Di Hu

Contributions of isoprene, monoterpenes, β‐caryophyllene, and toluene to secondary organic aerosols in Hong Kong during the summer of 2006

[1]xa0Isoprene, monoterpenes, β-caryophyllene, and toluene are known to be important secondary organic aerosol (SOA) precursors. In this study, characteristic SOA tracers of these precursors were quantified in ambient samples of PM2.5 taken in Hong Kong and their contributions to SOA were estimated using a tracer-based method. Samples were collected every other day from four sampling sites during a field measurement campaign in the summer of 2006. Fourteen SOA tracers, along with 24 other polar oxygenated compounds, were identified and quantified using gas chromatography/ion trap mass spectrometry with prior trimethylsilylation. Concentrations of the individual tracers ranged from a few tenths to a few hundreds ng m−3. The tracer concentrations were found to be 1 order of magnitude higher on days under regional transport influences due to elevated oxidant levels than on days under mainly local emissions influences. Using the measured SOA tracer concentrations in the ambient aerosols and laboratory-derived tracer mass fractions reported by Kleindienst et al. (2007), we estimated that the average SOA attributable to isoprene, monoterpenes, β-caryophyllene, and toluene was 8.83 μg m−3 on days under regional transport influences versus 0.99 μg m−3 on days under mainly local emissions influences, accounting for approximately 49% and 21%, respectively, of the ambient OC concentrations. The tracer-based estimates indicate that monoterpenes and β-caryophyllene are significant contributors to ambient PM2.5 in the summer, which may be due to the high emissions of these biogenic hydrocarbons in Hong Kong.

Sources, transformation, and health implications of PAHs and their nitrated, hydroxylated, and oxygenated derivatives in PM2.5 in Beijing

Fine particulate matter (PM2.5) is a significant health issue in Chinese megacities. However, little information is available regarding the PM2.5-bound toxic organics, especially their sources, atmospheric transformations, and health implications. In this study, we assessed the levels of polycyclic aromatic hydrocarbons (PAHs) and their nitrated, hydroxylated, and oxygenated derivatives (i.e., NPAHs, OHPAHs, and OPAHs, respectively) in PM2.5 collected in Beijing over a one-year period. The median concentration of 23 PAHs, 15 NPAHs, 16 OHPAHs, and 7 OPAHs in PM2.5 was 53.8, 1.14, 1.40, and 3.62 ng m−3, respectively. Much higher concentrations and mass percentages for all species were observed in the heating season, indicating a higher toxicity of PM2.5 during this period of time. Positive matrix factorization (PMF) was applied to apportion the sources of PAHs and their derivatives. It was found that traffic emissions in the non-heating season, and coal combustion and biomass burning in the heating season, were the major primary sources of PAHs and their derivatives. Secondary formation, however, contributed significantly to the derivatives of PAHs (especially NPAHs and OPAHs) in the non-heating season, suggesting significant impacts of atmospheric transformation on the toxicity of PM2.5.

Source apportioning of primary and secondary organic carbon in summer PM2.5 in Hong Kong using positive matrix factorization of secondary and primary organic tracer data

[1]xa0The major inorganic constituents and organic tracer compounds in PM2.5 were used in positive matrix factorization (PMF) and chemical mass balance (CMB) models to apportion the primary and secondary source contributions to organic carbon (OC) in Hong Kong during the summer of 2006. Secondary organic aerosol (SOA) tracers of several biogenic and anthropogenic hydrocarbons were included in the PMF analysis. Their inclusion allowed the identification of two components of SOA among seven factors resolved by PMF. One SOA component was mainly associated with secondary sulfate and nitrate. The other SOA component, characterized by biogenic SOA tracers and mixed with biomass burning and vegetative detritus particles, was biomass burning-induced SOA. Secondary OC (SOC) apportioned by PMF (SOCPMF) was on average 6.84 μgC m−3 (65% of PM2.5 OC) on high pollution days under influence of significant regional transport (i.e., regional days) and 0.70 μgC m−3 (25% of PM2.5 OC) on days under the influence of mainly local emissions (i.e., local days). The biomass burning-induced SOA accounted for 20% of the total SOA on the regional days, underlining the importance of biomass burning aerosol source in this region. The average uncertainty for the SOCPMF estimates was ∼20% on the regional days and ∼120% on the local days. SOCPMF was compared with SOC determined by CMB (SOCCMB, i.e., unapportioned OC by CMB analysis) and a tracer-based method (SOCTBM) that apportioned SOC contributions by four hydrocarbon precursors including isoprene, monoterpenes, β-caryophyllene, and toluene. The three estimates of SOC closely tracked with each other among individual samples. The SOCCMB and SOCPMF estimates on the majority of the regional days differed from each other by less than 25%. Good correlations between contributions of SOC and individual primary OC sources apportioned by PMF and CMB further added to the credence to the PMF-derived estimation of secondary and primary OC source contributions by using secondary and primary aerosol organic tracers as the fitting species.

A quantitative assessment of source contributions to fine particulate matter (PM2.5)-bound polycyclic aromatic hydrocarbons (PAHs) and their nitrated and hydroxylated derivatives in Hong Kong

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 (PM2.5) in Hong Kong are still lacking. In this study, we conducted a 1-year observation at an urban site in Hong Kong. PM2.5-bound PAHs and their derivatives were measured, with median concentrations of 4590, 44.4 and 31.6xa0pgxa0m-3 for ∑21PAHs, ∑13NPAHs, and ∑12OHPAHs, 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 PM2.5 toxicity, the mixed source of coal combustion and NPAHs secondary formation was the major contributor, followed by biomass burning and vehicle emissions.

Characterization of Chemical Components and Bioreactivity of Fine Particulate Matter (PM2.5) during Incense Burning

The chemical and bioreactivity properties of fine particulate matter (PM2.5) emitted during controlled burning of different brands of incense were characterized. Incenses marketed as being environmentally friendly emitted lower mass of PM2.5 particulates than did traditional incenses. However, the environmentally friendly incenses produced higher total concentrations of non-volatile polycyclic aromatic hydrocarbons (PAHs) and some oxygenated polycyclic aromatic hydrocarbons (OPAHs). Human alveolar epithelial A549xa0cells were exposed to the collected PM2.5, followed by determining oxidative stress and inflammation. There was moderate to strong positive correlation (Rxa0>xa00.60, pxa0<xa00.05) between selected PAHs and OPAHs against oxidative-inflammatory responses. Strong positive correlation was observed between interleukin 6 (IL-6) and summation of total Group B2 PAHs/OPAHs (∑7PAHs/ΣOPAHs). The experimental data indicate that emissions from the environmentally friendly incenses contained higher concentrations of several PAH and OPAH compounds than did traditional incense. Moreover, these PAHs and OPAHs were strongly correlated with inflammatory responses. The findings suggest a need to revise existing regulation of such products.

Secondary organic aerosol tracers and malic acid in Hong Kong: Seasonal trends and origins

Environmental context Secondary organic aerosols (SOAs), a major organic component of ambient fine particles, contribute to adverse health effects and visibility degradation. Quantification of SOA tracers allows estimation of contributions from specific precursors, which helps the formulation of effective control strategies. We found that malic acid was present in SOA at high abundance in both winter and summer; its seasonally distinct inter-species relationships offer insights into distinct SOA formation pathways. Abstract Fine particle samples collected at an urban location in Hong Kong during winter were analysed by gas chromatography–ion trap mass spectrometry with prior chemical derivatisation. In total, 15 secondary organic aerosol (SOA) tracers from isoprene, monoterpenes, β-caryophyllene and toluene, and 24 other polar oxygenated compounds, were identified and quantified. Monoterpenes and isoprene SOA tracers showed lower levels on winter long-range transport (LRT) days than summer regional days, the latter being reported in our previous study. Opposite seasonal trends were observed for SOA tracers of β-caryophyllene and toluene. The averaged total secondary organic carbon (SOC) apportioned to these four volatile organic compounds (VOCs) was estimated to be 4.73μgCm–3 on winter LRT days, lower than that on summer regional days (5.21μgCm–3). β-caryophyllene and monoterpenes were found to be the most significant SOC contributors to PM2.5 in Hong Kong in both winter and summer, and their averaged SOC contributions on winter LRT days were 2.24 and 1.59μgCm–3. Toluene and isoprene had relatively minor contributions to SOC in Hong Kong in both seasons, with averaged SOC contributions of 0.81 and 0.08μgCm–3 on winter LRT days. Malic acid was well correlated with biogenic SOA tracers and oxalate in both seasons, whereas correlation between malic and succinic acid was only found in winter. Based on the seasonal characteristic inter-species correlations in the region, we hypothesise that malic acid could be formed mainly by the aqueous-phase photodegradation of SOA products of biogenic VOCs during summer. In winter, emissions of biogenic VOCs are greatly reduced and succinic acid then becomes the predominant contributor to malic acid.

Development and application of a quantification method for water soluble organosulfates in atmospheric aerosols

In recent years, organosulfates have been found as a significant component of secondary organic aerosols from both smog chamber experiments and field measurements. In this study, an indirect method was developed to estimate organosulfates in aerosol particles as a whole based on their sulfate functional group. A series of experiments were conducted to optimize and validate the method, and it was then applied to quantify organosulfates in the aerosol samples collected at three sampling characteristic sites in Shenzhen, with one close to a power plant (PP), one at a heavy traffic intersection (HTI), and one on the campus of Harbin Institute of Technology Shenzhen graduate school (HITSZ). On average, the mass concentrations of organic sulfur (Sorg) were 1.98, 1.11, 0.25xa0μgS m-3 in PP, HTI and HITSZ respectively. The lower bounds of mass concentrations of organosuflates (OMs-related) were 6.86, 3.85 and 0.86xa0μgxa0m-3 and the upper bounds of mass concentrations of organosulfates were 23.05, 12.93 and 2.90xa0μgxa0m-3 in PP, HTI and HITSZ respectively. This indicates that primary emissions from coal burning and automobile exhaust can promote the secondary formation of organosulfates in the atmosphere. Overall, the mass concentrations observed in this work were higher than those reported by previous studies.