Particulate matter formation from volatile chemical products including combustion and non-combustion sources

Date

2018-10-09

Authors

Dhulipala, Surya Venkatesh

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Abstract

New evidence on the contribution of volatile chemical products from non-combustion sources to ambient particulate matter formation has renewed interest in policy-makers and atmospheric scientists to quantify these emissions which have historically been under-reported. In this dissertation, several representative compounds are chosen to provide a holistic comparison of particulate matter formation from both combustion and non-combustion sources. For this purpose, an environmental chamber is employed with state-of-art-instruments to monitor the formation and decay of air pollutants in the gas-phase and particle-phase. The Aerosol Chemical Speciation Monitor (ACSM) is used to measure the total concentration and bulk composition of particulate matter less than 1 µm in size (PM₁). The High Resolution Time-of-Flight-Mass-Spectrometer (HR-Tof-CIMS) along with a Filter Inlet for Aerosols and Gases (FIGAERO) is used to measure the gas-phase composition in real-time and the particle-phase composition in a semi-continuous manner. Toluene, an aromatic compound, is commonly used in solvents. Its reaction with OH radicals, the most abundant radical in the atmosphere, is well understood but its reaction with chlorine radicals is not. Chlorine is an important oxidant in both in-land and coastal areas. Here, high oxidative states of organic aerosol (component of PM) and gas-phase products formed during toluene-Cl photo-oxidation are reported. Secondary OH radical production is also observed. Long-chain alkanes are associated with vehicular exhaust and their reactions with chlorine also remain poorly understood. Here, the Cl-initiated photo-oxidation of alkanes with 10 carbons – n-decane, 2-methyl nonane and butyl cyclohexane are reported under low NO [subscript x] environments and variable relative humidity (0% and 35-55%). Presence of gas-phase and particle-products associated with OH radical chemistry are reported in the presence of chlorine. A class of compounds defined as Low Vapor Pressure Volatile Organic Compounds (LVP-VOCs) by policy-makers and referred to as Intermediate-Volatility Organic Compounds (IVOCs) by atmospheric scientists includes commercial grade mineral spirits, diethylene mono butyl glycol ether (DEGBE) and Texanol®, which are commonly used in solvents and coatings. Here, the Cl- and OH-radical initiated particulate matter formation from these IVOCs are discussed and compared to alkanes of similar volatility but originating from a combustion source (n-pentadecane and 2,6,10 trimethyl dodecane).

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