21. Measurements of PM2.5 Carbon in New York City

James J. Schwab and Kenneth L. Demerjian
Atmospheric Science Research Center, University of Albany, State University of New York, 251 Fuller Road, Albany, NY 12203

Semi-continuous measurements of PM2.5 carbon have been made since July 2002 at Queens College using a Rupprecht and Patashnick, Series 5400 Ambient Carbon Particulate Monitor, and since May 2003 in the South Bronx using a Magee Scientific, Aethalometer. At the Queens College site the R&P 5400 reports hourly measurements of carbon at 340 C (volatile “organic” carbon fraction) and 750 C (total carbon). The difference between the 750 and 340C burn measures the stable (elemental) carbon fraction. Total collected carbon concentrations ranged from 2 to 5 mg/m3 with elemental carbon from 0.5 to 2.0 mg/m3. Concentrations were approximately 30-40% higher in summer compared to winter. Elemental carbon showed a peak from 6 to 10 am coinciding with the peak in traffic volume whereas total carbon showed a broader peak extending from noon to 4 pm.
At the south Bronx site the aethalometer records five-minute average measurements of black carbon. The black carbon concentrations at the South Bronx show a clear diurnal trend with peak concentrations from 8 am to noon. This diurnal trend tracks NOx and nitrate concentrations and is similar to the elemental carbon trend at the Queens College site, which is consistent with mobile and combustion emission sources.
At both sites a collocated R&P 2300 speciation sampler provides 24-hour PM2.5 carbon measurements on a quartz filter every 3rd day. In addition a series of collocated instruments provide hourly measurements of various pollutant gases. Data from the semi-continuous carbon instruments will be presented and compared to other collocated instruments.