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Atmospheric Chemistry. Photochemical Pollutants - Ozone Formation and Degradation Global Warming Visibility. Dr. Steven Japar Ford Motor Co. – Retired March 29, 2005. TROPOSPHERIC CHEMISTRY John H. Seinfeld, Spyros N. Pandis, “Atmospheric Chemistry and Physics” (John Wiley & Sons, 1998).

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Atmospheric chemistry

Atmospheric Chemistry

  • Photochemical Pollutants - Ozone Formation and Degradation

  • Global Warming

  • Visibility

Dr. Steven Japar

Ford Motor Co. – Retired

March 29, 2005


Atmospheric chemistry

TROPOSPHERIC CHEMISTRYJohn H. Seinfeld, Spyros N. Pandis, “Atmospheric Chemistry and Physics” (John Wiley & Sons, 1998)

Photochemical Cycle of NO2, NO and O3

  • NO2 + hν (λ< 424 nm)  NO + O (jNO2)

  • O + O2 + M  O3 + M (k1)

  • O3 + NO  NO2 + O2(k2)

  • d[NO2]/dt = k2[O3][NO] - jNO2[NO2 ]

    For O atoms, O3 (very reactive), invoke pseudo-steady-state approximation, i.e., rate of formation = equals rate of loss


Atmospheric chemistry

  • d[O3]dt = k1[O][O2][M] - k2[O3][NO] ~ 0

  • d[O]/dt = jNO2 [NO2 ] – k1[O][O2][M] ~ 0

    jNO2[NO2] = k1[O][O2][M]

  • d[O3]dt = jNO2 [NO2] - k2[O3][NO] ~ 0

    Photostationary state relationship

    [O3]ss = jNO2[NO2] /k2[NO]


Atmospheric chemistry of carbon monoxide and no x

Atmospheric Chemistry of Carbon Monoxide and NOx

  • O3 + hν  O + O2

  •  O(1D) + O2

  • O(1D) + M  O + M

  • O + O2 + M  O3

  • O(1D) + H2O  2 OH

  • CO + OH CO2 + H

  • H + O2 + M HO2 + M

  • CO + OH + O2 CO2 + HO2

  • HO2 + NO  NO2 + OH


Atmospheric catalytic oxidation of co

Atmospheric Catalytic Oxidation of CO

CO + OH + O2 CO2 + HO2

HO2 + NO  NO2 + OH

NO2 + hν  NO + O

O + O2 + M  O3 + M

CO + 2O2 + hν  CO2 + O3

  • HO2,OH not consumed in this cycle

  • Net formation of O3: NO  NO2 is accomplished by HO2

  • The chain terminating step:

    OH + NO2 + M  HNO3 + M


The hydroxyl radical

The Hydroxyl Radical

  • Most important reactive radical species in the atmosphere.

  • Measurements, theoretical estimates -- average tropospheric [OH] =

    • Daytime (summer)5-10 x 106 molecules cm-3

    • Daytime (winter) 1- 5 x 106

    • Nighttime <2 x 105

  • Nighttime reservoir

    OH + NO + M  HONO + M

  • Early morning jump start

    HONO + hν  OH + NO


Peroxyacyl nitrates

Peroxyacyl Nitrates

  • CH3CHO + OH  CH3CO + H2O

  • CH3CO + O2 + M  CH3C(O)O2 + M

  • CH3C(O) O2 + NO  CH3C(O)O + NO2

  • CH3C(O)O  CH3 + CO2

  • CH3C(O)O2 + NO2 <==> CH3C(O)OONO2

    Peroxyacetyl nitrate (PAN)

CH3C=O

OONO2


Peroxyacyl nitrates1

Peroxyacyl Nitrates

  • Lower troposphere -- relatively unreactive

    • Lifetime determined by thermal dissociation

  • PAN: ~ 30 minutes at 298 K; 8 hours at 273 K; months in upper troposphere

  • Upper troposphere – lifetime determined by photolysis, OH

  • Mechanism for long-range transport of reactive NOx


Hydrocarbon oxidation in the atmosphere

Hydrocarbon Oxidation in the Atmosphere

CH4 + 4O2 + 2NO + OHHCHO + 2O3 + OH + 2NO2 + H2O

CH3CH3 + 2NO + OH + O2CH3CHO + 2NO2 + OH

C2H4 + OH + NO + 2O2 NO2 + 1.44 HCHO + 0.28 HOCH2CHO + OH


Urban atmosphere on a smoggy day

Urban Atmosphere on a Smoggy Day


Atmospheric chemistry

NOX/Hydrocarbon/Ozone

Relationships in the Atmosphere

Urban-Suburban

O3: 100-400 ppb

Rural

O3: 50-120 ppb

Marine

O3: 20-40 ppb

Remote

O3: 20-40 ppb


Ozone isopleths

Ozone Isopleths

  • Graphical representation of the dependence of O3 formation on initial [VOC] and [NOx]

  • Simple box model representation of the atmosphere

    • After initialization, nothing enters or leaves the box

  • Implications for Control of O3

    All VOC/NOx regimes are not equal


Atmospheric chemistry

  • Ridge line: low VOC/NOx vs. high VOC/NOx

  • Above ridge line

    Decreased [NOx]  increased [O3]

    Decreased [VOC]  decreased [O3]

  • Below ridge line:

    Decreased [NOx]  decreased [O3]

    Decreased [VOC]  no change in [O3]

VOC-limited

NOx-limited


Michigan air pollution http www deq state mi us documents deq aqd aqe ozone bumpdown westmich pdf

Michigan Air Pollutionhttp://www.deq.state.mi.us/documents/deq-aqd-aqe-ozone-bumpdown-westmich.pdf

  • Air quality in Michigan has been improving since the mid-1980’s


Visibility

Visibility


Extinction coefficient b ext

Extinction Coefficient - bext

  • Measure of atmospheric transparency

  • Measure of the fraction of light energy lost from a collimated beam of energy E in traversing a unit thickness of atmosphere

  • The extinction coefficient has dimensions of inverse length (e.g., Mm-1)


Atmospheric chemistry

  • bRayis light scattering by gas molecules known as Rayleigh scattering

    • Gas scattering is almost entirely attributable to oxygen and nitrogen molecules in the air.

    • It is unaffected by pollutant gases and is 12 x 10-6 m-1 (Mm-1) at the wavelength of 550nm at sea level. (Vr ~300 km)

  • bsp is light scattering by particles

    • Dominated by fine particles in the size range of 0.1~1.0 μm


Atmospheric chemistry

  • bag is light absorption by gases

    • NO2 is the only common atmospheric gas that significantly absorbs light

  • bap is light absorption by particles

    • Absorption arises nearly entirely from elemental carbon particles


Atmospheric chemistry

Dry

  • 0.1  2 µm diameter particles scatter the most light per unit mass.

  • Sulfates  ~ two-thirds of the visibility reduction in the Appalachian Mts.

  • In southern California, nitrates are the greatest contributor to haze, with organic carbon also very important.

Wet


Visual range koschmieder equation

Visual Range – Koschmieder Equation

  • Distant objects are perceived in terms of contrast against the background (usually the sky)

    • At increasing distances, both bright and dark objects fade and approach the horizon of the brightness

    • Apparent contrast relative to the horizon decreases


Atmospheric chemistry

  • Initial object contrast (Co) = ratio of the object brightness minus the horizon brightness divided by the horizon brightness.

  • For a homogeneous atmosphere (pollutant concentration, sky brightness), the apparent contrast decreases with increasing object-observer distance;

    C = Coexp(bextx)

    bext is the extinction coefficient

    x is the observer-object distance.


Atmospheric chemistry

  • For a large black object Co = -1; assume the contrast threshold for human perception is 0.02

    0.02 = - exp(bextVr) and Vr = 3.912/bext

  • Pristine coastal air: Vr ~ 160-200 km

  • Remote continental air: Vr ~ 80-120 km

  • Urban Plume: Vr ~ 5-20 km


Atmospheric chemistry

Smoke from multiple wildfires in Canada blanketed the eastern U.S. with a smoke plume nearly 200 miles wide, affecting air quality from New York to Washington D.C in July 2002. CREDIT: NASA/GSFC.


Atmospheric chemistry

B. A. Schichtel, et al, Atmospheric Environment 35, 5205-5210 (2001)

1981-1985 1986-1990 1991-1995

bext derived from Vr


Visibility trends in the eastern u s

Visibility Trends in the Eastern U.S.

Trends in improving visibility in the eastern U.S. correlate well with the decrease in SO2 emissions (precursor to particle sulfate in the atmosphere) in the U.S.


Atmospheric chemistry

Air Emissions Trends - Continued Progress Through 2003

http://epa.gov/airtrends/econ-emissions.html

National Air Pollutant Emissions Estimates for Major Pollutants


Atmospheric chemistry

This image shows ocean-crossing aerosols as dust from the Sahara desert is carried over the Atlantic Ocean. Dust and pollution from Asia floats toward the Pacific Northwest. CREDIT: NASA/GSFC.


Global warming

Global Warming


Definitions

Definitions

  • Weather: Look out the window

    • High short-time variability

      • High, low pressure systems; meandering jet stream

    • High spatial variability (E. Lansing vs. Detroit)

  • Climate

    • Weather averaged over large areas (sub-continental  global) and long time periods (decades  centuries)

    • Recent climate change in Michigan?


What determines climate

What Determines Climate?

  • Physics and Chemistry of the Atmosphere

    • Greenhouse gases; aerosols

    • Feedbacks

      • Water Vapor and Clouds

  • The Sun

  • Interactions between Biosphere and Atmosphere

  • Natural Climate Variability


  • Facts

    Facts

    • Since ~1800

      • Earth has warmed 0.8oC (since 1880)

      • GHG atmospheric concentrations have increased

        • CO2: 280 ppm  370 ppm

        • CH4: 0.7 ppm  1.75 ppm

        • N2O: 270 ppb  320 ppb

    • Climate is controlled by the Greenhouse Effect


    The natural greenhouse effect

    The Natural Greenhouse Effect

    Contribution to the Natural Greenhouse

    Water 90-95%

    Carbon Dioxide 5-7%

    Methane <1%

    Nitrous Oxide <1%


    Physics and chemistry of the atmosphere

    Physics and Chemistry of the Atmosphere

    • Greenhouse gas concentrations

      • Radiative forcings

    • Feedbacks

      • Chemistry, physics, meteorology

      • Water vapor and clouds


    Atmospheric co 2 concentrations

    Atmospheric CO2 Concentrations

    Currently ~372 ppm


    Aerosols particles

    Aerosols/Particles

    • Major impact on climate

    • Atmospherically inhomogeneous, short lifetimes – unlike GHGs

    • Direct Effects – Fairly straight-forward

      • Particles scatter and absorb solar radiation

        • Light scattering cools (all particles)

        • Light absorption warms (primarily BC and iron-containing dust)

    • Indirect Effects – Very difficult to quantify

      • Cloud formation (condensation nuclei)

      • Cloud properties (water droplet size; cloud water content)


    Feedbacks

    Feedbacks

    • 2x CO2 Direct warming ~0.5-1.0oC

    • Predictions  ~5oC require positive climate system FEEDBACKS that amplify the direct warming from the extra GHGs.

      • Water vapor

      • Clouds

    • Inherent uncertainties in feedback mechanisms


    Water vapor and clouds

    Water Vapor and Clouds

    8-Day Atmospheric Water Cycle

    • On average, clouds cover 40-45% of the Earth’s surface

    • Additional 2-3% cloud cover offsets warming from man-made GHG (+2.5 Wm-2)

    • Model grid scale requirements make it impossible to directly model clouds and their climate effects


    The sun and global warming

    The Sun and Global Warming


    Atmospheric chemistry

    Correlation Between Solar Cycle and Surface TemperatureCourtesy of George Wolff (GM)

    Dashed line is length of sun’s magnetic cycle..


    Solar hypothesis

    Solar Hypothesis

    • Excellent correlation between solar activity and temperature for past 30,000 years

    • Solar activity greatest in last 8000 years

      S. Solanki, et al., Nature (28 Oct. 2004)

    • Change in directsolar forcing  ~ 10% of the observed temperature variation

    • Solar/climate theory

      • High solar activity strengthens magnetic barrier which deflects cosmic particles away from earth (known)

      • Cosmic particles enhance cloud formation (limited recent data)


    Global average radiative forcing baseline pre industrial revolution

    Global Average Radiative ForcingBaseline: Pre-Industrial Revolution

    TAR (IPCC, 2001)


    Major forcing uncertainties

    Major Forcing Uncertainties

    • Black carbon

      • Very short-lived, strong solar energy absorber

      • As important as CO2?

    • Aerosol indirect forcing

      • Aerosols impact cloud formation, cloud characteristics

      • Offset much of the GHG warming?

    • Land use changes

      • Changes planetary surface albedo

    • Solar influence

      • An important warming component?


    Natural climate variability

    Natural Climate Variability


    Natural climate variability1

    Natural Climate Variability

    • What do we “know”?

      • 140 years of “real” data, paleo-data, GCM predictions: +0.2-0.3oC

    • 100 Years of Consensus

      • Example: Sargasso Sea Temperatures

    Medieval Warm Epoch

    Little Ice Age


    Natural climate variability2

    Natural Climate Variability

    • “Consensus” challenged in 1998 (IPCC 2001) by the Hockeystick

    • Minimized the importance of Medieval Warm Epoch; Little Ice Age – regional rather than global event


    Regional climate cycles

    Regional Climate Cycles


    El nino

    El Nino

    Australian Bureau of Meteorology


    Atmospheric chemistry

    • El Nino – hot and dry on west coast of Americas

    • La Nina – cold and rainy on west coast of Americas; intense drought in Australia

    • Global connections


    Existing issues

    Existing Issues

    • Radiative forcing – clouds, aerosols

    • Natural climate variability

      • CycleswithinCycleswithinCycles …

    • Ocean response - “Instantaneous” climate shifts freezing in the greenhouse?

    • Sea level – ice melt, thermal expansion; will the glaciers grow?

    • Carbon cycle - terrestrial sinks; deforestation

    • Land use

    • Extreme weather – floods, droughts, hurricanes

    • Regional climate change - “winners and losers”


    Global average surface temperatures

    Global Average SurfaceTemperatures


    25 year temperature trends http www junkscience com msu temps cd trends gif

    25-Year Temperature Trendshttp://www.junkscience.com/MSU_Temps/CD-Trends.GIF


    Atmospheric chemistry

    Arctic Temperature TrendsGraph from JunkScience.com


    Arctic paleoclimate overpeck et al science 278 1251 1997

    Arctic PaleoclimateOverpeck, et al., Science 278, 1251 (1997)

    Summer-weighted, Arctic-wide (29 sites)

    Annual Temperatures: Proxy Data

    T = -0.942 + 0.00313(Year-1600)

    For 1600-1800

    ~0.016 deg./yr for

    1880-1950


    Commentary on the basis of the facts

    CommentaryOn the Basis of the Facts:

    • Anthropogenic impacts on climate are occurring

    • We cannot accurately quantify those impacts

    • Prediction of future climate is very difficult

      • Significant issues involving the representation of climate science, including feedbacks, in global climate models

      • Unverifiable assumptions about societal actions and technological evolution

        • Linear extrapolations from non-linear systems


    Kyoto protocol requirements 2008 2012 timeframe vs 1990 co 2 emissions

    Kyoto Protocol Requirements2008-2012 Timeframe (vs. 1990 CO2 Emissions)

    • EU

      • Goal: -8%

      • Chance of success: uncertain, even with major emissions cuts associated with UK conversion to natural gas and the shutdown of East German industry after 1990

      • Population trends (UN, 1998): -3% (2010); -5% (2020)

    • US

      • Goal: -7%

      • Current status: +32% projected for 2010

      • Population trends: +14% (2010); +21% (2020)

    • Developing Countries (China, India, Indonesia, S. Korea) -- NO REQUIREMENTS


    Atmospheric chemistry

    Rest of World

    Other OECD

    Former Soviet Bloc

    United States

    20

    18

    16

    14

    12

    10

    8

    6

    4

    2

    0

    1990

    1992

    2000

    2005

    2010

    2025

    2100

    Growth In Developed/ Developing NationsBillion Metric Tons C/yr

    (IPCC Scenario IS92a)

    Accumulated CO2 emissions 1990 to 2100 is

    1,500 bmt C.


    Results of the kyoto protocol

    Results of the Kyoto Protocol

    • 2020 vs 1990

      • US, OECD CO2 emissions: 3 GT  to 2.8 Gt

      • RoW CO2 emissions: 1.8 Gt  to 3.0 Gt

      • Net Effect: Global CO2 emissions increase from 6 to 8 Gt (vs. 8.2 Gt) -- no measurable progress

    • 2100 vs 1990

      • US, OECD CO2 emissions  0 Gt

      • RoW - emissions increase from about 1.8 to 13.2 Gt

      • Net Effect: Global emissions increase from 6 to 15.5 Gt (vs. 20 Gt)

        • CO2 emissions are 2.5 times 1990 levels

        • Temperature rises about 1.8oC vs. 2.1oC for “no reductions”T.M.L. Wigley, Geophys. Res. Lett., 25, 2285 (1998)


    Stabilization of atmospheric co 2

    Stabilization of Atmospheric CO2

    T. Wigley, R. Richels, and J. Edmonds, Nature 379, 240 (1996)


    Stabilization of atmospheric co 2 levels

    Stabilization of Atmospheric CO2 Levels

    • Massive controls on CO2 emissions are needed for stabilization as far as 300 yearsinto the future.

      • Stabilization at 550 ppm  emissions reduced ~70% from current levels

      • Stabilization at 350 ppm  85-90% reduction in emissions (with a period of zero CO2 emissions around the year 2100).

      • The specifics of the short-term (25-50 years) emissions control scenarios have very little impact on long-term stabilization.

    • It is certain that society is on a path that will lead us to atmospheric CO2 concentrations of at least 550 ppm.


    Regional climate cycles1

    Regional Climate Cycles

    • NAO: Dominates winter climate variability in the N. Atlantic region from central North America to Europe and into Northern Asia.

      • Positive Phase: N. Atlantic intense winter storms; warm, wetwinters in Europe, eastern US

    • AO: Controlled by sea level pressure in the Arctic

      • “High index” or “warm phase”: Below normal Arctic SLP, enhanced upper level westerlies in the N. Atlantic; warm US winters; warm, wet winters in N. Europe; thinning Arctic sea ice.

    • PDO: Long-term ocean fluctuation of the Pacific Ocean

      • Major impacts in the N. Pacific, especially along N. America

      • Positive (warm) phase: SSTs cool in central, north Pacific, warm along N. America coast


    Atmospheric chemistry

    • NAO: Controlled by Icelandic low pressure vs. subtropical high pressure

      • Dominates winter climate variability in the N. Atlantic region central North America to Europe and into Northern Asia.

      • Positive Phase: N. Atlantic intense winter storms; warm, wet winters in Europe, eastern US

      • Negative Phase: Fewer N. Atlantic storms; cold winters (snow) in Europe, eastern US.

        http://www.ldeo.columbia.edu/NAO/

    • AO: Controlled by sea level pressure in the Arctic

      • “High index” or “warm phase”: Below normal Arctic SLP, enhanced upper level westerlies in the N. Atlantic; warm US winters; warm, wet winters in N. Europe; thinning Arctic sea ice.

      • “Low index” or “cool phase”: Above normal Arctic SLP, weak upper level westerlies; cold US, N. Europe winters; robust Arctic sea ice.

        http://jisao.washington.edu/wallace/natgeo/ArcticSubart.pdf

    • PDO: Long-term ocean fluctuation of the Pacific Ocean

      • Major impacts in the N. Pacific, especially along N. America

      • Negative (cool) phase: SSTs warm in central, north Pacific, cool along N. America coast

      • Positive (warm) phase: SSTs cool in central, north Pacific, warm along N. America coast

        http://sealevel.jpl.nasa.gov/science/pdo.html


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