Spatial and temporal variability of black carbon in New York City

[ 1] Measurements of black carbon ( BC) were made at two sites in New York City during the winter of 2004 and are compared. Spatial and temporal variability in the black carbon concentrations were explored by examining the diurnal, weekday/weekend, and day-of-week trends in black carbon concentrations at these two sites. It was observed that BC tracked PM2.5 well at the Queens site and contributed about 8% to the fine particle mass measured at this site. At the IS 52 site, however, BC did not track PM2.5 as well and accounted for a slightly higher 11% of the total fine mass. Diurnal BC behavior was observed during weekdays as well as weekends consistent with traffic patterns and atmospheric mixing conditions. However, a clear day-of-week dependence of BC concentrations was not observed. Conditional probability functions were computed using the surface wind data and the BC concentrations at the two sites and were used to identify local point sources. Associations of black carbon with gaseous pollutants such as CO, NOx, and nonmethane hydrocarbons are also explored for the Queens site in an attempt to identify the temporal variations in their emissions. It was found that the concentrations of black carbon vary in response to the interplay of source activity, meteorological conditions, and spatial factors. The high time resolution measurements were found to yield insights into the spatial scales of emissions that are not possible with longer timescale measurements such as 24 hour averages.