Urban Air Pollution Public and Environmental Health Concerns –Elevated levels of toxic compounds Regional and Global Impacts –Background Chemistry and Composition –Climate Joel Thornton, Asst. Professor ftp.atmos.washington.edu/thornton/atms501

Houston, TX Aug Smog – “Smoke” + “Fog” Coined due to reduced visibility associated with pollution episodes Major components: “invisible”: O 3, CO, SO 2 “visible”: PM (aerosols) + some gases (NO 2 ) Ingredients to Make Smog Sun (photochemistry) Stagnation Sources of NO x, SO 2, PM and VOC The Urban Smog Problem

Ozone Damage Needle damage (tip necrosis) is a common sign of ozone stress on pines. Often observed in forests downwind of major urban areas—Sierra Nevada, New England, Mexico City, etc.

Large Subset of U.S. Population Exposed 1-hr Avg O 3 < 125 ppb 8-hr Avg O 3 < 85 ppb 24-hr Avg PM 2.5 < 60  g/m 3 Annual Avg PM 2.5 < 15  g/m 3 U.S. NAAQS #of people living where NAAQS are not attained

8hr avg > 85 ppb 1hr avg > 125 ppb Violation of O 3 NAAQS By Region

Annual Average PM 2.5 in Urban Areas

Surface O 3 and Transport 90 th percentile O 3 concentrations for summers and mean 850hPa winds on days when O 3 > 90 th percentile Stagnation enhances chemistry Persistent stagnation in regions of strong subsidence: LA, Mexico City, Athens Air pollution is not just an urban problem

NO x = NO + NO 2 CO/VOC hv = uv-vis radiation Fossil Fuel Combustion and Use Biogenic Activity Evolution of NO x and O 3 in Nashville, TN June 1999 Chemical Production of O 3 : Main Ingredients

1. NO + O 3  NO 2 + O 2 k 1 2. NO 2 + hv  NO + O k 2 3. O + O 2 + M  O 3 k 3 predict NO + XO 2  NO 2 + XO implies Often (not always) Cycling of HO x And NO x Leads to NET O 3

Net O 3 Production NO 2 NO O3O3 h HO 2 CO 2 CO HO O3O3 O2O2 NO 2 NO O3O3 h The Null Cycle The Net O 3 Production Cycle

1.The rate limiting step in NET O 3 production is the conversion of NO to NO 2 by peroxy radicals. What is the rate expression for photochemical O 3 formation? 2.Ronald Regan famously noted that “trees pollute too”. What did he mean by this statement? Questions

In U.S. isoprene emissions > total anthropogenic hydrocarbon emissions + OH  RO 2 O2O2 [10 12 atoms C cm -2 s -1 ] GEIA Isoprene Emissions In July, Guenther, et al Important source of peroxy radicals: enhance O 3 production Biogenic VOC: Major role in O 3 /PM Pollution

Urban areas (mega-cities) are major point sources Courtesy of P. Weiss-Penzias and D. Jaffe, UWB Global pollution transport makes meeting own air quality standards more challenging Global Impacts of Urban Air Pollution CO - MOPPIT NO 2 - OMI

A vast majority of NO x is emitted at the surface, and most NO x is a result of human activity. Given that NO x catalyzes O 3 production, it is important to consider the global impact of anthropogenic NO x emissions. 1.NO x is removed from the atmosphere primarily by the reaction NO 2 + OH  HNO 3, k ~ 1x cm 3 molec -1 s -1 what is a typical lifetime for NO x w.r.t. this process? ([OH] ~ 1x10 6 molec cm 3 ) 2.Is this lifetime sufficient to allow NO x to be transported away from an urban area to the remote troposphere? 3.Do anthropogenic emissions of NO x reach the remote troposphere at all? Questions

+ OH  RO 2 O2O2 k ~ 1x cm 3 molec -1 s -1 CH 3 CH 2 CH 3 + OH  RO 2 + H 2 O k ~ 1x cm 3 molec -1 s -1 O2O2 1.An important biogenic hydrocarbon is isoprene. Isoprene is very reactive towards OH. Given that [Isoprene] ~ 1 ppb, and [propane] < ~ 1 ppb outside of Atlanta, would it make sense to try to regulate propane emissions to combat O 3 production?