1. ATS 621 Fall 2012 Lecture 14

2. SMOG (Sulfurous vs. Photochemical Pollution) Example: London (also Eastern US) smoke + fog SO 2 + “soot”, sulfuric acid particles characterized by inversions, cool weather, coal burning Example: LA UV, hydrocarbons, NOx characterized by hot dry sunny weather, reduced visibility and high oxidant levels  We will be focusing on this kind!

4. The 1948 Donora smog was a historic air inversion resulting in a wall of smog that killed 20 people and sickened 7,000 more in Donora, Pennsylvania, a mill town on the Monongahela River, 24 miles (39 km) southeast of Pittsburgh. A severe smog event in London in 1952 was the event that finally sharply focused attention on the growing importance of severe air quality impairment….

5. GREAT LONDON SMOG OF 1952 Dec 5-9, 1952 Cold fog + (high sulfur) coal + diesel buses = “pea souper” Killed 4000 people (young & elderly), and over 8000 died subsequently Clean Air Acts of 1956 and 1968 and City of London Act of 1954. Smog = fog intensified by smoke (Henry Antoine Des Voeux, who first used it in 1905 to describe British urban areas) http://www.martinfrost.ws/htmlfiles/great_smog.html Monet painting showing Victorian smog (1900) [Baker and Thornes, 2006] http://www.feast.org/articles/?ID=331

6. First vapor recovery nozzles (1978) “During the 1950s and 1960s, Southern California air quality officials tackled myriad pollution sources: petroleum- based solvents containing hydrocarbons, landfills emitting toxic gases, power plants emitting nitrogen oxides, even rendering plants that processed animal wastes. Air quality regulations significantly reduced emissions, but peak ozone levels remained extremely high -- more than four times the current health standard. Regulators knew they needed to go after the prime source -- the motor vehicle.”

8. National Ambient Air Quality Standards

17. 1996-2005 NO x EMISSION TREND SEEN FROM SPACE [Van der A et al., 2008]

18. POWER PLANT EMISSION REDUCTIONS IN THE EASTERN US Effects of NO x controls on large point sources in the Eastern US beginning in the late 1990s Acid Rain Program, NO x SIP Call, NO x Budget Trading Program Focus on coal-burning power plants Improved burner technology, post-burner ammonia scrubbers Ohio River Valley 1997 E(NO x ) ~ 50% power plant Northeast Urban Corridor E(NO x ) < 20% power plant Ohio River Valley 2005 E(NO x ) ~ 20% power plant Courtesy: Greg Frost (NOAA) [Kim et al., 2006]

19. POWER PLANT POINT SOURCES IN WESTERN US SEEN FROM SPACE North Valmy Intermountain Hunter / Huntington Mohave Navajo Four Corners/ San Juan Cholla/Coronado/ Springerville Bonanza Craig/Hayden Jim Bridger/ Naughton Dave Johnston/ Laramie River Colstrip Reid Gardener Courtesy: Greg Frost (NOAA) [Kim et al., 2009]

20. U.S. GROWTH MEASURES (2008)

26. OZONE/PM EXPOSURE DEGRADES HEALTH Unscheduled hospital visits for asthma medication increases with ozone [Environmental Working Group Report, 2005] In California alone… In 1997 EPA estimated that particulate air emissions cause 35,000 premature deaths each year.

27. OZONE IMPACTS ON VEGETATION SUM06 Index: ozone dose in excess of 60 ppb during growing season Documented negative effects 1995 data

29. THE NEW OZONE STANDARD CAUSES MORE U.S. AREAS TO BE OUT OF COMPLIANCE

30. U.S. EMISSIONS OF OZONE PRECURSORS and trends over past 20 years Anthropogenic VOCs Fuel combustion vehicles power plants Fuel combustion & transport Solvents Vehicles Fires Isoprene (biogenic VOC) Vegetation Flat/down Down 30% Down 40% Flat

31. A “typical” smoggy day

34. 75 ppb (new standard, set in 2008) OZONE AND PARTICULATE MATTER (PM): THE TOP TWO AIR POLLUTANTS IN THE U.S. 15  g m -3 (annual), 35 (daily)

35. OZONE PRODUCTION IN TROPOSPHERE Photochemical oxidation of CO and volatile organic compounds (VOCs) catalyzed by hydrogen oxide radicals (HO x ) in the presence of nitrogen oxide radicals (NO x ) HO x = H + OH + HO 2 + RO + RO 2 NO x = NO + NO 2 Oxidation of CO: Oxidation of VOC: RO can also decompose or isomerize; range of carbonyl products Carbonyl products can react with OH to produce additional ozone, or photolyze to generate more HO x radicals (branching reaction) OH can also add to double bonds of unsaturated VOCs

36. OXIDATION OF HYDROCARBONS CONTRIBUTE TO OZONE FORMATION IN POLLUTED AIR Alkenes: OH oxidation adds to double bond (does not abstract H as with alkanes). With double bond, alkenes can also be oxidized by ozone Aromatics (with benzene rings): reactive with OH, via either addition or abstraction  source of secondary organic aerosol (SOA) RH RO 2 ROOH RO R’CHO OR R’C(O)R” NO HO 2 O 2 isom decomp hv R O2O2 alkyl radical alkylperoxy radical alkoxy radical OH aldehyde ketone Additional oxidation by NO 3 (but only at night!) > C4: RONO 2 NO < C4: alkyl nitrates NO 2 HO 2 Generic Alkane OH Oxidation Scheme (no longer just CO and CH 4 !) Can photolyze to produce HOx or react with OH to continue chain… NO 2 RO 2 NO 2 org nitrates

37. General rules for atmospheric oxidation of hydrocarbons Attack by OH is by H abstraction for saturated HCs (alkanes), by addition for unsaturated HCs (alkenes) Reactivity increases with number of C-H bonds, number of unsaturated bonds Organic radicals other than peroxy react with O 2 (if they are small) or decompose (if they are large); O 2 addition produces peroxy radicals. Organic peroxy radicals (RO 2 ) react with NO and HO 2 (dominant), other RO 2 (minor); they also react with NO 2 but the products decompose rapidly (except in the case of peroxyacyl radicals which produce peroxyacylnitrates or PANs) RO 2 +HO 2 produces organic hydroperoxides ROOH, RO 2 +NO produces carbonyls (aldehydes RCHO and ketones RC(O)R’) Carbonyls and hydroperoxides can photolyze (radical source) as well as react with OH Unsaturated HCs can also react with ozone, producing carbonyls and carboxylic acids RO 2 +R’O 2 reactions produce a range of oxygenated organic compounds including carbonyls, carboxylic acids, alcohols, esters…

38. OZONE CONCENTRATIONS vs. NO x AND VOC EMISSIONS Air pollution model calculation for a typical urban airshed NO x -saturated (or HC limited) NO x -limitedRidge

39. Extras

40. GOOD AND BAD OZONE Stratosphere: O 2 + UV sunlight = O + O O + O 2  O 3 Troposphere: CO + NOx + sunlight  O 3 VOCs