Chemical characteristics of road dust PM2.5 fraction in oasis cities at the margin of Tarim Basin

In order to understand the compositions characteristics of particulate matter with aerodynamic diameter less than 2.5μm(PM2.5)fraction in road dust(RD2.5)of oasis cities on the edge of Tarim Basin,30 road dust(RD)samples were collected in Kashi,Cele,and Yutian in the spring,2018,and RD2.5 was collected using the resuspension approach.Eight watersoluble ions,39 trace elements and 8 fractions of carbon-containing species in PM2.5 were analyzed.Ca2+and Ca were the most abundant ions and elements in RD2.5(7.1%and 9.5%).Cl-in RD2.5 was affected not only by attributed to saline-alkali soils in oasis cities of the Tarim Basin and dust from Taklimakan Desert but also by human activities.Moreover,the organic carbon/elemental carbon(OC/EC)ratio indicated that carbon components in RD2.5in Cele town mainly come from fossil fuel combustion,while those in Yutian and Kashi mainly come from biomass combustion.It is noteworthy that high Ca in RD2.5 was seriously affected by anthropogenic emissions,and high Na and K contents in RD2.5 could be derived from soil and desert dust.It was estimated that Cd,Tl,Sn and Cr were emitted from anthropogenic emissions using the enrichment factor.The coefficients of divergence(cOD)result indicated that the influence of local emission on road dust emission is greater than that of long-distance transmission.This study is the first time to comprehensively analyze the chemical characteristics of road dust in oasis cities,and the results provides the sources of road dust at the margin of Tarim Basin.

Vertical distribution of volatile organic compounds conducted by tethered balloon in the Beijing-Tianjin-Hebei region of China

Volatile organic compounds(VOCs) as precursors of ozone and secondary organic aerosols can cause adverse effects on the environment and human health.However,knowledge of the VOC vertical profile in the lower troposphere of major Chinese cities is poorly understood.In this study,tethered balloon flights were conducted over the juncture of BeijingTianjin-Hebei in China during the winter of 2016.Thirty-six vertical air samples were collected on selected heavy and light pollution days at altitudes of 50-1000 meters above ground level.On average,the concentration of total VOCs(TVOCs) at 50-100 m was 4.9 times higher than at 900-1000 m(46.9 ppbV vs.8.0 ppbV).TVOC concentrations changed rapidly from altitudes of 50-100 to 401-500 m,with an average decrease of 72%.With further altitude increase,the TVOC concentration gradually decreased.The xylene/benzene ratios of 34/36 air samples were lower than 1.1,and the benzene/toluene ratios of 34/36 samples were higher than 0.4,indicating the occurrence of aged air mass during the sampling period.Alkenes contributed most in terms of both OH loss rate(39%-71%) and ozone formation potential(40%-72%),followed by aromatics(6%-38%).Finally,the main factors affecting the vertical distributions of VOCs were local source emission and negative dispersion conditions on polluted days.These data could advance our scientific understanding of VOC vertical distribution.

Emission factors of polycyclic aromatic hydrocarbons from domestic coal combustion in China

Domestic coal stove is widely used in China, especially for countryside during heating period of winter, and polycyclic aromatic hydrocarbons （PAHs） are important in flue gas of the stove. By using dilution tunnel system, samples of both gaseous and particulate phases from domestic coal combustion were collected and 18 PAH species were analyzed by GC-MS. The average emission factors of total 18 PAH species was 171.73 mg/kg, ranging from 140.75 to 229.11 mg/kg for bituminous coals, while was 93.98 mg/kg, ranging from 58.48 to 129.47 mg/kg for anthracite coals. PAHs in gaseous phases occupied 95% of the total of PAHs emission of coal combustion. In particulate phase, 3-ring and 4- ring PAHs were the main components, accounting for 80% of the total particulate PAHs. The total toxicity potency evaluated by benzo[a]pyrene-equivalent carcinogenic power, sum of 7 carcinogenic PAH components and 2,3,7,8-tetrachlorodibenzodioxin had a similar tendency. And as a result, the toxic potential of bituminous coal was higher than that of anthracite coal. Efficient emission control should be conducted to reduce PAH emissions in order to protect ecosystem and human health.

Theoretical study on the reaction mechanism of ozone addition to the double bonds of keto-limonene

The reaction mechanism of ozone （O 3） addition to the double bonds of gas phase keto-limonene was investigated using ab initio methods.Two different possibilities for O 3 addition to the double bond were considered and two corresponding van der Waals complexes （Complex 1 and Complex 2） were found for 1-endo and 2-endo.The rate constants were calculated using the transition state theory at the CCSD（T）/6-31G（d）＋ CF//B3LYP/6-31G（d,p） level.The high-pressure limit of the total rate constant at 298 K was 3.51×10-16 cm 3/（molecule·sec）,which was in a good agreement with the experimental data.