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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. The Urban Smog Problem. Major components:

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Urban air pollution
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


The urban smog problem
The Urban Smog Problem

  • Major components:

  • “invisible”: O3, CO, SO2

  • “visible”: PM (aerosols) + some gases (NO2)

  • Ingredients to Make Smog

  • Sun (photochemistry)

  • Stagnation

  • Sources of NOx, SO2, PM and VOC

  • Smog – “Smoke” + “Fog”

  • Coined due to reduced visibility associated with pollution episodes

Houston, TX

Aug. 2000


Ozone damage
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
Large Subset of U.S. Population Exposed

#of people living where NAAQS are not attained

U.S. NAAQS

1-hr Avg O3 < 125 ppb

8-hr Avg O3 < 85 ppb

24-hr Avg PM2.5 < 60 g/m3

Annual Avg PM2.5 < 15 g/m3


Violation of o 3 naaqs by region
Violation of O3 NAAQS By Region

1hr avg > 125 ppb

8hr avg > 85 ppb


Annual average pm 2 5 in urban areas
Annual Average PM2.5 in Urban Areas


Surface o 3 and transport
Surface O3 and Transport

90th percentile O3 concentrations for summers 1991-1995 and mean 850hPa winds on days when O3 > 90th percentile

  • Stagnation enhances chemistry

  • Persistent stagnation in regions of strong subsidence: LA, Mexico City, Athens

  • Air pollution is not just an urban problem


  • Chemical production of o 3 main ingredients
    Chemical Production of O3: Main Ingredients

    Fossil Fuel Combustion and Use

    Evolution of NOx and O3 in Nashville, TN June 1999

    NOx = NO + NO2

    CO/VOC

    hv = uv-vis radiation

    Biogenic Activity


    Cycling of ho x and no x leads to net o 3
    Cycling of HOx And NOx Leads to NET O3

    1. NO + O3 NO2 + O2 k1

    2. NO2 + hv  NO + O k2

    3. O + O2 + M  O3 k3

    predict

    Often (not always)

    implies

    NO + XO2 NO2 + XO


    Net o 3 production
    Net O3 Production

    The Null Cycle

    NO2

    O2

    hn

    O3

    NO

    O3

    The Net O3 Production Cycle

    HO

    CO

    NO2

    hn

    HO2

    O3

    NO

    CO2


    Questions
    Questions

    • The rate limiting step in NET O3 production is the conversion of NO to NO2 by peroxy radicals. What is the rate expression for photochemical O3 formation?

    • Ronald Regan famously noted that “trees pollute too”. What did he mean by this statement?


    Biogenic voc major role in o 3 pm pollution
    Biogenic VOC: Major role in O3/PM Pollution

    O2

    Important source of peroxy radicals: enhance O3 production

    + OH  RO2

    In U.S. isoprene emissions > total anthropogenic hydrocarbon emissions

    GEIA Isoprene Emissions

    In July, Guenther, et al

    [1012 atoms C cm-2 s-1]


    Global impacts of urban air pollution
    Global Impacts of Urban Air Pollution

    CO - MOPPIT

    Urban areas (mega-cities) are major point sources

    NO2 - OMI

    Courtesy of P. Weiss-Penzias and D. Jaffe, UWB

    Global pollution transport makes meeting own air quality standards more challenging


    Questions1
    Questions

    • A vast majority of NOx is emitted at the surface, and most NOx is a result of human activity. Given that NOx catalyzes O3 production, it is important to consider the global impact of anthropogenic NOx emissions.

    • NOx is removed from the atmosphere primarily by the reaction NO2 + OH  HNO3, k ~ 1x10-11 cm3 molec-1 s-1 what is a typical lifetime for NOx w.r.t. this process? ([OH] ~ 1x106 molec cm3)

    • Is this lifetime sufficient to allow NOx to be transported away from an urban area to the remote troposphere?

    • Do anthropogenic emissions of NOx reach the remote troposphere at all?


    Questions2
    Questions

    • 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 O3 production?

    O2

    k ~ 1x10-11 cm3 molec-1 s-1

    + OH  RO2

    O2

    k ~ 1x10-13 cm3 molec-1 s-1

    CH3CH2CH3 + OH  RO2 + H2O


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