Seasonal estimation of organic mass to organic carbon in PM2.5 at rural and urban locations in New York state

Estimates of the seasonality of the ratio of fine particulate organic matter (OM) to fine particulate organic carbon (OC) are determined for data collected at the Pinnacle State Park (PSP) in rural upstate New York and at Queens College (QC) in New York City over a 3 year period from 2002 through 2004. The reconstructed mass balance method, which assigns as organic matter all of the fine particulate matter mass that cannot be attributed to sulfate ion, nitrate ion, ammonium ion, elemental carbon, water and metal oxides, is used for estimating the OM/OC ratio and assessing the seasonal variations in OM/OC ratio. The organic mass concentrations measured by an Aerosol Mass Spectrometer (AMS) for a much shorter period are compared to organic mass by the reconstructed mass balance as a check on the method. The time series of the seasonal estimates for the OM/OC ratio indicates that the 3-year-average falls between 1.5 and 1.9 at the PSP site for this period. The warm season average OM/OC ratios of 2.1 are slightly higher than cold season. The urban site OM/OC ratio does not vary systematically with season and falls between 1.3 and 1.6.