Characteristics Of Atmospheric Fine And Ultrafine Particle Number Size Distribution During Speical Period In Beijing

With the rapid urbanization of China, large cities including Beijing as the representative have been experiencing severe atmospheric particulate matter pollution. Atmospheric fine particles and ultrafine particles have important impacts on visibility impairment, health damage and global and regional climate. In recent years, Beijing has been committed to improve the energy structure and reduce coal-fired and vehicle emissions. Furthermore, a series of stringent emission control measures have been taken during the special periods when international events were hosted to achieve good air qualities. Long-term observation in-depth analysis of the atmospheric particle number size distribution are helpful in evaluating the particulate matter pollution status and control strategy development. Therefore, based on the in-situ measurements of atmospheric particle physical properties during the 2008 Beijing Olympic games,2014 Asia-Pacific Economic Cooperation conference and 2015 Victory Day Military Parade period, the number size distribution of atmospheric fine particles and ultrafine particles and its variation during the special reduction period were analyzed in this study.1) The variation of number size distribution of atmospheric particles and regional PM2.5 distribution before, during and after the special reduction period were analyzed to support the scientific evaluation of effect of temporary emission control measures. The total particle number concentration of Olympic, APEC and Parade period were (6.0 ±3.1)×103 cm-3, (4.7±3.2)×103 cm-3 and (6.1±3.2)×103 cm-3, respectively. Accumulation mode particles (0.1-1 μm) had experienced the most reduction during the special reduction period, which were 40%、49% and 48% compared to that before the period. The mean PM2.5 concentration had decreased by 52.0%、60.5% and 72.3% in Beijing during the special reduction period, while the mean concentration of regional PM2.5 surrounding Beijing (13 cities in the Jing-Jin-Ji area) had decreased by 40.0% and 59.0% during the APEC and Parade period.2) The variation in the effect of temporary emission control measures taken during the special reduction period in Beijing and surrounding regions was analyzed to provide scientific advices for the development of regional control strategies in the future. The effect of temporary emission control measures taken during the special reduction period in Beijing and surrounding regions was upgrading among the three special reduction periods, and this was closely related to the emission control strategy improvement, meteorological conditions and seasonal levels.The strategy of "Joint Prevention and Control of Air Pollution" promoted the upgrading of the regional emission reduction. The advantageous meteorological conditions contributed certainly to the good air quality during the APEC and Parade period. The atmospheric background particle concentration in autumn was much higher than that in summer, result in the high concentration of accumulation mode particle during the APEC period.3) The seasonal variation of atmospheric particle number size distribution and its sources in 2015 were analyzed. The regional transport through southwest contributed certainly to the number concentration of Aitken mode and accumulation mode particles in summer, while local emissions contributed mainly in winter. The total particle number concentration in winter was 44.7% higher than that in summer, Aitken mode particles contributed mainly to the difference. The local emitted Aitken mode particles had an important contribution to the haze formation in winter.4) The characteristics of new particle formation during the special reduction period were analyzed to get a better understanding of the formation and growth of the new particles in Beijing. The implementation of the emission control measures was conducive to new particle formation, while the formation and effective growth of new particles have an important contribution to the increase of atmospheric background particle concentration. It was when the background particle concentration was sufficiently high (more than 10000 cm-3) that prohibit the formation of new particles. The condensational growth takes precedence over the coagulational growth. Rapid reduction of the total number concentration of particles (greater than 50 cm-3 min-1) and the correlation between GMD and CS as well as CoagS (lower than 50%) was an important indicator of the coagulational growth contributing to the growth of particles. In addition, besides local formation of atmospheric new particles, regional transported nucleation precursor would contribute to atmospheric new particles by plume nucleation.