**Report of IAMAS Session A8. The Intercontinental Transport of
Pollution**

By W.R. Stockwell and A.M. Thompson

Many important papers and abstracts were presented in the IAMAS session
A8, the Intercontinental Transport of Pollution. New measurement and
modeling studies show that trace gases and particulate matter are
transported over intercontinental distances. An extensive dataset has
been collected by A.M. Thompson et al. The dataset is based over 2700
in-situ ozone soundings in the southern hemisphere, the Southern
Hemisphere Additional Ozonesondes network (SHADOZ). One of the most
interesting findings of the SHADOZ analysis is that Indian Ocean
regional pollution may contribute up to half of the \'\'excess\'\' ozone
observed in the south tropical Atlantic \'\'paradox\'\' in the
December-January-February period of the year. Thompson and colleagues
also performed ozonesonde launches during the International Consortium
on Atmospheric Research on Transport and Transformation/Intercontinental
Transport Experiment/New England Air Quality Study (ICARTT/INTEX/NEAQS).
They found that the American west coast showed influences of long-range
pollution transport from Asia and that there are frequent impacts of
stratospheric ozone in the free troposphere.

T. Zhao et al. used satellite based, remotely sensed data, aircraft and
surface site observations to examine the trans-Pacific transport of
Asian aerosols from Asia to North America and the Global Environment
Multiscale - Air Quality model) and found that all natural aerosol
components show strong seasonal variations and interannual variability.
They found that monthly averaged Asian dust outflow from the East Asian
subcontinent showed peak transport from 38°N in March; 42°N in April and
47°N in May, respectively. Carbonaceous aerosol from bio-mass burning in
East Siberia has a major impact on the surface PM values in North
America during summer peak fire season. B. Wang et al. found that the
impact of Asian anthropogenic emissions on North America appeared to be
persistent throughout the entire year with monthly variations. Their
simulations showed that although the maximum monthly average of PM2.5 in
Asia the maximum impact of Asian anthropogenic emissions on North
America appeared in Spring (April and May), while the minimum in Summer
(July and August) due to variations in the emissions and meteorological
transport conditions.

J. Nielsen-Gammon and J. Tobin found that background ozone has an annual
double-peaked structure, with highest values in April-May and in
August-September. The intraseasonal variability is greatest for
locations not strongly affected by the transport of pollution from North
American. The background could be higher in the spring by 10 to 15 ppbv
regardless of the transport wind pattern.

New measurement programs include the development of the Regional
Atmospheric Measurement Modeling and Prediction Program (RAMMPP) by B.
Taubman et al. RAMMPP was developed to conduct integrated, long-term air
quality studies in the region and analyzing trans-boundary pollution
transport processes. This program includes ground-based and airborne
measurements; meso-scale meteorological modeling, air quality modeling
and air quality forecasting.

Many papers involving the application of meteorological and air quality
models were presented. O. Wild et al. found that tropospheric ozone and
ozone precursor concentrations chemical over central and eastern Asia
are influenced by the emission of pollutants and ozone precursors over
the heavily populated and industrialized regions of Europe. K. Sudo et
al. performed simulations that showed O~3~ transport from the polluted
source regions accounts for more than 40% of net ozone even in remote
locations and O~3~ export from boundary layers in China and free
troposphere in eastern Asia affects much of the NH, and even the
southern hemisphere.

M. Chin et al. reported on the intercontinental transport of aerosols
and its implications for regional air quality. The model, Goddard
Chemistry Aerosol Radiation and Transport (GOCART) model was used to
simulate the effect of long-range transport on regional aerosol
concentrations. G. Luo and Z. Wang developed a new global environmental
atmospheric transport model (GEATM) to investigate the distribution,
transport and deposition patterns of sulfate, black carbon (BC) and dust
aerosol. The simulation results of GEATM were compared with several
observational datasets over the world and the correlation coefficient
was greater than 0.6. Y. Wang (Georgia Institute of Technology, United
States) used a global chemical transport model ti simulate observations
from the Tropospheric Ozone Production about the Spring Equinox (TOPSE)
experiment. H Guan et al. modeled the impact of African and South
American savanna fires on global atmospheric carbon monoxide levels
using the National Center for Atmospheric Research Community Atmospheric
Model. The burning is most intense during September, October, and
November and they found that carbon monoxide plumes cover the entire
tropical belt between the west coast of South America and the east coast
of Africa and beyond due to tropospheric air transported from Brazil
over the Atlantic by high level westerly winds, and from Africa by
easterlies in the lower and middle troposphere. Guerova et al. used the
GEOS-CHEM) simulations O~3~ and CO observations with ground based
instruments, ozone profiles from MOZAIC and total tropospheric CO and
NO~2~ column observations from the MOPITT and GOME instruments to
identify a number of major North American plumes in summer 2000 and
2003.

The linkage between the global, regional and urban scales is receiving
greater recognition of its importance. W.R. Stockwell and D. Kim used a
version of the MM5 meteorological model with inline coupled atmospheric
chemistry to simulate the flow of polluted air over the Sierra-Nevada
Mountains. They found that plumes and isolated parcels of air pollutants
were transported to upper troposphere, as high as 5 km. Because high
mountains occupy a large fraction of the Earth\'\'s surface their
effects on air pollutants may contribute strongly to their global air
pollution and climate change. Long-range transport may affect the urban
scale and the session included presentations concerning this scale (A.
Deniz; H. Toros). Y.S. Ghim investigated the effect of long-range
transport and secondary formation on particulate matter concentrations
in Asia. The urban scale could be considered to be the most important
because this is where pollution will lead to the greatest health
effects. The greatest human health effects will occur in developing
countries with the highest population growth. Emission increases due to
the developing energy sector may also be the highest in these countries
(E.O. Archibong).

New research was presented on the long-range transport of pollutants
that have traditionally been considered as urban air pollutants
including metals and Persistent organic pollutants (POPs). A. Baklanov
et al. investigated the long-range atmospheric transport and deposition
of copper, nickel and sulfate emissions from the Russian Arctic with the
Danish Emergency Response Model of Atmosphere (DERMA) of the DMI in the
long-term mode. X. Zhang et al. examined the composition by XPS of
particles collected during quiet periods and during dust storms over
Beijing and Inner Mongolia. They found that both S and Fe were enriched
on the surface of dust storm aerosol particles and hypnotized that there
could be some coupling between the iron and sulfur in aerosols during
the long-range transport. Persistent organic pollutants (POPs) are very
unreactive compounds that include polychlorinated biphenyls (PCBs). Ghim
et al. measured POPs through collection with polyurethane foam and
quartz fiber filter, respectively, on a high volume sampler. S. Gong and
P Huang used the Global Environmental Multiscale - Air Quality model)
with active aerosols to simulate the transport and partitioning between
gaseous and aerosol phases. The found that POPs can be readily
transported long distances on the prevailing air currents and may remain
in the atmosphere as long as 3 months.