSPHERIC AEROSOL
Aerosol: dispersed condensed matter suspended in a gas Size range: mm (molecular cluster) to 100 mm (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

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. 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. Section 7 – Chemical Aspects of Air Pollution

61 Particulate Matter Composition (2 of 3)
PM contains many compounds Primary Particles (directly emitted) Secondary Particles (from precursor gases) VOCs Carbon (Soot) Organic Carbon SO2 Metals Ammonium Sulfate Composition of PM tells us about the sources and formation processes Crustal (soil,dust) Ammonium Nitrate Other (sea salt) Ammonia Gas NOx Particle Section 7 – Chemical Aspects of Air Pollution

62 Section 7 – Chemical Aspects of Air Pollution
Sulfur Dioxide Sulfur dioxide (SO2) belongs to the family of sulfur oxide (SOx) 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 Section 7 – Chemical Aspects of Air Pollution

63 Particulate Matter Chemistry (2 of 4)
Sulfate Chemistry Virtually all ambient sulfate (99%) is secondary, formed within the atmosphere from SO2 during the summer. About half of SO2 oxidation to sulfate occurs in the gas phase through photochemical oxidation in the daytime. NOx and hydrocarbon emissions tend to enhance the photochemical oxidation rate. At least half of SO2 oxidation takes place in cloud droplets as air molecules react in clouds. Within clouds, soluble pollutant gases, such as SO2, 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 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 SO2(g) to H2SO4(g) followed by condensation of H2SO4(g) 2. Dissolution of SO2(g) into liquid water to form H2SO3(aq) followed by aqueous chemical conversion of H2SO3(aq) and its dissociation products to H2SO4(aq) and its dissociation products. Section 7 – Chemical Aspects of Air Pollution

65 Section 7 – Chemical Aspects of Air Pollution

66 Particulate Matter Chemistry (3 of 4)
Nitrate Chemistry NO2 can be converted to nitric acid (HNO3) by reaction with hydroxyl radicals (OH) during the day. The reaction of OH with NO2 is about 10 times faster than the OH reaction with SO2. The peak daytime conversion rate of NO2 to HNO3 in the gas phase is about 10% to 50% per hour. During the nighttime, NO2 is converted into HNO3 by a series of reactions involving ozone and the nitrate radical. HNO3 reacts with ammonia to form particulate ammonium nitrate (NH4NO3). Thus, PM nitrate can be formed at night and during the day; daytime photochemistry also forms ozone. Section 7 – Chemical Aspects of Air Pollution

67 Particulate Matter Chemistry (4 of 4)
Sources Sample Collection PM Transport/Loss PM Formation Emissions Chemical Processes Mechanical Sea salt Dust Combustion Motor vehicles Industrial Fires Other gaseous Biogenic Anthropogenic Particles NaCl Crustal Soot Metals OC Gases NOx SO2 VOCs NH3 gases condense onto particles cloud/fog processes Measurement Issues Inlet cut points Vaporization of nitrate, H2O, VOCs Adsorption of VOCs Absorption of H2O transport sedimentation (dry deposition) wet deposition condensation and coagulation photochemical production cloud/fog processes Meteorological Processes Winds Clouds, fog Temperature Precipitation Relative humidity Solar radiation Vertical mixing Section 7 – Chemical Aspects of Air Pollution

68 Particulate Matter Meteorology
How weather affects PM emissions, formation, and transport Phenomena Emissions PM Formation PM Transport/Loss Aloft Pressure Pattern No direct impact. Ridges tend to produce conditions conducive for accumulation of PM2.5. Troughs tend to produce conditions conducive for dispersion and removal of PM and ozone. In mountain-valley regions, strong wintertime inversions and high PM2.5 levels may not be altered by weak troughs. High PM2.5 concentrations often occur during the approach of a trough from the west. Winds and Transport In general, stronger winds disperse pollutants, resulting in a less ideal mixture of pollutants for chemical reactions that produce PM2.5. Strong surface winds tend to disperse PM2.5 regardless of season. Strong winds can create dust which can increase PM2.5 concentrations. Temperature Inversions Inversions reduce vertical mixing and therefore increase chemical concentrations of precursors. Higher concentrations of precursors can produce faster, more efficient chemical reactions that produce PM2.5. A strong inversion acts to limit vertical mixing allowing for the accumulation of PM2.5. Rain Reduces soil and fire emissions Rain can remove precursors of PM2.5. Rain can remove PM2.5. Moisture Moisture acts to increase the production of secondary PM2.5 including sulfates and nitrates. Temperature Warm temperatures are associated with increased evaporative, biogenic, and power plant emissions, which act to increase PM2.5. Cold temperatures can also indirectly influence PM2.5 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/Fog Water droplets can enhance the formation of secondary PM2.5. Clouds can limit photochemistry, which limits photochemical production. Convective clouds are an indication of strong vertical mixing, which disperses pollutants. Season Forest 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. Section 7 – Chemical Aspects of Air Pollution

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

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

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

73 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 Rose Garden speech) Section 7 – Chemical Aspects of Air Pollution

74 Particles Impact Human Health and MORE

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

76 Asian dust in western U.S. Asian dust in southeastern U.S.
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. mg m-3 Glen Canyon, AZ Section 7 – Chemical Aspects of Air Pollution April 16, 2001: Asian dust! Clear day

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


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