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[1] In order to investigate the optical properties of atmospheric aerosol in the urban area of Beijing, in situ and remote measurements of particulate pollutants were conducted at an urban site ( , respectively. Average mass scattering efficiency of PM 10 and PM 2.5 particle were found to be 2.5 ± 1.1 and 3.4 ± 1.2 m 2 g À1 , respectively. Average single scattering albedo (SSA) of dry PM 10 was characterized to be 0.82 ± 0.09. It was found that SSA decreased to lower values of $0.75 during the relatively clean condition while it increased up to $0.86 during polluted condition mainly owing to the increases of ammonium sulfate, ammonium nitrate, and organic mass by carbon's contributions to PM mass concentrations. Pollution episodes in Beijing were strongly related to wind speed and wind direction. Stagnant weather conditions with southerly wind and low wind speed accelerated the accumulation of the pollutants in Beijing, which led to severe haze. It has been found that high PM 2.5 /AOT (aerosol optical thickness) ratio of 228.2 mg m À3 was observed when air mass was transported from western or northern China while significantly lower PM 2.5 /AOT of 107.6 mg m À3 was observed when it was affected mostly by local air pollutants in Beijing.

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Ultraperformance convergence chromatography/tandem triple quadrupole mass spectrometry (UPC(2)-MS/MS) is a novel tool in separation science that combines the advantages of supercritical fluid chromatography with ultraperformance liquid chromatography/MS/MS technology. The use of nontoxic CO2 fluid and a postcolumn additive to complement MS/MS allows better control of analyte retention for chiral separation and high-sensitivity determination with different chiral stationary phases. This paper reports the stereoselective separation and determination of the chiral neonicotinoid sulfoxaflor in vegetables and soil by UPC(2)-MS/MS. Baseline resolution (Rs ≥ 1.56) of and high selectivity (LOQ ≤ 1.83 μg/kg) for the four stereoisomers were achieved by postcolumn addition of 1 % formic acid-methanol to a Chiralpak IA-3 using CO₂/isopropanol/acetonitrile as the mobile phase at 40 °C, 2,500 psi, and for 6.5 min in electrospray ionization positive mode. Rearranged Van't Hoff equations afforded the thermodynamic parameters ΔH (ο) and ΔS (ο), which were analyzed to promote understanding of the enthalpy-driven separation of sulfoxaflor stereoisomers. The interday mean recovery, intraday repeatability, and interday reproducibility varied from 72.9 to 103.7%, from 1.8 to 9.2%, and from 3.1 to 9.4%, respectively. The proposed method was used to study the pharmacokinetic dissipation of sulfoxaflor stereoisomers in soil under greenhouse conditions. The estimated half-life ranged from 5.59 to 6.03 d, and statistically nonsignificant enantioselective degradation was observed. This study not only demonstrates that the UPC(2)-MS/MS system is an efficient and sensitive method for sulfoxaflor stereoseparation, but also provides the first experimental evidence of the pharmacokinetic dissipation of sulfoxaflor stereoisomers in the environment.

Aerosol optical properties were measured in Beijing in summer and winter using a state‐of‐the‐art cavity attenuated phase shift single scattering albedo monitor (CAPS PMssa) along with aerosol composition measurements by aerosol mass spectrometers and aethalometers. The SSA directly measured by the CAPS PMssa showed overall agreements with those derived from colocated measurements. However, substantial differences were observed during periods with low SSA values in both summer and winter, suggesting that interpretation of low SSA values needs to be cautious. The average (±σ) extinction coefficient (bext) and absorption coefficient (bap) were 336 (±343) Mm−1 and 44 (±41) Mm−1, respectively, during wintertime, which were approximately twice those observed in summer, while the average SSA was relatively similar, 0.86 (±0.06) and 0.85 (±0.04) in summer and winter, respectively. Further analysis showed that the variations in SSA can be approximately parameterized as a function of mass fraction of secondary particulate matter (fSPM), which is SSA = 0.74 + 0.19 × fSPM (fSPM > 0.3, r2 = 0.85). The contributions of aerosol species to extinction coefficients during the two seasons were also estimated. Our results showed that the light extinction was dominantly contributed by ammonium sulfate (30%) and secondary organic aerosol (22%) in summer, while organic aerosol was the largest contributor (51%) in winter. Consistently, SPM played the major role in visibility degradation in both seasons by contributing 70% of the total extinction.

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