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Start Over Author "Qijing Bian" Journal aerosol and air quality research
2 results on '"Qijing Bian"'

1. Observation of Vapor Wall Deposition in a Smog Chamber Using Size Evolution of Pure Organic Particles

Author

Vikram Pratap, S. Aditya Kiran, Qijing Bian, Jeffrey R. Pierce, Philip K. Hopke, and Shunsuke Nakao

Subjects
Organic aerosol, Teflon chamber, Vapor wall loss, Levoglucosan, Low temperature, Science
Abstract

Abstract Prior studies have shown that neglecting the vapor wall loss could lead to the underestimation of the secondary organic aerosol (SOA) yields in smog chamber experiments. The majority of the previous studies investigated vapor wall loss of a wide range of semi-volatile organic vapors at room temperatures using extensive chemical analysis. This study poses a question: Can vapor wall deposition in a smog chamber be observed only using physical measurements of aerosol properties? This study assesses the significance of vapor wall loss using only the size evolution of pure organic compound particles. To our knowledge, this technique is used for the first time in assessing the vapor wall loss of chemical species in chamber experiments. Dark experiments were conducted by injecting pure levoglucosan particles into an outdoor smog chamber at multiple ambient temperatures, ranging from −10°C to +15°C. Peak diameter analysis revealed levoglucosan particles shrunk by ~37% at 15°C and ~20% at 10°C experiments, whereas no shrinkage was observed at temperatures below 0°C suggesting significant vapor wall loss of levoglucosan at warmer temperatures (> 10°C). Two-Moment Aerosol Sectional (TOMAS) and additional simple kinetic model simulations suggest that the effects of temperature on vapor wall loss can primarily be explained by the change in saturation vapor pressure of the organic compound and that the lack of apparent vapor wall loss of levoglucosan below 0°C was due to kinetics, i.e., slow evaporation relative to the chamber experiment timescales. The same approach can be applied to other organic species to expand the range of volatility relevant to chamber experiments.

Published
2020
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2. Characterization of PM2.5 Major Components and Source Investigation in Suburban Hong Kong: A One Year Monitoring Study

Author

Jian Zhen Yu, Peter K.K. Louie, Wai Man Ng, X. H. Hilda Huang, and Qijing Bian

Subjects
chemistry.chemical_classification, Total organic carbon, Ammonium sulfate, Ammonium nitrate, complex mixtures, Pollution, chemistry.chemical_compound, chemistry, Nitrate, Environmental chemistry, Environmental Chemistry, Ammonium, Organic matter, Sulfate, Air quality index
Abstract

PM2.5 filter sampling was conducted on a daily basis at the HKUST Air Quality Research Supersite (AQRS) for one year from March 2011 to February 2012. Approximately one fifth of the filter samples were subjected to full chemical analysis including major ions, elements, organic carbon (OC), elemental carbon (EC), and non-polar organic compounds (NPOCs). The major ions (sulfate, nitrate, and ammonium) were compared with those measured online by a MARGA system and the two sets of data were found in agreement within 25% or better. The major PM2.5 components (crustal materials, organic matter, soot, ammonium sulfate, ammonium nitrate, and non-crustal trace elements) accounted for 90% of the measured mass with sulfate being the most abundant (32.0%), followed by organic matter (23.5%) and ammonium (11.8%). The monthly variation patterns for different components suggested variable regional/super-regional sources, reflecting variation of transport contribution caused by shifts in synoptic weather conditions. Receptor modeling analysis by Positive Matrix Factorization revealed that secondary sulfate formation process (annual average of 31%), biomass burning (23%), and secondary nitrate formation process (13%) were the three dominant contributing sources to the observed PM2.5 at HKUST AQRS throughout the sampling year. The PM2.5 mass concentrations of all the individual sampling days were within the recently-proposed AQOs standards by the Hong Kong government (35 µg/m 3 for annual average and 75 µg/m 3 for 24-hr average) while approx. 52% of the sampling days were recorded with PM2.5 concentrations exceeding the WHO health 24-hr standards of 25 µg/m 3 . Major composition and source analysis showed that the increased mass concentrations on high PM days were mainly caused by air pollutant transport from the outside-Hong Kong regions. Results from this study indicate the importance of regional/super-regional strategies such as reduction in SO2, NO2 (precursors for secondary inorganic aerosols) and restricting biomass burning for lowering PM2.5 in Hong Kong.

Published
2014
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