Abstract

Abstract. Submicron aerosol particles (PM1) were measured in-situ using a High-Resolution Time-of-Flight Aerosol Mass Spectrometer during the summer 2009 Field Intensive Study at Queens College in New York, NY. Organic aerosol (OA) and sulfate are the two dominant species, accounting for 54% and 24%, respectively, of the total PM1 mass. The average mass-based size distribution of OA presents a small mode peaking at ~150 nm (Dva) and an accumulation mode (~550 nm) that is internally mixed with sulfate, nitrate, and ammonium. The diurnal cycles of both sulfate and OA peak between 01:00–02:00 p.m. EST due to photochemical production. The average (±σ) oxygen-to-carbon (O/C), hydrogen-to-carbon (H/C), and nitrogen-to-carbon (N/C) ratios of OA in NYC are 0.36 (±0.09), 1.49 (±0.08), and 0.012 (±0.005), respectively, corresponding to an average organic mass-to-carbon (OM/OC) ratio of 1.62 (±0.11). Positive matrix factorization (PMF) of the high resolution mass spectra identified two primary OA (POA) sources, traffic and cooking, and three secondary OA (SOA) components including a highly oxidized, regional low-volatility oxygenated OA (LV-OOA; O/C = 0.63), a less oxidized, semi-volatile SV-OOA (O/C = 0.38) and a unique nitrogen-enriched OA (NOA; N/C = 0.053) characterized with prominent CxH2x + 2N+ peaks likely from amino compounds. Our results indicate that cooking and traffic are two distinct and mass-equivalent POA sources in NYC, together contributing ~30% of the total OA mass during this study. The OA composition is dominated by secondary species, especially during high PM events. SV-OOA and LV-OOA on average account for 34% and 30%, respectively, of the total OA mass. The chemical evolution of SOA in NYC appears to progress with a continuous oxidation from SV-OOA to LV-OOA, which is further supported by a gradual increase of O/C ratio and a simultaneous decrease of H/C ratio in total OOA. Detailed analysis of NOA (5.8% of OA) presents evidence that organic nitrogen species such as amines might have played an important role in the atmospheric processing of OA in NYC, likely involving both acid-base chemistry and photochemistry. In addition, analysis of air mass trajectories and satellite imagery of aerosol optical depth (AOD) indicates that the high potential source regions of secondary sulfate and aged OA are mainly located in regions to the west and southwest of the city.

Highlights

  • Aerosol particles play significant roles in climate change by altering the radiative balance of the Earth’s atmosphere directly and indirectly (IPCC, 2007)

  • We report the main findings from this study, including (1) evaluation of HR-AMS based on the comparisons of measurements with collocated instruments; (2) mass concentrations, size distributions, chemical composition, and temporal and diurnal variations of PM1 species; (3) elemental composition of Organic aerosol (OA); and (4) characteristics and dynamic variations of OA components determined via Positive Matrix Factorization (PMF) of the high-resolution mass spectra (HRMS)

  • SV-oxygenated OA (OOA) contributes 42% of the CxHyO+1 signal and 31% of the CxHyO+2 (Fig. 10). These results clearly indicate that the chemical compositions of the two OOA types are significantly different: semi-volatile OOA (SV-OOA) comprises less oxygenated, possibly freshly oxidized species, while low-volatility oxygenated OA (LV-OOA) comprises highly oxidized species including di- and poly-carboxylic acids

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Summary

Introduction

Aerosol particles play significant roles in climate change by altering the radiative balance of the Earth’s atmosphere directly and indirectly (IPCC, 2007). They constitute a threat to public health by increasing the risk of morbidity and mortality of sensitive groups (Pope et al, 2002, 2009). Fine particulate matter (PM) in densely populated megacity. The New York City (NYC) metropolitan area is one of the most populous megacities in the world and among the most polluted cities in the US by fine PM and ozone (American Lung Association’s Report, 2010). Characterizing the chemical composition and dynamic variations of aerosols in large urban environments such as NYC is important to unravel the complexities of anthropogenic aerosols and supporting health outcome studies (Demerjian and Mohnen, 2008; Wexler and Johnston, 2008)

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