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Organic aerosol (OA) is a significant constituent of urban particulate matter (PM), and molecular markers therein provide information on the sources and formation mechanisms. With the in situ measurement of over 70 OA molecular markers in a summer month at a bihourly resolution, this study focused on the temporal variations in representative markers and dynamic source contributions to OA at an urban site in Hong Kong SAR (HK). The levels of secondary OA (SOA) markers were markedly elevated (p < 0.05) in the short-duration cases with continental and coastal air relative to those in the most common marine air, and the primary markers primarily contained local characteristics. The troughs showed the enhancements of many SOA markers (p < 0.05), which appeared to be related to the high relative humidity. The diurnal patterns of 2-methyltetrols varied in differed cases, and their aqueous formation at night seemed plausible, particularly in the presence of troughs. Eight sources were identified for the organic matter in submicron PM (PM1 -OM). Despite being an urban site, the mean SOA contribution (66.1 ± 10.5 %), primarily anthropogenic, was significant. Anthropogenic SOA dominated in the cases with continental and coastal air and in the early afternoon. Local cooking and vehicle emissions became predominant in the case of marine air without troughs. Even averaged over the study period in this summer month with the prevalence of marine air, primary cooking emissions contributed up to 44.2 % to PM1 -OM in the early evening. The study highlighted the need to control regional anthropogenic SOA and local cooking emissions to mitigate PM pollution in HK. [ABSTRACT FROM AUTHOR]

Organic aerosol (OA) is a significant constituent of urban particulate matter (PM), and molecular markers therein provide information on sources and formation mechanisms of OA. With in-situ measurement of over 70 OA molecular markers at a bihourly resolution, this study focused on the temporal variations of representative markers and dynamic source contributions to OA at an urban site in Hong Kong. The levels of secondary OA (SOA) markers were markedly elevated in continental and coastal air, and the primary markers were more of local characteristics. The diurnal patterns of 2-methyltetrols differed between scenarios, and their aqueous formation at night seemed plausible, particularly in the presence of troughs. Seven unambiguous sources were identified for the organic matters in submicron PM (PM1-OM). Despite an urban site, the SOA contribution (49 ± 8 %), primarily anthropogenic, was significant. Anthropogenic SOA dominated in continental and coastal air and in early afternoon. Local cooking and vehicle emissions became predominant in the scenario of marine air without troughs. Even averaged over the study period, cooking emissions contributed up to 40 % to PM1-OM in the early evening. The study highlighted the need to control regional anthropogenic SOA and local cooking emissions to mitigate PM pollution in Hong Kong. [ABSTRACT FROM AUTHOR]

Due to the high health risks associated with indoor air pollutants and long‐term exposure, indoor air quality has received increasing attention. In this study, we put emphasis on the molecular composition, source emissions, and chemical aging of air pollutants in a residence with designed activities mimicking ordinary Hong Kong homes. More than 150 air pollutants were detected at molecular level, 87 of which were quantified at a time resolution of not less than 1 hour. The indoor‐to‐outdoor ratios were higher than 1 for most of the primary air pollutants, due to emissions of indoor activities and indoor backgrounds (especially for aldehydes). In contrast, many secondary air pollutants exhibited higher concentrations in outdoor air. Painting ranked first in aldehyde emissions, which also caused great enhancement of aromatics. Incense burning had the highest emissions of particle‐phase organics, with vanillic acid and syringic acid as markers. The other noteworthy fingerprints enabled by online measurements included linoleic acid, cholesterol, and oleic acid for cooking, 2,5‐dimethylfuran, stigmasterol, iso‐/anteiso‐alkanes, and fructose isomers for smoking, C28‐C34 even n‐alkanes for candle burning, and monoterpenes for the use of air freshener, cleaning agents, and camphor oil. We showed clear evidence of chemical aging of cooking emissions, giving a hint of indoor heterogeneous chemistry. This study highlights the value of organic molecules measured at high time resolutions in enhancing our knowledge on indoor air quality. [ABSTRACT FROM AUTHOR]

Understanding the formation mechanisms of secondary organic aerosols (SOA) is an arduous task in atmospheric chemistry. In November 2018, a sampling campaign was conducted at an urban background site in Hong Kong for characterization of secondary air pollution. A high-resolution time-of-flight aerosol mass spectrometer was used to monitor the compositions of non-refractory submicron particulate matters (NR-PM 1), and multiple online instruments provided us with comprehensive auxiliary data. Organic aerosol (OA) constituted the largest fraction (43.8%) of NR-PM 1 , and 86.5% of the organics was contributed by the oxygenated OA (OOA, secondary components). Formation mechanisms of a dominant and more variable component of the less-oxidized OOA (labelled as LO-OOA1 in this study) and the more-oxidized OOA (MO-OOA) were explored. Based on the multilinear regression with molecular markers of OA (e.g., hydroxybenzonic acids and 2,3-dihydroxy-4-oxopentanoic acid), we presumed that anthropogenic organic compounds, especially aromatics, were the most likely precursors of LO-OOA1. MO-OOA correlated well with odd oxygen (O x), and its concentration responded positively to the increase of liquid water content (LWC) in NR-PM 1 , indicating that the formation of MO-OOA involved photochemical oxidation and aqueous processes. It exhibited the best correlation with malic acid which can be formed through the oxidation of various precursors. Moreover, it was plausible that LO-OOA1 was further oxidized to MO-OOA through aqueous processes, as indicated by the consistent diurnal variations of MO-OOA to LO-OOA1 ratio and LWC. This study highlights the important roles of anthropogenic emissions and aqueous processes in SOA formation in coastal areas downwind of cities. [Display omitted] • OA with the dominance of SOA made up the bulk of NR-PM1. • Aromatics were the likely precursors of the dominant LO-OOA component. • Photochemical and aqueous processes were involved in the formation of MO-OOA. [ABSTRACT FROM AUTHOR]

A sampling campaign was conducted at an urban roadside site in Hong Kong from Nov. to Dec. in 2017 using a suite of state-of-the-art instruments to monitor compositions of non-refractory sub-micron particulate matter (NR-PM 1) and gaseous pollutants. Results showed that the average NR-PM 1 concentration was 26.1 ± 0.7 μg/m3 (average ± 95% confidence interval) and organic aerosol (OA) contributed the most to NR-PM 1 with a proportion of 57.7 ± 0.2%. The aerosol size distributions of bulk composition of NR-PM 1 presented a peak at ~600 nm with internal mixtures of the organic and inorganic components, while there were a larger proportion of primary organic particles at < 200 nm, indicating intensive emissions of primary organics at this site. Positive matrix factorization (PMF) analysis was applied to the measurement data and four OA components were identified, including a hydrocarbon-like OA (HOA) factor, a cooking organic aerosol (COA) factor and two oxygenated OA (OOA) factors of different oxidation levels: less oxidized OOA (LO-OOA) and more oxidized OOA (MO-OOA). Strikingly, the contribution of MO-OOA was the highest (30.9 ± 0.4%), suggesting high oxidation degree and/or high regional background in the roadside environment. Moreover, the proportion of COA reached 25.4 ± 0.3% at this roadside site with heavy traffic fleet, which was even higher than the percentage of HOA (p < 0.01). The average ratio of C 3 H 3 O + / C 3 H 5 O + (2.01 ± 0.01) and the opposite pattern of C 3 H 3 O + / C 3 H 5 O + to O x during daytime hours suggested that the COA was oxidized to some extent when transported to the site. The findings implied that cooking activities are a significant source of organic aerosols in Hong Kong, even at a busy road. Control measures should focus on both cooking and traffic emissions in Hong Kong. [Display omitted] • The proportion of COA in NR-PM 1 was higher than HOA at this traffic-busy site. • The pattern of C 3 H 3 O + / C 3 H 5 O + ratio was opposite to the trend of O x during daytime hours. • Cooking activities are a significant source of organic aerosols in Hong Kong. [ABSTRACT FROM AUTHOR]