Receptor modeling of near-roadway aerosol mass spectrometer data in Las Vegas, Nevada, with EPA PMF

S G Brown,P T Roberts,T Lee,J L Collett,P Paatero,G A Norris,D R Worsnop

doi:10.5194/acp-12-309-2012

Abstract

Abstract. Ambient non-refractory PM1 aerosol particles were measured with an Aerodyne High Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-AMS) at an elementary school 18 m from the US 95 freeway soundwall in Las Vegas, Nevada, during January 2008. Additional collocated continuous measurements of black carbon (BC), carbon monoxide (CO), nitrogen oxides (NOx), and meteorological data were collected. The US~Environmental Protection Agency's (EPA) positive matrix factorization (PMF) data analysis tool was used to apportion organic matter (OM) as measured by HR-AMS, and rotational tools in EPA PMF were used to better characterize the solution space and pull resolved factors toward known source profiles. Three- to six-factor solutions were resolved. The four-factor solution was the most interpretable, with the typical AMS PMF factors of hydrocarbon-like organic aerosol (HOA), low-volatility oxygenated organic aerosol (LV-OOA), biomass burning organic aerosol (BBOA), and semi-volatile oxygenated organic aerosol (SV-OOA). When the measurement site was downwind of the freeway, HOA composed about half the OM, with SV-OOA and LV-OOA accounting for the rest. Attempts to pull the PMF factor profiles toward source profiles were successful but did not qualitatively change the results, indicating that these factors are very stable. Oblique edges were present in G-space plots, suggesting that the obtained rotation may not be the most plausible one. Since solutions found by pulling the profiles or using Fpeak retained these oblique edges, there appears to be little rotational freedom in the base solution. On average, HOA made up 26% of the OM, while LV-OOA was highest in the afternoon and accounted for 26% of the OM. BBOA occurred in the evening hours, was predominantly from the residential area to the north, and on average constituted 12% of the OM; SV-OOA accounted for the remaining third of the OM. Use of the pulling techniques available in EPA PMF and ME-2 suggested that the four-factor solution was very stable.

Highlights

A number of studies have demonstrated the significant health impacts of air pollution such as particulate matter of aerodynamic diameter less than 2.5 microns (PM2.5), including increased asthma rates, detrimental fetal development during pregnancy, and decreased lung capacity (Brunekreef et al, 1997; McDonald et al, 2004; Dockery et al, 1993; Dockery and Stone, 2007)
Aerosol Mass Spectrometer (AMS) fragments associated with oxygenated organic aerosol (OOA), such as m/z 44 (COO+), showed only minor fluctuations throughout the day, while those used as tracers of biomass burning, such as m/z
Since black carbon (BC) and carbon monoxide (CO) are from primary emissions and Organic matter (OM) is a mixture of primary emissions and secondary products of atmospheric reactions, the modest correlations among these parameters suggest that a large fraction of the OM may be secondary in nature

Summary

Introduction

A number of studies have demonstrated the significant health impacts of air pollution such as particulate matter of aerodynamic diameter less than 2.5 microns (PM2.5), including increased asthma rates, detrimental fetal development during pregnancy, and decreased lung capacity (Brunekreef et al, 1997; McDonald et al, 2004; Dockery et al, 1993; Dockery and Stone, 2007). OM is a complicated mixture of thousands of individual molecules and is a combination of both primary particulate emissions and secondary aerosol formed from gaseous precursors. It is a major component of vehicular exhaust emissions and, in addition to being a large part of PM2.5 mass, includes polycyclic aromatic hydrocarbons (PAHs), which are carcinogenic (Larsen and Baker, 2003; Lobscheid and McKone, 2004; Adonis et al, 2003; Flowers et al, 2002)

Methods

Results

Discussion

Conclusion