Mass balance closure and the Federal Reference Method for PM2.5 in Pittsburgh, Pennsylvania

Abstract

Daily ambient aerosol samples were taken in Pittsburgh, Pennsylvania from the summer 2001 to the winter 2002 as part of the Pittsburgh Air Quality Study (PAQS). The study measured PM 2.5 mass by the Federal Reference Method (FRM) and the PM 2.5 chemical composition by a variety of filter-based and continuous instruments. This paper examines the mass balance between the FRM-measured mass and the sum of the aerosol chemical components. For the 7-month study period, the average FRM-measured mass is 11% greater than the sum of the mass of the aerosol chemical components. This mass balance discrepancy varies seasonally, with the average FRM-measured mass 17% greater than the sum of the chemical components for the summer months, with discrepancies as large as 30% during certain periods. Meanwhile, the FRM-measured mass was at or slightly below the sum of the chemical components for the winter months.The mass balance discrepancy and its seasonal shift cannot be explained by measurement uncertainty; instead the discrepancy is due to combination of retained aerosol water on the conditioned FRM filters and volatilization losses. The relative importance of these different effects varies with aerosol composition and causes the observed seasonal variation in the mass balance. The contribution of the aerosol water to the FRM-measured mass is estimated using continuous measurements of aerosol water at the site; volatilization losses are estimated from other filter-based instruments. Water contributes 16% of the FRM mass in the summer, and 8% of the FRM mass in the winter; it also appears responsible for episodes where the FRM-measured mass is significantly greater than the sum of components. Retention of water is greatest during acidic conditions, which commonly occur during the summer months. Volatilization losses are estimated at 5% of the FRM mass during the summer, and 9% for the winter. Volatilization losses appear to be most significant on days dominated by organic aerosol, or winter days with relatively high nitrate concentration. Accounting for the effects of water and volatilization losses closes the mass balance between the FRM and the sum of the chemical components, providing insight into the FRM measurements. r

Spatial and Temporal Variation of Chemical Composition and Mass Closure of Ambient PM10 in Tianjin, China

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Chemical Characterization and Mass Closure of Fine Aerosol for Different Land Use Patterns in Mumbai City

“…In the United States, the contributions of sulphate-30%, OM-31%, EC-4%, crustal -10%, were estimated at Cincinnati whereas contributions of OM-23%, EC-3%, SIA-45%, crustal-10% at Pittsburgh were observed (Martuzevicius et al, 2004;Rees et al, 2004). In Shanghai, China, OC-30%, SIA-40% and crustal 10% were observed while in Macao, China, OM-40%, EC-7%, SIA-28% were determined (Wu et al, 2003).…”

A mass closure and PMF source apportionment study on the sub-micron sized aerosol fraction at urban sites in Italy

“…OM was the major contributor during both seasons, accounting for a large part of PM1 mass (about 40% on average); EC percentages were comparable at all sites during both seasons (about 4%). The unaccounted mass fraction (14-22%) given by the chemical mass balance resulted from aerosol-bound water, minor components, and measurement errors evaluated in 10% following Rees et al (2004).…”