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Chemical Composition of Atmospheric Aerosols in Air Quality Field Measurements Using a Compact Time-of-Flight Aerosol Mass Spectrometer

  • Author(s): Vu, Kennedy- Kiet Tuan
  • Advisor(s): Bahreini, Roya
  • et al.
Abstract

Atmospheric aerosols affect climate, ecosystems, visibility, and human health. However, aerosol sources, atmospheric processing and climate effects still have significant uncertainties. Aerosols have a variety of characteristics, in terms of size, morphology, optical properties, and chemical composition owing to their complex nature.

The presented work in this thesis summarizes measurements carried out in Mira Loma, CA (2013) and the Colorado Front Range (2014) with the aim to better characterize the local air quality by quantifying the aerosol composition and extinction properties. Here, this thesis will address:

(1) Summertime ambient aerosol composition and extinction in Mira Loma, California.

In Southern California, pollution is primarily caused by emissions from transportation sources, and are also influenced by topography and meteorology in the area. Specifically, in the Inland Empire, warm, and dry climate promotes the formation of ozone during summer months and eastern portions of the region trap pollution due to mountain induced topography. Aimed with the goal to characterize and understand the summertime composition of ambient aerosols, and the dominant aerosol composition driving aerosol optical extinction (ext), we conducted ground-based measurements from August 17 – September 22, 2013 at the Mira Loma South Coast Air Quality Management District site. OA (54%) was found to be the most dominate aerosol non-refractory species, followed by nitrate (20%) and sulfate (14%). A strong correlation between optical extinction and aerosol nitrate fraction was also observed, indicating that visibility degradation in the eastern Los Angeles Basin is driven by secondary formation of inorganic ammonium nitrate rather than organic aerosol.

(2) Impacts of the Denver Cyclone on Air Quality in the Colorado Front Range during the FRAPPÉ 2014 campaign.

We present airborne measurements made aboard the NSF C-130 aircraft during the 2014 FRAPPÉ campaign. During the study, a synoptic mesoscale development termed the “Denver Cyclone” was prominent on July 27-28, 2014. The Denver Cyclone has a unique flow structure due to mountain induced circulation, making aircraft measurements critical and insightful to pollution transport patterns during this episode. Our results showed an increase in aerosol mass concentration of OA, NO3-, and SO42-, during the cyclone by as much as 40-80%. Additionally, different aerosol species were found to impact optical extinction (βext) on cyclone vs. non-cyclone periods. Specifically, during the non-cyclone period, OA was responsible for driving βext in the Denver Metropolitan area while in the presence of the cyclone, NO3- influenced βext the most.

The overarching objectives of both of these field campaigns is to gain a better understanding of the chemical and physical characteristics of atmospheric aerosols formed from different sources that are responsible for the reduction in the overall air quality. Advanced understanding of aerosol characteristics and the relationships with precursor sources is essential for determining effective emission control strategies to improve air quality.

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