The Impact of Urban and Industrial Emissions on Mesoscale Precipitation Quality

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Abstract
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.

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