Composition and sources of fine and coarse particles collected during 2002–2010 in Boston, MA

Abstract

Identifying the sources, composition, and temporal variability of fine (PM_2.5) and coarse (PM_2.5–10) particles is a crucial component in understanding particulate matter (PM) toxicity and establishing proper PM regulations. In this study, a Harvard Impactor was used to collect daily integrated fine and coarse particle samples every third day for 9 years at a single site in Boston, MA. In total, 1,960 filters were analyzed for elements, black carbon (BC), and total PM mass. Positive Matrix Factorization (PMF) was used to identify source types and quantify their contributions to ambient PM_2.5 and PM_2.5–10. BC and 17 elements were identified as the main constituents in our samples. Results showed that BC, S, and Pb were associated exclusively with the fine particle mode, while 84% of V and 79% of Ni were associated with this mode. Elements mostly found in the coarse mode, over 80%, included Ca, Mn (road dust), and Cl (sea salt). PMF identified six source types for PM_2.5 and three source types for PM_2.5–10. Source types for PM_2.5 included regional pollution, motor vehicles, sea salt, crustal/road dust, oil combustion, and wood burning. Regional pollution contributed the most, accounting for 48% of total PM_2.5 mass, followed by motor vehicles (21%) and wood burning (19%). Source types for PM_2.5–10 included crustal/road dust (62%), motor vehicles (22%), and sea salt (16%). A linear decrease in PM concentrations with time was observed for both fine (–5.2%/yr) and coarse (–3.6%/yr) particles. The fine-mode trend was mostly related to oil combustion and regional pollution contributions. Average PM_2.5 concentrations peaked in summer (10.4 µg/m³), while PM_2.5–10 concentrations were lower and demonstrated little seasonal variability. The findings of this study show that PM_2.5 is decreasing more sharply than PM_2.5–10 over time. This suggests the increasing importance of PM_2.5–10 and traffic-related sources for PM exposure and future policies.

Implications: Although many studies have examined fine and coarse particle composition and sources, few studies have used concurrent measurements of these two fractions. Our analysis suggests that fine and coarse particles exhibit distinct compositions and sources. With better knowledge of the compositional and source differences between these two PM fractions, better decisions can be made about PM regulations. Further, such information is valuable in enabling epidemiologists to understand the ensuing health implications of PM exposure.

Additional information

Funding

This work was supported by the EPA Center for Particle Health Effects at the Harvard School of Public Health (grant RD-83479801-2), a National Institute of Environmental Health Sciences (NIEHS) Program grant (P30-ES000002), and an Ambient Particles and Cardiac Vulnerability in Humans grant (P01-ES009825). However, any opinions, findings, conclusions, or recommendations expressed herein are those of the authors and do not necessarily reflect the views of the supporters. Further, our supporters do not endorse the purchase of any commercial products or services mentioned in this publication.

Notes on contributors

Shahir Masri

Shahir Masri is a doctoral student, Choong-Min Kang is a research associate, and Petros Koutrakis is a professor in the Department of Environmental Health, Harvard School of Public Health, Boston, MA.