Biomass burning emits large amounts of both trace gases and particles into the atmosphere. It plays a profound role in regional air quality and climate change. In the present study, an intensive campaign was carried out at an urban site in Beijing, China, in June 2014, which covered the winter wheat harvest season over the North China Plain (NCP). Meanwhile, two evident biomass-burning events were observed. A clear burst in ultrafine particles (below 100 nm in diameter, PM1) and subsequent particle growth took place during the events. With the growth of the ultrafine particles, the organic fraction of PM1 increased significantly. The ratio of oxygen to carbon (O:C), which had an average value of 0.23 +/- 0.04, did not show an obvious enhancement, indicating that a significant chemical aging process of the biomass-burning aerosols was not observed during the course of events. This finding might have been due to the fact that the biomass-burning events occurred in the late afternoon and grewduring the nighttime, which is associated with a low atmospheric oxidation capacity. On average, organics and black carbon (BC) were dominant in the biomass-burning aerosols, accounting for 60 +/- 10% and 18 +/- 3% of PM1. The high organic and BC fractions led to a significant suppression of particle hygroscopicity. Comparisons among hygroscopicity tandem differential mobility analyzer (HTDMA)-derived, cloud condensation nuclei counter (CCNc)-derived, and aerosol mass spectrometer-based hygroscopicity parameter (kappa) values were consistent. The mean. values of biomass-burning aerosols derived from both HTDMA and CCNc measurements were approximately 0.1, regardless of the particle size, indicating that the biomass-burning aerosols were less active. The burst in particle count during the biomass-burning events resulted in an increased number of cloud condensation nuclei (CCN) at supersaturation (SS)= 0.2-0.8%. (C) 2016 Elsevier B.V. All rights reserved.
ISI Document Delivery No.: EJ6HPTimes Cited: 5Cited Reference Count: 55Wu, Zhijun Zheng, Jing Wang, Yu Shang, Dongjie Du, Zhoufei Zhang, Yuanhang Hu, MinWu, Zhijun/A-7041-2012; Zhang, Yuanhang/F-7038-2011National Natural Science Foundation of China [91544214, 21190052, 41121004, 41475127]; National Basic Research Program of China [2013CB228503]; Special Fund of the State Key Joint Laboratory of Environment Simulation and Pollution Control [14L02ESPC]; Ministry of Environmental Protection, The People's Republic of China ; Collaborative Innovation Center for Regional Environmental QualityThis work was supported by the following agencies: National Natural Science Foundation of China (91544214, 21190052, 41121004, and 41475127), National Basic Research Program of China (2013CB228503), Special Fund of the State Key Joint Laboratory of Environment Simulation and Pollution Control (14L02ESPC), the non-profit research projects of the Ministry of Environmental Protection, The People's Republic of China (201409010), and the Collaborative Innovation Center for Regional Environmental Quality. Great thanks to Mr. Ying Chen for useful discussions.663Elsevier science bvAmsterdam1879-1026