Source Identification of Houston Aerosol with Carbon Fractions in Positive Matrix Factorization / Paul Chiou...et.al.

Speciated samples of PM,, were collected at the Deer Park site in Houston, Texas by US EPA (Environmental Protection Agency) from July of 2004 to December of 2007. A total of 307 (Envirorwich 55 species including 4 organic carbon fractions were measured however were excluded because of too many below-detection-limit data. The data set was analyzed by positive matrix factorization (PMF) to infer the sources of PM observed at the site. The analysis identified ten source-related factors: sulfate-rich secondary aerosol (53.3%), highway traffic (13.7%), aged sea-salt (7.5%), airborne soil (5.4%), nitrate-rich secondary aerosol (5.3%) gasoline vehicle (5.3%), wood smoke (3.4%), railroad traffic (3.1%), sea salt (1.7%), and on- road diesel emissions (1.2%). Sulfate and nitrate mainly exist as ammonium salts. The sulfate- rich secondary aerosol accounts for the highest of the PM, mass concentration at the site. The factor containing highest concentrations of Cl and Na was attributed to sea salt due to the proximity of the monitoring sites to the Gulf of Mexico. The aged sea-salt was related to the sea salt aerosol but was separately identified because of the chlorine replacement reactions. Furthermore, unlike some previous studies (Chiou et al. 2008, 2009) using only the traditional OC data, this study demonstrates that the utilization of fractional carbon data can enhance source apportionment to separate diesel emissions from gasoline vehicle sources.