VERTICAL PROFILES AND HORIZONTAL TRANSPORT OF ATMOSPHERIC AEROSOLS AND TRACE GASES OVER CENTRAL ONTARIO

The Canadian intensive measurement periods of the Eulerian Model Evalu ation Field Study (EMEFS) were conducted in the summer of 1988 and the spring of 1990 in central Ontario, Canada. The project involved using instrumented research aircraft to measure vertical profiles of atmosp heric aerosols and trace gases over special ground observing sites. Ox idant concentrations were often highest aloft, There were no strong di urnal variations in O-3 and H2O2, suggesting that oxidant concentratio ns reported in this paper, as well as other species, seem to be most i nfluenced by transport mechanisms rather than local chemical transform ations. Aerosol and SO, concentration vertical profiles tended to be s imilar to those of water vapor mixing ratio, showing a maximum near th e surface, which points to a ground level source for these constituent s. The inorganic aerosol was dominated by sulphate during the summer m easurements, but particulate nitrate was important during the spring. The horizontal transport of these species was calculated for air with back trajectories from the north or south, showing transport to occur primarily from west to east for both cases, with components to the sou th or north, respectively. The sulphur is transported primarily as SO, in the spring and about half as SO2 and half as SO4= in the summer. A ir from the south is a source of particles, S, H2O, O-3, H2O2 and NO2 to this region. Similarly, cloud water concentrations of sulphate and nitrate were higher with southerly trajectories, as were aircraft filt er measurements of sulphate, nitrate, ammonium, and nitric acid.