Modeling of trace gases from the 1998 North Central Mexico forest fire smoke plume, as measured over Phoenix

Abstract. Forest fires in North and Central America have been frequent and extensive over the past few years. Though much research has addressed the effects of forest fires in tropical South America and Africa on regional and global-scale oxidants, the same is not true for North America. Here we show that one of the days during an intensive field campaign conducted over Phoenix, Arizona, in 1998 was substantially influenced by transport from forest fires in central and southern Mexico. We combined data collected from aircraft platforms, surface stations, and satellite with model results to establish that the origin of the air sampled over Phoenix on 20 May 1998, was from forest fires in Mexico. We also investigated the effect of the smoke layer on photolysis rates and hence photochemistry over a five-day travel period from the source region to Phoenix. The results show that a smoke layer could reduce photolysis rates of key tropospheric constituents significantly and decrease the oxidant formation rates during the first few days of the plume history. The ultimate effect of the smoke layer on the evolution of oxidants in the plume was, however, shown to be minimal.