Hourly Measurements of Organic Molecular Markers in Urban Shanghai, China: Primary Organic Aerosol Source Identification and Observation of Cooking Aerosol Aging

Abstract

Molecular markers in ambient organic aerosol (OA) provide highly specific source information. Their traditional quantification is based on offline analysis of filter samples, and the coarse time resolution and labor-intensive nature hugely limit the utility of the tracer data. In this study, hourly organic molecular markers in fine particulate matter were measured using a recently commercialized thermal desorption aerosol gas chromatography− mass spectrometry (TAG) technique at an urban location in Shanghai, China during a three-week campaign from 9 November to 3 December, 2018. Selected primary OA molecular markers, including anhydrosugars, fatty acids, aromatic acids, and polycyclic aromatic hydrocarbons (PAHs), were examined in detail. Their diurnal variations showed characteristic features representing the corresponding emission source activities. For example, stearic acid showed a clear peak around 7 pm, in accordance with the enhanced cooking activities during mealtime. Diagnostic ratios of related makers of different reactivities provided unique information in uncovering the source information and tracking evolution of the OA in the atmosphere, for example, ratios of levoglucosan to its isomers and K + identified crop residue burning as the major form of biomass burning (BB). Ratios of unsaturated and saturated fatty acids gave unambiguous indication of atmospheric degradation of unsaturated fatty acids after emissions. Oleic acid to stearic acid ratios in ambient data (0.83 ± 0.54) were lower than those in the source profiles (1.2−6.5). Furthermore, the oleic acid to stearic acid ratio was found to be highly correlated with O/C ratios (R p : −0.66), suggesting the possible utility of oleic acid as a model compound to examine the heterogeneous reaction of cooking-related OA. PAH ratio−ratio plots helped identify varying influences of major combustion sources associated with air masses of different origins, revealing that BB and coal combustion were dominant under the influence of long-range transport air mass, while vehicle emissions were dominant under local/median-range air mass influence. This study demonstrated the utility of high time-resolution organic markers in capturing the dynamic change of source emissions and atmospheric aging, providing observational evidence to support their use in source apportionment.

Atmospheric conditions and composition that influence PM<sub>2.5</sub> oxidative potential in Beijing, China

“…The sample from 22 November 2016 has a particularly high concentration of cooking markers (palmitic acid, stearic acid and cholesterol). This could reflect the fact that the traditional Chinese winter solar term Xiao Xue (小雪, “light snow”) begins on this date ( Li, 2006 ), a period associated with the preparation of warm foods as the ambient temperatures in northern China drop; a similar elevation of palmitic acid and stearic acid has been observed around the same week in a more recent study in Shanghai ( Q. Wang et al, 2020 ).…”

Chemical characterization of oxygenated organic compounds in the gas phase and particle phase using iodide CIMS with FIGAERO in urban air

“…Nitrophenols (C 6 H 5 NO 3 I − ), methyl nitrophenols (C 7 H 7 NO 3 I − ) and dinitrophenols (C 6 H 4 N 2 O 5 I − ) were the Wang et al (2016) most significant components of nitro-aromatics in the gas phase. Despite the fact that nitrated phenols could be formed by photochemical oxidation of their aromatic hydrocarbon precursors (Z.…”

“…There is a growing interest in N 2 O 5 and its product nitryl chloride (ClNO 2 ) because ClNO 2 is found to serve as a nocturnal reservoir of Cl radical and reactive nitrogen, and hence enhance the ozone formation the next day (Osthoff et al, 2008;Wang et al, 2016). Time series of N 2 O 5 and ClNO 2 exhibited two patterns.…”

Atmospheric conditions and composition that influence PM<sub>2.5</sub> oxidative potential in Beijing, China

“…The sample from 22 November 2016 has a particularly high concentration of cooking markers (palmitic acid, stearic acid and cholesterol). This could reflect the fact that the traditional Chinese winter solar term Xiao Xue (小雪,"Light Snow"), begins on this date (Li, 2006), a period associated with the preparation of warm foods as the ambient temperatures in northern China drop; a similar elevation of palmitic acid and stearic acid has been observed around the same week in a more recent study in Shanghai (Wang et al, 2020c).…”