Li

Diurnal variations of polycyclic aromatic hydrocarbons associated with PM2.5 in Shanghai, China

Forty-eight daily time interval PM2.5 samples were collected from December 2006 to January 2008 in an urban site in Shanghai, China. Concentrations and compositions of polycyclic aromatic hydrocarbons (PAHs) were analyzed with GC-MS to study the diurnal and seasonal variations and to identify the main emitting sources. The diurnal variation of the PAHs concentrations was greater in the late autumn and winter sampling days, and was greatly influenced by meteorological conditions such as wind speed and ambient temperature. The concentration of PAHs in the mornings (6:30-10:00) increased distinctly, and was high in the late autumn and winter sampling days, indicating the contribution from vehicle emissions during rush hours. The diurnal variation of the high molecular weight PAHs did not seem to be controlled by the shift of gas-particle partitioning due to temperature variation, instead, it could be indicative of the variation in the source. Statistical analyses showed that the concentrations of PAHs were negatively correlated with temperature and wind speed, and positively correlated with relative humidity. Diagnostic ratios of PAHs suggested mixed emission sources of petroleum and coal/biomass combustion for PAHs in the PM2.5 in Shanghai.

Composition, source, mass closure of PM2.5 aerosols for four forests in eastern China.

PM2.5 aerosols were collected in forests along north latitude in boreal-temperate, temperate, subtropical and tropical climatic zones in eastern China, i.e., Changbai Mountain Nature Reserve (CB), Dongping National Forest Park in Chongming Island (CM), Dinghu Mountain Nature Reserve (DH), Jianfengling Nature Reserve in Hainan Island (HN). The mass concentrations of PM2.5, organic carbon (OC), elemental carbon (EC), water soluble organic carbon (WSOC) as well as concentrations of ten inorganic ions (F-, Cl-, NO3-, SO4(2-), C2O4(2-), NH4+, Na+, K+, Ca2+, Mg2+) were determined. Aerosol chemical mass closures were achieved. The 24-hr average concentrations of PM2.5 were 38.8, 89.2, 30.4, 18 Cig/m3 at CB, CM, DH and HN, respectively. Organic matter and EC accounted for 21%-33% and 1.3%-2.3% of PM2.5 mass, respectively. The sum of three dominant secondary ions (SO4(2-), NO3-, NH4+) accounted for 44%, 50%, 45% and 16% of local PM2.5 mass at CB, CM, DH and HN, respectively. WSOC comprised 35%-65% of OC. The sources of PM2.5 include especially important regional anthropogenic pollutions at Chinese forest areas.

Ozone sensitivity analysis with the MM5-CMAQ modeling system for Shanghai.

Ozone has become one of the most important air pollution issues around the world. This article applied both O3/(NO(y)-NO(x)) and H2O2/HNO3 indicators to analyze the ozone sensitivity in urban and rural areas of Shanghai, with implementation of the MM5-CMAQ modeling system in July, 2007. The meteorological parameters were obtained by using the MM5 model. A regional emission inventory with spatial and temporal allocation based on the statistical data has been developed to provide input emission data to the MM5-CMAQ modeling system. Results showed that the ozone concentrations in Shanghai show clear regional differences. The ozone concentration in rural areas was much higher than that in the urban area. Two indicators showed that ozone was more sensitive to VOCs in urban areas, while it tended to be NO(x) sensitive in rural areas of Shanghai.

Chemical characteristics of fine particles and their impact on visibility impairment in Shanghai based on a 1-year period observation.

In this work, a one-year observation focusing on high time resolution characteristics of components in fine particles was conducted at an urban site in Shanghai. Contributions of different components on visibility impairment were also studied. Our research indicates that the major components of PM2.5 in Shanghai are water-soluble inorganic ions and carbonaceous aerosol, accounting for about 60% and 30% respectively. Higher concentrations of sulfate (SO42-) and organic carbon (OC) in PM2.5 occurred in fall and summer, while higher concentrations of nitrate (NO3-) were observed in winter and spring. The mass concentrations of Cl- and K+ were higher in winter. Moreover, NO3- increased significantly during PM2.5 pollution episodes. The high values observed for the sulfate oxidizing rate (SOR), nitrate oxidizing rate (NOR) and secondary organic carbon (SOC) in OC indicate that photochemical reactions were quite active in Shanghai. The IMPROVE (Interagency Monitoring of Protected Visual Environments) formula was used in this study to investigate the contributions of individual PM2.5 chemical components to the light extinction efficient in Shanghai. Both NH4NO3 and (NH4)2SO4 had close relationships with visibility impairment in Shanghai. Our results show that the reduction of anthropogenic SO2, NOx and NH3 would have a significant effect on the improvement of air quality and visibility in Shanghai.

Development of a Compound-Specific Carbon Isotope Analysis Method for 2-Methyltetrols, Biomarkers for Secondary Organic Aerosols from Atmospheric Isoprene

The stable carbon isotope compositions of 2-methyltetrols, biomarker compounds for secondary organic aerosols formed from isoprene in the atmosphere, have been determined by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). In this work, isoprene with various delta(13)C values was used to produce 2-methyltetrols via an oxidation reaction with hydrogen peroxide in sulfuric acid under direct sunlight. The target compounds with different stable carbon isotope compositions were then derivatized by methylboronic acid with a known delta(13)C value and measured by GC/C/IRMS. With delta(13)C values of 2-methyltetrols and methylboronic acid predetermined, isotopic fractionation is evaluated for the derivatization process. Through reduplicate delta(13)C measurements, the carbon isotope analysis achieved excellent reproducibility and high accuracy with an average error of <0.3 per thousand. The differences between the predicted and measured delta(13)C values range from -0.10 to 0.29 per thousand, indicating that the derivatization process does not introduce isotopic fractionation. The delta(13)C values of 2-methyltetrols could be calculated on the basis of the stoichiometric mass balance equation among 2-methyltetrols, methylboronic acid, and methylboronate derivatives. Preliminary tests of 2-methyltetrols in PM(2.5) aerosols at two forested sites were conducted and revealed significant differences in their isotope compositions, implying possible application of the method in helping us understand the primary emission, photochemical reaction, or removal processes of isoprene in the atmosphere.

Determination of the stable carbon isotopic compositions of 2‐methyltetrols in ambient aerosols from the Changbai Mountains

Isoprene is one of the most important non-methane hydrocarbons (NMHCs) in the troposphere: it is a significant precursor of O(3) and it affects the oxidative state of the atmosphere. The diastereoisomeric 2-methyltetrols, 2-methylthreitol and 2-methylerythritol, are marker compounds of the photooxidation products of atmospheric isoprene. In order to obtain valuable information on the delta(13)C value of isoprene in the atmosphere, the stable carbon isotopic compositions of the 2-methyltetrols in ambient aerosols were investigated. The 2-methyltetrols were extracted from filter samples and derivatized with methylboronic acid, and the delta(13)C values of the methylboronate derivatives were determined by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). The delta(13)C values of the 2-methyltetrols were then calculated through a simple mass balance equation between the 2-methyltetrols, methylboronic acid and the methylboronates. The delta(13)C values of the 2-methyltetrols in aerosol samples collected at the Changbai Mountain Nature Reserves in eastern China were found to be -24.66 +/- 0.90 per thousand and -24.53 +/- 1.08 per thousand for 2-methylerythritol and 2-methylthreitol, respectively. Based on the measured isotopic composition of the 2-methyltetrols, the average delta(13)C value of atmospheric isoprene is inferred to be close to or slightly heavier than -24.66 per thousand at the collection site during the sampling period.

Gas chromatography/combustion/isotope ratio mass spectrometric analysis of the stable carbon composition of tetrols

The stable carbon isotope compositions of tetrols, erythritol and threitol were determined by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). Using four tetrols with various delta(13)C values derivatized by methylboronic acid, the carbon isotope analysis method achieved excellent reproducibility and high accuracy. There was no carbon isotopic fractionation during the derivatization processes. The differences in the carbon isotopic compositions of methylboronates between the measured and calculated ranged from -0.20 to 0.12 per thousand, within the specification of the GC/C/IRMS system. It was demonstrated that delta(13)C values of tetrols could be calculated by a simple mass balance equation between tetrols, methylboronic acid, and methylboronates. The analogous 2-methyltetrols, marker compounds of photooxidation products of atmospheric isoprene, should have similar behavior using the same derivatization reagent. This method may provide insight on sources and sinks of atmospheric isoprene.

The Particle-Phase Polycyclic Aromatic Hydrocarbons Exhausted from Diesel Engines Fuelled with Emulsified Diesel

Emulsified diesel is an alternative fuel for internal combustion engines. It can reduce the emitted pollutants. In this work, the effect of water-oil emulsions on the particulate matter (PM) and particle-phase polycyclic aromatic hydrocarbons (PAH) composition exhausted by diesel engine was studied. Three different water-oil blends emulsions with volume fractions of water ranging from 0% to 15% were investigated. The experimental results indicated that the mean reductions of PM mass concentration of E10, E15 are 19.31% and 17.99%, respectively, compared with E0.The mean increases of total PAH content of E10, E15 are 5.08% and 20.19%, respectively, compared with E0. The BaPeq (benzo [a] pyrene equivalent toxicity) of E0, E10 and E15 are 4.75, 6.53 and 8.86 respectively. Therefore, the blending fraction is a significant factor for the particle-phase total PAH content. Besides, researches on health effects of emulsified diesel are needed as well.

Ammonia Emission Measurements for Light-Duty Gasoline Vehicles in China and Implications for Emission Modeling

Motor vehicle ammonia (NH3) emissions have attracted increasing attention for their potential to form secondary aerosols in urban atmospheres. However, vehicle NH3 emission factors (EFs) remain largely unknown due to a lack of measurements. Thus, we conducted detailed measurements of NH3 emissions from 18 Euro 2 to Euro 5 light-duty gasoline vehicles (LDGVs) in Shanghai, China. The distance- and fuel-based NH3 EFs average 29.2 ± 24.1 mg·km-1 and 0.49 ± 0.41 g·kg-1, respectively. The average NH3-to-CO2 ratio is 0.41 ± 0.34 ppbv·ppmv-1. The measurements reveal that NH3 emissions from LDGVs are strongly correlated with both vehicle specific power (VSP) and the modified combustion efficiency (MCE); these relationships were used to predict LDGV NH3 EFs via a newly developed model. The predicted LDGV NH3 EFs under urban and highway driving cycles are 23.3 mg·km-1 and 84.5 mg·km-1, respectively, which are consistent with field measurements. The NH3 EF has decreased by 32% in average since the implementation of vehicle emission control policies in China five years ago. The model presented herein more accurately predicts LDGV NH3 emissions, contributing substantially to the compilation of NH3 emission inventories and prediction of future motor vehicle emissions in China.

Intermediate Volatility Organic Compound Emissions from a Large Cargo Vessel Operated under Real-world Conditions

Intermediate volatility organic compound (IVOC) emissions from a large cargo vessel were characterized under real-world operating conditions using an on-board measurement system. Test ship fuel-based emission factors (EFs) of total IVOCs were determined for two fuel types and seven operating conditions. The average total IVOC EF was 1003 ± 581 mg·kg-fuel-1, approximately 0.76 and 0.29 times the EFs of primary organic aerosol (POA) emissions from low-sulfur fuel (LSF, 0.38 wt % S) and high-sulfur fuel (HSF, 1.12 wt % S), respectively. The average total IVOC EF from LSF was 2.4 times that from HSF. The average IVOC EF under low engine load (15%) was 0.5-1.6 times higher than those under 36%-74% loads. An unresolved complex mixture (UCM) contributed 86.1 ± 1.9% of the total IVOC emissions. Ship secondary organic aerosol (SOA) production was estimated to be 546.5 ± 284.1 mg·kg-fuel-1; IVOCs contributed 98.9 ± 0.9% of the produced SOA on average. Fuel type was the dominant determinant of ship IVOC emissions, IVOC volatility distributions, and SOA production. The ship emitted more IVOC mass, produced higher proportions of volatile organic components, and produced more SOA mass when fueled with LSF than when fueled with HSF. When reducing ship POA emissions, more attention should be paid to commensurate control of ship SOA formation potential.