NASA Scientific and Technical Aerospace Reports

pollution influence exceeds European influence in the UT-MT, reflecting the uplift from convection and the warm conveyor
belts over the eastern seaboard of North America. African outflow makes a major contribution to ozone in the low-latitude
MT-UT over the Pacific Rim during November- April. Lightning influence over the Pacific Rim is minimum in summer due
to westward UT transport at low latitudes associated with the Tibetan anticyclone. The Asian outflow flux of ozone to the
Pacific is maximum in spring and fall and includes a major contribution from Asian anthropogenic sources year-round.
Author
Troposphere; Ozone; Pollution Transport; Three Dimensional Models; Biomass Burning; Atmospheric Composition
20040111415 Harvard Univ., Cambridge, MA, USA
Analysis of 1970-1995 Trends in Tropospheric Ozone at Northern Hemisphere Midlatitudes with the GEOS-CHEM
Model
Fusco, Andrew C.; Logan, Jennifer A.; Journal of Geophysical Research; January 2004; ISSN 0148-0227; Volume 108, No.
D15, pp. 4-1 - 4-25; In English; Original contains black and white illustrations
Contract(s)/Grant(s): NAG1-2307; NSF ATM-99-03529; Copyright; Avail: Other Sources
I ] The causes of trends in tropospheric ozone at Northern Hemisphere midlatitudes from 1970 to 1995 are investigated
with the GEOS-CHEM model, a global three-dimensional model of the troposphere driven by assimilated meteorological
observations from the Goddard Earth Observing System (GEOS). This model is used to investigate the sensitivity of
tropospheric ozone with respect to (1) changes in the anthropogenic emission of nitrogen oxides and nonmethane
hydrocarbons, (2) increases in methane concentrations, (3) variations in the stratospheric source of ozone, (4) changes in solar
radiation resulting from stratospheric ozone depletion, and (5)increases in tropospheric temperatures. Model results indicate
that local increases in NO, emissions have caused most of the increases seen in lower tropospheric ozone over Europe and
Japan. Increases in methane are responsible for roughly one fifth of the anthropogenically induced increase in tropospheric
ozone at northern midlatitudes. However, changes in ozone precursors do not adequately explain either the spatial differences
in observed ozone trends across midlatitudes or the observed decreases in ozone over Canada throughout the troposphere. We
argue that ozone depletion in the lowermost stratosphere is likely to have reduced the stratospheric source by as much as 30%
from the early 1970s to the mid 1990s. Model simulations that account for such a reduction along with reported changes in
anthropogenic emissions show steep declines of ozone in the upper troposphere and variable increases in the lower troposphere
that are more consistent with observations. Differential temperature trends in summer between North America and Europe may
account for at least some of the remaining spatial variation in tropospheric ozone trends. Increases in ultraviolet (UV) radiation
due to stratospheric ozone depletion do not appear to significantly reduce tropospheric ozone, except at midlatitudes in the
Southern Hemisphere following the breakup of the ozone hole.
Author
Troposphere; Ozone Depletion; Three Dimensional Models; Atmospheric Composition; Atmospheric Temperature;
Meteorological Parameters
20040111417 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Global and Regional Decreases in Tropospheric Oxidants from Photochemical Effects of Aerosols
Martin, Randall V.; Jacob, Daniel J.; Yantosca, Robert M.; Chin, Mian; Ginoux, Paul; Journal of Geophysical Research; 2003;
ISSN 0148-0227; Volume 108, No. D3, pp. 6-1 - 6-14; In English; Original contains color and black and white illustrations
Contract(s)/Grant(s): NAG1-2307; Copyright; Avail: CASI; A03, Hardcopy
We evaluate the sensitivity of tropospheric OH, O3, and O3 precursors to photochemical effects of aerosols not usually
included in global models: (1) aerosol scattering and absorption of ultraviolet radiation and (2) reactive uptake of HO’, NO2,
and NO3. Our approach is to couple a global 3-D model of tropospheric chemistry (GEOS- CHEM) with aerosol fields from
a global 3-D aerosol model (GOCART). Reactive uptake by aerosols is computed using reaction probabilities from a recent
review (gamma(sub HO2) = 0.2, gamma(sub NO2) = 10(exp -4), gamma(sub NO3) = l0(exp -3). Aerosols decrease the O3
- O((sup 1)D) photolysis frequency by 5-20% at the surface throughout the Northern Hemisphere (largely due to mineral dust)
and by a factor of 2 in biomass burning regions (largely due to black carbon). Aerosol uptake of HO2 accounts for 10-40%
of total HOx radical ((triple bonds)OH + peroxy) loss in the boundary layer over polluted continental regions (largely due to
sulfate and organic carbon) and for more than 70% over tropical biomass burning regions (largely due to organic carbon).
Uptake of NO2 and NO3 accounts for 10-20% of total HNO3 production over biomass burning regions and less elsewhere.
Annual mean OH concentrations decrease by 9% globally and by 5-35% in the boundary layer over the Northern Hemisphere.
Simulated CO increases by 5- 15 ppbv in the remote Northern Hemisphere, improving agreement with observations. Simulated
boundary layer O3 decreases by 15- 45 ppbv over India during the biomass burning season in March and by 5-9 ppbv over
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