The Impact of Urban and Industrial Emissions on Mesoscale Precipitation Quality

Results from an acid rain field study around the city of Philadelphia are presented. The study involved the sampling of wet deposition at a network of 40 sites within a distance of 60 km from the Delaware River. Emphasis was placed on event-type rain sampling of frontal and primarily nonconvective storms which are responsible for most of the Northeast’s wet deposition. For most storms, meteorological conditions contributed to a predominant southeasterly transport. Since most of the area’s urban and industrial emissions occur along the Delaware River, the Pennsylvania sector of the network was identified as the downwind (target) region; the New Jersey sector was the upwind (control) region. Local emissions appear to impact the deposition of nitrate (NO₃?) which may register increases greater than 200%. It appears that this impact grows with distance from the river suggesting peaks beyond the 60 km boundary of the network. Comparisons with estimates of NO _x emissions reveal that a substantial fraction may be deposited as NO₃? on the mesoscale. The impact of local emissions on total sulfur is less striking; for some storms the sulfur excess is only in the form of dissolved SO₂. Storm-to-storm variabilities in meteorological conditions, emissions, and oxidant availabilities are probable causes of the variability in the magnitude of the local impact.