Aging and hygroscopicity variation of black carbon particles in Beijing measured by a quasi-atmospheric aerosol evolution study (QUALITY) chamber
Institutional Repository Document
Overview
Research
Identity
Other
View All
Overview
abstract
Abstract. Measurements of aging and hygroscopicity variation of black carbon (BC) particles in Beijing were conducted using a 1.2m3 quasi-atmospheric aerosol evolution study (QUALITY) chamber, which consisted of a bottom flow chamber where ambient air was pulled through continuously and an upper reaction chamber where aging of BC particles occurred. Within the reaction chamber, transmission of the solar ultraviolet irradiation was approximately 50%60%, wall loss of primary gaseous pollutants was negligible, and BC exhibited a half-lifetime about 37 hours. Typically, equilibrium for the primary gases, temperature, and relative humidity between the reaction chamber and ambient air was established within 1 hour. Rapid growth of BC particles was observed, with an average total growth of 7733nm and average growth rate of 2611nmh1. Secondary organic aerosol (SOA) accounted for more than 90% of the coating mass. The O/C ratio of SOA was 0.5, lower than the ambient level. The hygroscopic growth factor of BC particles decreased slightly with an initial thin coating layer because of BC reconstruction, but subsequently increased to 1.061.08 upon further aging. The (kappa) values for BC particles and coating materials were calculated as 0.035 and 0.040 at the subsaturation and supersaturation conditions, respectively, indicating low hygroscopicity of coated SOA on BC particles. Hence, our results indicate that initial photochemical aging of BC particles does not appreciably alter the particle hygroscopicity in Beijing.
