Nonpolar organic compounds in fine particles: quantification by thermal desorption–GC/MS and evidence for their significant oxidation in ambient aerosols in Hong Kong

Abstract

Nonpolar organic compounds (NPOCs) in ambient particulate matter (PM) commonly include n-alkanes, branched alkanes, hopanes and steranes, and polycyclic aromatic hydrocarbons (PAHs). The recent development of thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) has greatly reduced time and labor in their quantification by eliminating the laborious solvent extraction and sample concentration steps in the traditional approach that relies on solvent extraction. The simplicity of the TD-GCMS methods has afforded us concentration data of NPOCs in more than 90 aerosol samples in two aerosol field studies and 20 vehicular emissions-dominated source samples in Hong Kong over the past few years. In this work, we examine the interspecies relationships between select NPOCs and their concentration ratios to elemental carbon (EC) among the ambient samples and among the source samples. Our analysis indicates that hopanes were mainly from vehicular emissions and they were significantly oxidized in ambient PM. The hopane/EC ratio in ambient samples was on average less than half of the ratio in vehicular emissions-dominated source samples. This highlights the necessity in considering oxidation loss in applying organic tracer data in source apportionment studies. Select PAH/EC ratio-ratio plots reveal that PAHs had diverse sources and vehicular emissions were unlikely a dominant source for PAHs in Hong Kong. Biomass burning and other regional sources likely dominated ambient PAHs in Hong Kong.

Nonpolar organic compounds as PM2.5 source tracers: Investigation of their sources and degradation in the Pearl River Delta, China

“…This indicates that vehicle exhaust is likely a dominant source for hopanes at these sites. Yu et al [] found similar results of vehicle emissions dominating ambient hopane concentrations at sites nearby in Hong Kong. However, much of the data in this study are at higher hopane/EC ratios than the Zhujiang tunnel profile, which that either the vehicle emission contribution favors the gasoline profile more than the tunnel data or an additional source is influencing the ambient data.…”

“…The primary component (i.e., directly emitted) of carbonaceous material collected at urban sites typically contributes about 30-60% to the total organics in the aerosol [Kuang et al, 2015;Zhao et al, 2009]. Among the primary components, nonpolar organic compounds (NPOCs) have been widely studied due to their use as source indicators and relative ease of analysis [Bi et al, 2003;Xu et al, 2013;Yadav et al, 2013;Yu et al, 2011;Zheng et al, 2000Zheng et al, , 2006. NPOCs aside, a number of polar organic compounds are also unique source tracers for PM 2.5 , such as levoglucosan, which is uniquely emitted by biomass-burning activities [Engling et al, 2006], and β-caryophyllinic acid, the tracer for the β-caryophyllene-derived secondary organic aerosol other polar organic tracers is more laborious and expensive, severely limiting their use in source apportionment studies.…”

Non-polar organic compounds in autumn and winter aerosols in a typical city of eastern China: size distribution and impact of gas–particle partitioning on PM<sub>2.5</sub> source apportionment

“…There were several deviation points in the lower-left corner, and the values were smaller than the values of the tunnel and vehicle source profile, indicating mixed influence from traffic origins and degradation. Yu et al (2011) reported a more apparent linear distribution of data sets measured in Hong Kong and PRD, which can be attributed to their single vehicle source type.…”

“…Photochemical oxidation has great influences on the mass concentration and size-specific distribution of NPOCs, as well as on their removal and atmospheric fate (May et al, 2012). Photochemical decay could cause the ambient data to be distributed along a line emanating from the source profile in the ratio-ratio plot, with increasing photochemical age (Robinson et al, 2006;Yu et al 2011). EC shares common origins with PAHs and hopanes but they are subject to photodegradation.…”

Road tunnel, roadside, and urban background measurements of aliphatic compounds in size-segregated particulate matter

“…At high concentrations, acute eczema of the skin and pulmonary edema may develop. Alkanes have also been found to penetrate rapidly into the fatty cells of the myelin sheath that surrounds nerve fibres, where they dissolve the cells and cause degeneration of the axons, interrupting the transference of impulses (Yu et al, 2011a). Alkenes are not found in crude petroleum but are present in some refined products, particularly in gasoline.…”