Fine and Coarse Carbonaceous Aerosol in Houston, TX, during DISCOVER-AQ

Abstract

To investigate major sources and trends of particulate pollution in Houston, total suspended particulate (TSP) and fine particulate matter (PM2.5) samples were collected and analyzed. Characterization of organic (OC) and elemental (EC) carbon combined with realtime black carbon (BC) concentration provided insight into the temporal trends of PM2.5 and coarse PM (subtraction of PM2.5 from TSP) during the Deriving Information on Surface Conditions from Column and VERtically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) Campaign in Houston in 2013. Ambient OC, EC, and BC concentrations were highest in the morning, likely due to motor vehicle exhaust emissions associated with the morning rush hour. The morning periods also had the lowest OC to EC ratios, indicative of primary combustion sources. Houston also had significant coarse EC at the downtown site, with an average (±standard deviation) PM2.5 to TSP ratio of 0.52 ± 0.18 and an average coarse EC concentration of 0.44 ± 0.24 µg·C·m−3. The coarse EC concentrations were likely associated with less efficient industrial combustion processes from industry near downtown Houston. During the last week (20–28 September, 2013), increases in OC and EC concentrations were predominantly in the fine fraction. Both PM2.5 and TSP samples from the last week were further analyzed using radiocarbon analysis. Houston’s carbonaceous aerosol was determined to be largely from contemporary sources for both size fractions; however, PM2.5 had less impact from fossil sources. There was an increasing trend in fossil carbon during a period with the highest carbonaceous aerosol concentrations (September 24 night and 25 day) that was observed in both the PM2.5 and TSP. Overall, this study provided insight into the sources and trends of both fine and coarse PM in a large urban U.S. city impacted by a combination of urban, industrial, and biogenic emissions sources.