Analysis of polycyclic aromatic hydrocarbons and derivatives in ambient aerosols using 1-D and 2-D gas chromatography-mass spectrometry methods

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are a family of toxic yet highly persistent compounds widely distributed in the atmosphere. The occurrence of PAHs in ambient air is a significant concern because of their carcinogenicity, teratogenicity, and genotoxicity. PAHs can be produced from almost all kinds of combustion involving organic materials, both natural sources and anthropogenic sources. Thus, it is of higher priority to monitor these components in environmental samples. In this thesis work, two analytical methods involving 1-D and 2-D gas chromatography-mass spectrometry were used to quantify PAHs in ambient particulate matter samples. Thermal desorption gas chromatography coupled with a quadrupole mass spectrometry (TD-GC/MS) was used to analyze nonpolar organic compounds (NPOCs) in 55 PM_2.5 samples collected in Thailand. The quantified NPOCs include 25 PAHs, 30 alkanes, 15 hopanes, and 9 steranes. Total NPOCs ranged from 9.7 to 199.6 ng m^-3, accounting for 0.35% of total organic carbon mass, and PAHs ranged from 0.35 to 6.23 ng m^-3. Alkanes contributed most to the total NPOC concentrations (95.0%), followed by PAHs and hopanes and steranes. Among PAHs, the higher molecular weight PAHs dominated. Source analysis using the ratio-ratio plots of PAH isomers normalized by elemental carbon (EC) showed that biomass burning is the dominant source for PAHs. Carbon preference index analysis of alkanes also showed that biomass burning is likely to be the dominant source of alkanes. The ratio-ratio plot of hopanes normalized by EC showed that diesel vehicles exhaust is the dominant source for hopanes. But the low concentration of hopanes and steranes indicates that vehicle emission contributes little to the PM_2.5 of the samples. Comprehensive two-dimensional gas chromatography coupled with a time-of-flight mass spectrometer (GC×GC-TOF) was used to analyze 17 PM_2.5 samples collected at multiple locations in Shanghai. A total of 20 polyphenyls or phenyl-PAHs and 69 short chain alkyl-PAHs were found in 17 ambient samples. Semi-quantitative analysis was conducted to determine their atmospheric concentrations. The abundance of substituted PAHs including polyphenyls, phenyl-PAHs and alkyl-PAHs is much lower than their parent PAHs. The spatial distributions indicated that Chemical industry area site (CIA) winter samples showed the highest abundance of polyphenyls and phenyl-PAHs, possibly hinting that chemical industry area site is associated with intensive source emissions. All polyphenyls, phenyl-PAHs or alkyl-PAHs and their corresponding parent PAHs showed good correlations, suggesting their commonality in contributing sources. Although abundance of polyphenyls, phenyl-PAHs and alkyl-PAHs are much lower than their parent PAHs, they may affect the secondary organic aerosol formation due to the higher reactivity with OH radical. In future work, more efforts are suggested to focus on more accurate quantitative analysis of the PAH derivatives. Meanwhile, we should continue to identify more multi-substituent alkyl-PAHs. At last, measurement data for the rate constant of most of the polyphenyls, phenyl-PAHs and alkyl-PAHs detected in this work are not available. Thus, quantitative structure–activity relationship models could be explored for prediction of the reaction rate constants of newfound PAH derivatives with hydroxyl radicals so that their atmospheric lifetime can be assessed.

Date of Award	2020
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology