Hourly Measurements of Fine Particulate Sulfate and Carbon Aerosols at the Harvard–U.S. Environmental Protection Agency Supersite in Boston

Abstract

Hourly concentrations of ambient fine particle sulfate and carbonaceous aerosols (elemental carbon [EC], organic carbon [OC], and black carbon [BC]) were measured at the Harvard–U.S. Environmental Protection Agency Supersite in Boston, MA, between January 2007 and October 2008. These hourly concentrations were compared with those made using integrated filter-based measurements over 6-day or 24-hr periods. For sulfate, the two measurement methods showed good agreement. Semicontinuous measurements of EC and OC also agreed (but not as well as for sulfate) with those obtained using 24-hr integrated filter-based and optical BC reference methods. During the study period, 24-hr PM_2.5 (particulate matter [PM] ≤ 2.5 µm in aerodynamic diameter) concentrations ranged from 1.4 to 37.6 µg/m³, with an average of 9.3 µg/m³. Sulfate as the equivalent of ammonium sulfate accounted for 39.1% of the PM_2.5 mass, whereas EC and OC accounted for 4.2 and 35.2%, respectively. Hourly sulfate concentrations showed no distinct diurnal pattern, whereas hourly EC and BC concentrations peaked during the morning rush hour between 7:00 and 9:00 a.m. OC concentrations also exhibited nonpronounced, small peaks during the day, most likely related to traffic, secondary organic aerosol, and local sources, respectively.