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We analyzed observations from the Multi-angle Imaging SpectroRadiometer(MISR) to determine the injection heights of biomass-burning smoke plumesover peninsular Southeast Asia (PSEA, here defined as Vietnam, Cambodia, Thailand, Laos, and Myanmar) in the spring, with the goal ofevaluating the impacts on long-range pollutant transport. We retrieved theheights of 22 000 MISR smoke pixels from 607 smoke plumes overPSEA during February to April of the years 2001–2010. Forty-five percentof the analyzed smoke pixels were above the local mean boundary layer (1 km)at MISR overpass time (10:30 a.m. local time). We used the GEOS–Chem model tosimulate the transport of PSEA biomass-burning pollutants in March 2001. Ona monthly mean basis, we found that the direct injection of 40% of thePSEA biomass-burning emissions had little impact on the long-range transportof CO to downwind regions, compared to a control simulation where allbiomass-burning emissions were released in the boundary layer. This wasbecause CO at the surface over PSEA was efficiently lifted into the freetroposphere by deep convection associated with synoptic-scale weathersystems. For pollutants with lifetimes shorter than the synoptic timescale,such as black carbon aerosol (BC), their long-range transport was much moresensitive to the initial plume injection height. The direct injection ofNO<sub>x</sub> from PSEA biomass burning into the free troposphere drove increasedformation and transport of peroxyacetyl nitrate (PAN), which in turn led to a small increase inozone over downwind southern China and the northwestern Pacific. The Pacificsubtropical high transported BC emitted from PSEA biomass burning to themarine boundary layer over the tropical northwestern Pacific. We comparedour model results to aircraft measurements over the northwestern Pacificduring the TRACE-P campaign (March 2001). The direct injection of 40% ofthe PSEA biomass-burning pollutants into the free troposphere in the model ledto a more pronounced BC peak at 3 km over the northwestern Pacific. Ouranalysis highlights the point that the injection heights of smoke plumespresents great uncertainty over the interpretation of BC measurements downwind ofbiomass-burning regions

Injection heights of springtime biomass-burning plumes over peninsular Southeast Asia and their impacts on long-range pollutant transport