AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Hygroscopic Growth Measurements of Ambient Aerosol at a Suburban Site in Hong Kong: Seasonal Trends and Water-Uptake Behavior as a Function of Relative Humidity
Ming Chee Yeung, CHAK K. CHAN, Hong Kong University of Science and Technology
Abstract Number: 275 Working Group: Aerosols, Clouds, and Climate
Abstract Rapid economic growth and industrialization in the Pearl River Delta (PRD) region of South-Eastern China in the past decades have led to poor air quality in this region. Most of the previous aerosol studies in this region focused on the characterization of chemical composition. However, measurements of hygroscopic properties, which are crucial to a proper description of aerosol climate effect, are scarce.
In the work, we conducted real-time hygroscopic growth measurements using a BMI Humidified-Tandem Differential Mobility Analyzer at a suburban site in Hong Kong of the PRD region starting May 2011. The particle diameter growth factors (GF) at 90% relative humidity (RH) were measured for dry particle diameters between 35 and 250 nm, covering a month in each of the four seasons for investigating the seasonal variations.
The GFs were generally similar with occasional variations over the study periods. Lower GFs (1.4 to 1.6) of the Aitken mode (dry diameter = 35 to 75 nm) than those of the accumulation mode (dry diameter = 100 to 250 nm, GF = 1.5 to 1.7) were observed. Uni-modal distributions were often observed for the accumulation mode. In the case of Aitken, the occurrence of bi-modal distributions was relatively more frequent with two groups of particles: either non- or less-hygroscopic (GF = 1.0 to 1.2) and more-hygroscopic (GF = ~1.5). Closure between the measured GFs and predictions based on chemical composition measured by Aerosol Mass Spectrometer will also be discussed.
We also performed RH scanning to measure the GFs as a function of RH (both deliquescence and efflorescence branches) with the purpose of understanding the hygroscopic behaviors of aerosols at lower RHs. Although many of the previous studies reported continuous water-uptake behaviors without obvious deliquescence, we observed hygroscopic hysteresis in most cases. GF parameterizations will be applied for various meteorological periods and groups of chemical composition, which are useful to modeling the hygroscopic GFs for various ambient conditions and chemical composition.
This work was supported by the University Grants Committee (SEG-HKUST07) and the Environmental Conservation Funds (ECF) of Hong Kong (ECWW09EG04)