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Here we conducted comprehensive chemical characterization and source apportionment of 49 PM 2.5 samples collected in Hong Kong. Besides the major aerosol constituents, 39 polar organic species, including 14 secondary organic aerosol (SOA) tracers of isoprene, monoterpenes, β -caryophyllene, and naphthalene, were quantified using gas chromatography–mass spectrometry (GC–MS). Six factors, i.e., SOA, secondary sulfate (SS), biomass burning (BB)/SOA, sea salt, marine vessels, and vehicle emissions, were apportioned by positive matrix factorization (PMF) as the major sources of ambient organic carbon (OC) in Hong Kong. The secondary formation, including OC from SOA, SS, and aging of BB plume, was the leading contributor to OC (51.4 %, 2.15 ± 1.37 µgCm-3) throughout the year. We then applied a tracer-based method (TBM) to estimate the SOA formation from the photo-oxidation of four selected precursors, and monoterpene SOA was the most abundant. A Kintecus kinetic model was used to examine the formation channels of isoprene SOA, and the aerosol-phase ring-opening reaction of isoprene epoxydiols (IEPOXs) was found to be the dominant formation pathway. Consistently, IEPOX tracers contributed 94 % to total GC–MS-quantified isoprene SOA tracers. The TBM-estimated secondary organic carbon (SOC TBM) and PMF-apportioned SOC (SOC PMF) showed similar temporal trends; however, SOC TBM only accounted for 26.5 % of SOC PMF , indicating a large fraction of ambient SOA was from other reaction pathways or precursors. Results of Pearson's R and multivariate linear regression analysis showed that NO x processing played a key role in both daytime and nighttime SOA production in the region. Moreover, sulfate had a significant positive linear relationship with SOC PMF and SS-related SOC, and particle acidity was significantly correlated with SOC from the aging of BB. [ABSTRACT FROM AUTHOR]

Humic-like substances (HULIS) are an important mixture of organic compounds, which account for a great part of water-soluble organic compounds in ambient aerosols. In this study, individual carboxylic and hydroxylic species in HULIS extracts of PM2.5 samples collected in Hong Kong during summer were measured by gas chromatography mass spectrometry with prior chemical derivatization. Significantly higher levels of HULIS were observed on days mainly impacted by regional pollution (regional days, 4.11 ± 1.76 μg m−3) than on days under local emission influences (local days, 0.56 ± 0.30 μg m−3). Positive matrix factorization was applied to identify the major sources and apportion their contributions to HULIS. Simultaneous monitoring and analysis data from four different sampling sites showed that sources of HULIS in Hong Kong were mainly regional with small spatial variations. Secondary aerosol formation (both organic and inorganic) had a predominant contribution (52.7%) to HULIS during the whole sampling period. It accounted for 1.88 ± 0.91 μg m−3 of HULIS on regional days, which was about 5 times higher than its contribution (0.39 ± 0.34 μg m−3) on local days. Of the three identified primary sources, biomass burning had the largest contribution on both regional (34.9%) and local days (24.6%). Marine vessels were also a significant contributor, especially on local days (20.3%). Vehicle exhaust, on the other hand, showed a negligible contribution to HULIS (2.1%) in Hong Kong in this study. [ABSTRACT FROM AUTHOR]

Atmospheric polycyclic aromatic hydrocarbons (PAHs) and their derivatives are of great concern due to their adverse health effects. However, source identification and apportionment of these compounds, particularly their nitrated and hydroxylated derivatives (i.e., NPAHs and OHPAHs), in fine particulate matter (PM 2.5 ) in Hong Kong are still lacking. In this study, we conducted a 1-year observation at an urban site in Hong Kong. PM 2.5 -bound PAHs and their derivatives were measured, with median concentrations of 4590, 44.4 and 31.6 pg m −3 for ∑ 21 PAHs, ∑ 13 NPAHs, and ∑ 12 OHPAHs, respectively. Higher levels were observed on regional pollution days than on long regional transport (LRT) or local emission days. Based on positive matrix factorization analysis, four sources were determined: marine vessels, vehicle emissions, biomass burning, and a mixed source of coal combustion and NPAHs secondary formation. Coal combustion and biomass burning were the major sources of PAHs, contributing over 85% of PAHs on regional and LRT days. Biomass burning was the predominant source of OHPAHs throughout the year, while NPAHs mainly originated from secondary formation and fuel combustion. For benzo[a]pyrene (BaP)-based PM 2.5 toxicity, the mixed source of coal combustion and NPAHs secondary formation was the major contributor, followed by biomass burning and vehicle emissions. [ABSTRACT FROM AUTHOR]

The correct name of the 3rd Author is presented in this paper. [ABSTRACT FROM AUTHOR]

Humic-like substances (HULIS) account for a considerable fraction of water-soluble organic matter (WSOM) in ambient fine particulates (PM 2.5) over the world. However, systemic studies regarding the chemical characteristics, sources and redox activity of HULIS are still limited. In this study, the mass concentration, optical properties, and reactive oxygen species (ROS)-generation potential of HULIS were investigated in PM 2.5 samples collected in Hong Kong during 2011–2012, and they all showed higher levels on days under regional pollution than on days under long range transport (LRT) pollution and local emissions. Positive matrix factorization (PMF) analysis was conducted regarding the mass concentration and dithiothreitol (DTT) activity of HULIS. Four primary sources (i.e. marine vessels, industrial exhaust, biomass burning, and vehicle emissions), and two secondary sources (i.e. secondary organic aerosol formation and secondary sulfate) were identified. Most sources showed higher contributions to both the mass concentration and DTT activity of HULIS on regional days than on LRT and local days, except that marine vessels had a higher contribution on local days than the other two synoptic conditions. Secondary processes were the major contributor to HULIS (54.9%) throughout the year, followed by biomass burning (27.4%) and industrial exhaust (14.7%). As for the DTT activity of HULIS, biomass burning (62.9%) and secondary processes (25.4%) were found to be the top two contributors. Intrinsic ROS-generation potential of HULIS was also investigated by normalizing the DTT activity by HULIS mass in each source. HULIS from biomass burning were the most DTT-active, followed by marine vessels; while HULIS formed through secondary processes were the least DTT-active. For the optical properties of HULIS, multiple linear regression model was adopted to evaluate the contributions of various sources to the light absorbing ability of HULIS. Biomass burning was found to be the only source significantly associated with the light absorbing property of HULIS. Image 1 • Secondary processes were the major contributor to HULIS mass concentration. • HULIS from biomass burning were the most DTT-active. • Biomass burning is the only source significantly contributing to MAE 365 of HULIS. Short Summary : HULIS in Hong Kong atmosphere showed higher light absorption ability and DTT activity on days under regional pollution than days under LRT pollution and local emissions. Biomass burning was the only source significantly contributing to the light absorbing property of HULIS and it was also the most DTT-active; while HULIS from secondary processes were the least DTT-active. [ABSTRACT FROM AUTHOR]

Water-soluble organic nitrogen (WSON) is ubiquitous in fine particulate matter (PM 2.5) and poses health and environmental risks. However, there is limited knowledge regarding its comprehensive speciation and source-specific contributions. Here, we conducted chemical characterization and source apportionment of WSON in 65 PM 2.5 samples collected in Hong Kong during a 1-yr period. Using various mass-spectrometry-based techniques, we quantified 22 nitrogen-containing organic compounds (NOCs), including 17 nitroaromatics (NACs), four amines, and urea. The most abundant amine and NACs were dimethylamine and 4-nitrocatechol, respectively. Two secondary (i.e., secondary formation and secondary nitrate) and five primary sources (i.e., sea salt, fugitive dust, marine vessels, vehicle exhaust, and biomass burning) of WSON and these three categories of NOCs were identified. Throughout the year, secondary sources dominated WSON formation (69.0%), while primary emissions had significant contributions to NACs (77.1%), amines (75.9%), and urea (83.7%). Fugitive dust was the leading source of amines and urea, while biomass burning was the main source of NACs. Our multi-linear regression analysis revealed the significant role of sulfate, NO 3 , nitrate, liquid water content, and particle pH on WSON formation, highlighting the importance of nighttime NO 3 processing and heterogeneous and aqueous-phase formation of NOCs in the Hong Kong atmosphere. [Display omitted] • Aerosol phase WSON is mainly secondarily formed (69.0%) in Hong Kong. • Heterogeneous and aqueous-phase reactions and nighttime NO 3 oxidation are major formation pathways of WSON. • Sulfate and NO 3 played key roles in WSON formation. • Nitroaromatic compounds were predominantly from biomass-burning. • Amines and urea were primarily from dust and crustal origin. [ABSTRACT FROM AUTHOR]

Increasing scientific findings show that the adverse health effects of PM 2.5 are related not only to its mass but also PM 2.5 sources and chemical compositions. Here, we conducted a comprehensive characterization and source apportionment of oxidative potential (OP) of water-soluble PM 2.5 collected in Hong Kong for one year. Two OP indicators, namely dithiothreitol (DTT) consumption and ∙OH formation, were quantified. Six PM 2.5 sources, i.e. secondary sulfate, biomass burning, secondary organic aerosol (SOA), vehicle emissions, marine vessels, and a metal-related factor, were apportioned and identified to be DTT active. The four primary sources accounted for 83.5% of DTT activity of water-soluble PM 2.5 , with the metal-related factor and marine vessels as the leading contributors. However, only three sources, i.e. metal-related factor, vehicle emissions, and SOA, showed ∙OH generation ability, with a predominant contribution of 96.2% from the two primary sources, especially the metal-related factor (84.5%). Based on the source apportionment results, we further evaluate the intrinsic OP of water-soluble PM 2.5 from each source. Marine vessels exhibited the highest intrinsic DTT activity; while metal-related factor was most effective in ∙OH generation. ga1 • Primary sources accounted for 83.5% of DTT activity induced by water-soluble PM 2.5. • Primary sources contributed 96.2% of ∙OH generation induced by water-soluble PM 2.5. • The metal-related source was the leading contributor to both DTT and ∙OH activities. • Water-soluble PM 2.5 from marine vessels exhibited the highest intrinsic DTT activity. • The metal-related factor was most effective in ∙OH generation. [ABSTRACT FROM AUTHOR]