Chemical composition and redox activity of PM0.25 near Los Angeles International Airport and comparisons to an urban traffic site

Farimah Shirmohammadi; Christopher Lovett; Mohammad Hossein Sowlat; Amirhosein Mousavi; Vishal Verma; Martin M Shafer; James J Schauer; Constantinos Sioutas

doi:10.1016/j.scitotenv.2017.08.239

Chemical composition and redox activity of PM_0.25 near Los Angeles International Airport and comparisons to an urban traffic site

Sci Total Environ. 2018 Jan 1:610-611:1336-1346. doi: 10.1016/j.scitotenv.2017.08.239. Epub 2017 Aug 30.

Authors

Farimah Shirmohammadi¹, Christopher Lovett¹, Mohammad Hossein Sowlat¹, Amirhosein Mousavi¹, Vishal Verma², Martin M Shafer³, James J Schauer⁴, Constantinos Sioutas⁵

Affiliations

¹ University of Southern California, Department of Civil and Environmental Engineering, Los Angeles, CA, USA.
² University of Illinois at Urbana-Champaign, Department of Civil and Environmental Engineering, Urbana-Champaign, IL, USA.
³ University of Wisconsin-Madison, Environmental Chemistry and Technology Program, Madison, WI, USA.
⁴ University of Wisconsin-Madison, Environmental Chemistry and Technology Program, Madison, WI, USA; University of Wisconsin-Madison, Department of Civil and Environmental Engineering, Madison, WI, USA.
⁵ University of Southern California, Department of Civil and Environmental Engineering, Los Angeles, CA, USA. Electronic address: sioutas@usc.edu.

PMID: 28873663
DOI: 10.1016/j.scitotenv.2017.08.239

Abstract

To investigate the relative impacts of emissions from Los Angeles International Airport (LAX), as well as the impacts of traffic emissions from freeways, on the oxidative potential of particulate matter (PM), PM_0.25 were collected at two urban background locations in Los Angeles. Redox activity of the PM samples was measured by means of an in vitro alveolar macrophage assay that quantifies the formation of reactive oxygen species (ROS) in cells, and detailed chemical analyses were performed to determine the speciated chemical composition of collected PM. A molecular marker-based chemical mass balance (MM-CMB) model was applied to estimate the relative contributions from the following primary sources to the organic carbon (OC) component of PM: mobile sources (combined gasoline and diesel vehicles), wood smoke, vegetative detritus, road dust and ship emissions. A source profile of aircraft emissions was not included in the model; however its contribution was estimated from un-apportioned primary OC in the MM-CMB model ("other OC") after accounting for the contribution of secondary organic carbon (SOC) to OC. The contribution of mobile sources to OC was 82% and 28% at the central Los Angeles site (freeway emissions) and the LAX site, respectively. The estimated contribution of aircraft emissions to PM_0.25 OC was 36% at the LAX site. ROS activity levels showed little spatial variability, with no statistically significant difference between the averages observed at LAX (24.75±4.01μgZymosan/m³) and central Los Angeles (27.77±2 0.32μgZymosan/m³), suggesting similar levels of inhalation exposure to redox active species of PM_0.25. A multiple linear regression analysis indicated that the variability in ROS activity is best explained by the chemical markers of major identified sources: EC emitted by traffic, and sulfur, considered in our study as a potential tracer of aircraft emissions, with statistically significantly higher concentrations of sulfur at the LAX site (p<0.001).

Keywords: Aircraft emissions; Oxidative potential; PM(0.25); Ultrafine particles; Vehicle exhaust emissions.