Particle size distribution and new particle formation under influence of biomass burning at a high altitude background site of Mt. Yulong (3410m) in China

Abstract

Biomass burning (BB) activities have a great impact on particle number size distribution (PNSD) in upper troposphere of Tibet-Plateau, which could affect regional and global climate. The intensive campaign for the measurement of PNSD, gaseous pollutants and meteorological parameters was conducted at Mt. Yulong, a high-altitude site (3410 m a. s. l.) in the southeast of Tibet Plateau during the pre-monsoon season (22 March to 15 April), when the intensive BB activities in South Asia were observed by fire maps. Long-range transport of BB pollutants could increase the accumulation mode particles in background atmosphere of Mt. Yulong. As a consequence, cloud condensation nuclei (CCN) concentration was found to be 2-8 times higher during BB periods than that during clean period. Apart from BB, variation of planet boundary layer (PBL) and new particle formation were other factors that influenced PNSD. However, only 3 NPF events (with a frequency of 14 %) were observed at Mt. Yulong. Occurrence of NPF events during clean episode corresponded with elevated PBL or transported BB pollutants. Due to lack of condensable vapors including sulfuric acid and organic compounds, the newly formed particles were not able to grow to CCN size. Our study emphasized the influences of BB on aerosol and CCN concentration in atmosphere of Tibet Plateau. These results can improve our understanding of the variation of particle concentration in upper troposphere, and provide information for regional and global climate models.