[1] Smoke and pollutants from Canadian forest fires are sometimes transported over the United States at low altitudes behind advancing cold fronts. An unusual event occurred in July 2002 in which smoke from fires in Quebec was observed by satellite, lidar, and aircraft to arrive over the Washington, D.C., area at high altitudes. This elevated smoke plume subsequently mixed to the surface as it was entrained into the turbulent planetary boundary layer and had adverse effects on the surface air quality over the region. Trajectory and three-dimensional model calculations confirmed the origin of the smoke, its transport at high altitudes, and the mechanism for bringing the pollutants to the surface. Additionally, the modeled smoke optical properties agreed well with aircraft and remote sensing observations provided the smoke particles were allowed to age by coagulation in the model. These results have important implications for the long-range transport of pollutants and their subsequent entrainment to the surface, as well as the evolving optical properties of smoke from boreal forest fires.

[1] In situ measurements of trace gases and aerosol optical properties were made in March 2005 at Xianghe (39.798°N, 116.958°E, 35 m), a rural site about 70 km southeast, and generally downwind of the Beijing metropolitan area. High pollutant levels were observed during the experiment, with CO (1.09 ± 1.02 ppmv, average ± standard deviation), SO 2 (17.8 ± 15.7 ppbv), NO y (26.0 ± 24.0 ppbv), aerosol scattering coefficients (b sp , (468 ± 472) Â 10 À6 m À1 ), and aerosol absorption coefficients (b ap , (65 ± 75) Â 10 À6 m À1 ) all much higher than observed at some rural sites in the United States. O 3 (29.1 ± 16.5 ppbv) was relatively low during this study, suggesting inactive photochemical processes. Strong synoptic fluctuations in pollutant levels were detected every 4-5 days during the experiment, as cold fronts passing over the region drastically reduced the ground-level pollution. Very little precipitation was measured during the whole observational period, implying pollutant uplift and transport by rain-free cold fronts and dry convection. The observed CO/NO y ratio agrees better with inventories. Further analysis suggests that such comparisons may shed some light on the quality of emission inventories, but quantification of any error requires more extensive measurements over longer period and larger areas, as well as direct characterization of emission sources, especially mobile sources and small boilers. Using black carbon (BC)/CO ratio from the experiment, BC emissions from China are estimated at about 1300 Gg (10 9 g)/yr, but could be as high as 2600 Gg/yr.

[1] The meteorological mechanisms for lofting trace gases and aerosols out of the planetary boundary layer (PBL) into the free troposphere are key to understanding local air pollution problems as well as regional and global atmospheric chemistry and climate issues. Over the North American continent, convective storms and lifting in warm conveyor belts transport pollutants into the free troposphere. Little is known about the vertical distribution of pollutants and dust over east Asia, and the processes leading to transport, transformation, and removal of these species remain uncertain. To provide insight into these mechanisms, we report on eight flights based out of Shenyang in NE China as part of the U.S./China EAST-AIRE project conducted in April 2005. We evaluate profiles of trace species, along with back trajectories and satellite data, in the meteorological context of cyclonic systems. The warm-sector PBL air ahead of a cold front was highly polluted, while in the free troposphere concentrations of trace gases and aerosols were lower, but well above background; we measured $300 ppb CO, $2 ppb SO 2 , $70 ppb O 3 , and $ 8 Â 10 À5 m À1 aerosol scattering between $1000 and 4000 m altitude. Satellite observations indicate that the entire plume contained almost 10 5 tons of SO 2 and that the gas decayed with a lifetime of 3-5 d. Roughly the same mass of aerosol was transported into the free troposphere. Over the east Asian continent, dry convection appears to dominate with warm conveyor belts first coming into play as the cyclonic systems move off the coast.

[1] From 1997 to 2003, airborne measurements of O 3 , CO, SO 2 , and aerosol properties were made during summertime air pollution episodes over the mid-Atlantic United States (34.7-44.6°N, 68.4-81.6°W) as part of the Regional Atmospheric Measurement, Modeling, and Prediction Program (RAMMPP). Little diurnal variation was identified in the CO, SO 2 , and Å ngström exponent profiles, although the Å ngström exponent profiles decreased with altitude. Boundary layer O 3 was greater in the afternoon, while lower free tropospheric O 3 was invariant at $55 ppbv. The single scattering albedo increased from morning to afternoon (0.93 ± 0.01À0.94 ± 0.01); however, both profiles decreased with altitude. A cluster analysis of back trajectories in conjunction with the vertical profile data was used to identify source regions and characteristic transport patterns during summertime pollution episodes. When the greatest trajectory density lay over the northern Ohio River Valley, the result was large O 3 values, large SO 2 /CO ratios, highly scattering particles, and large aerosol optical depths. Maximum trajectory density over the southern Ohio River Valley resulted in little pollution. The greatest afternoon O 3 values occurred during periods of stagnation. North-northwesterly and northerly flow brought the least pollution overall. The contribution of regional transport to afternoon boundary layer O 3 was quantified. When the greatest cluster trajectory density lay over the Ohio River Valley ($59% of the profiles), transport accounted for 69-82% of the afternoon boundary layer O 3 . Under stagnant conditions ($27% of the profiles), transport only accounted for 58% of the afternoon boundary layer O 3 . The results from this study provide a description of regional chemical and transport processes that will be valuable to investigators from the Baltimore, New York, and Pittsburgh EPA Supersites.

Abstract. The relative importance of biomass-burning (pyrogenic) emissions from savannas, deforestation, agricultural waste burning, and biofuel consumption to tropospheric ozone abundance over Africa has been estimated for the year 1993, on the basis of global model calculations. We also calculated the importance of this emission source to tropospheric ozone in other regions of the world and compared it to different sources on the African regional and global scales. The estimated annual average total tropospheric ozone abundance over Africa for the reference year is 26 Tg. Pyrogenic, industrial, biogenic, and lightning emissions account for 16, 19, 12, and 27%, respectively, while stratospheric ozone input accounts for 26%. In the planetary boundary layer over Africa, the contribution by biomass burning is -24%. A large fraction of the African biomass-burning-related ozone is transported away from the continent. On a global scale, biomass burning contributes -9% to tropospheric ozone. Our model calculations suggest that Africa is the single most important region for biomass-burning-related tropospheric ozone, accounting for -35% of the global annual pyrogenic ozone enhancement of 29 Tg in 1993. IntroductionLarge-scale air pollution has traditionally been associated with anthropogenic activities in the industrialized rcgions of the world, primarily in the Northern Hemisphere. }-towever, satellite measurements of tropospheric ozone (03) have shown that in addition to distinct plumes emanating from North America, Asia, and Europe, a large amount of O3 pollution originates from tropical Africa [Fishman and Larsen, 1987;Fishman et al., 1986Fishman et al., , 1990 •Presently at University of the Witwatersrand, Johannesburg, South In this paper we report on the use of a gridded biofuelrelated trace gas emission inventory created from our studies in Africa, as partial input to a three dimensional (3-D) numerical model of atmospheric transport and chemistry (Tracer Model version 3 (TM3)). The aim is to quantitatively examine the relative influence of pyrogenic emissions on tropospheric photochemistry in Africa in particular, and globally in general, during the year 1993. Model DescriptionThe model used in this study is the Tracer Model version 3 (TM3), a 3-D atmospheric transport and chemistry model which is an updated version of TM2 described by Heimann In order to facilitate the interpretation of our model results and as a check on their numerical accuracy, we stored the tendencies by all chemical reactions, wet and dry removal processes, emissions, and transport. To reduce the output, these tendencies were stored for three vertical zones roughly representing the boundary layer, the free troposphere, and the stratosphere. Furthermore, in this study, budgets were redefined so that they are given per global region (see section 3.2.2 for the global regions used) with oceans being considered separately as a single region. For simplicity, in the budgets the troposphere is defined as the region up to 100 hPa, which in the e...