The first of two intensive summer studies of particles, ozone, and their precursors was performed between 26 June and 20 August 1999 in Philadelphia PA. Data for surface level measurements of hourly PM2.5, total sulfate, black carbon soot (BC), and particle number concentrations made by the Harvard School of Public Health are reported here. Temporal relationships between these pollutants are explored, focusing on associations of various pollutants with PM2.5. Integrated measurements of nitrate, nitric acid, and elemental and organic carbon were made on a 10 hour day/night basis starting at 8AM and 8PM EDT; this sample schedule was chosen to separate the daytime and night-time periods with very different mixing heights.

The summer of 1999 in the Philadelphia area had several intervals of elevated PM2.5 and/or ozone. The strongest associations for data from all hours was between PM2.5 and sulfate (r=0.94). On average, sulfate-related mass (sulfate x 1.37, assuming ammonium sulfate) accounted for 55% of the PM2.5; this fraction increases with PM2.5 as indicated by the somewhat non-linear relationship between sulfate and PM2.5 concentrations. For hours with PM2.5 > 60 µg/m3 (N=18), the mean of this fraction was 71%. Correlations between hourly PM2.5 and count concentration (r=0.44) or BC (r=0.31) were lower. Daily mean values were used to assess the relationship between PM2.5 and ozone (r=0.77) and for sulfate and SO2 (r=0.62).