Rapid aerosol particle growth and increase of cloud condensation nucleus activity by secondary aerosol formation and condensation: A case study for regional air pollution in northeastern China

Abstract

[1] This study was part of the international field measurement Campaigns of Air Quality Research in Beijing and Surrounding Region 2006 (CAREBeijing-2006). We investigated a new particle formation event in a highly polluted air mass at a regional site south of the megacity Beijing and its impact on the abundance and properties of cloud condensation nuclei (CCN). During the 1-month observation, particle nucleation followed by significant particle growth on a regional scale was observed frequently ($30%), and we chose 23 August 2006 as a representative case study. Secondary aerosol mass was produced continuously, with sulfate, ammonium, and organics as major components. The aerosol mass growth rate was on average 19 mg m À3 h À1 during the late hours of the day. This growth rate was observed several times during the 1-month intensive measurements. The nucleation mode grew very quickly into the size range of CCN, and the CCN size distribution was dominated by the growing nucleation mode (up to 80% of the total CCN number concentration) and not as usual by the accumulation mode. At water vapor supersaturations of 0.07-0.86%, the CCN number concentrations reached maximum values of 4000-19,000 cm À3 only 6-14 h after the nucleation event. During particle formation and growth, the effective hygroscopicity parameter k increased from about 0.1-0.3 to 0.35-0.5 for particles with diameters of 40-90 nm, but it remained nearly constant at $0.45 for particles with diameters of $190 nm. This result is consistent with aerosol chemical composition data, showing a pronounced increase of sulfate. Citation: Wiedensohler, A., et al. (2009), Rapid aerosol particle growth and increase of cloud condensation nucleus activity by secondary aerosol formation and condensation: A case study for regional air pollution in northeastern China,

Enhanced organic mass fraction and decreased hygroscopicity of cloud condensation nuclei (CCN) during new particle formation events

“…Reduced hygroscopicity of newly formed particles can be expected where SOA plays a major role in particle growth, e.g., over boreal and tropical forests [Tunved et al, 2006;Gunthe et al, 2009]. In other regions, such as polluted megacities, high proportions of inorganic compounds may enhance the hygroscopicity of CCN [Wiedensohler et al, 2009].…”

“…Ambient measurements and modeling studies suggest that nucleated particles can grow into the size range of cloud condensation nuclei (CCN) in various environments ranging from remote continental to highly polluted [Kerminen et al, 2005;Laaksonen et al, 2005;Pirjola et al, 2002;Wang and Penner, 2009;Kuang et al, 2009;Wiedensohler et al, 2009]. Recently, it has been proposed that nucleation of new particles happens by activation of thermodynamically stable clusters that are either charged [Horrak et al, 1998;Kulmala et al, 2000;Yu and Turco, 2008] or neutral [Kulmala et al, 2007], and continually present in the atmosphere.…”

Impacts of new particle formation on aerosol cloud condensation nuclei (CCN) activity in Shanghai: case study

“…reported that the GR of sulfur-poor NPF was on average about 80 % larger than that of sulfur-rich NPF, and that the NPF events increased CCN by 0.4-6 times in Beijing, where various source apportionments of PM 2.5 were reported by Zhang et al (2013). Wiedensohler et al (2009) found that the CCN size distribution is dominated by the growing nucleation mode in Beijing, which accounted for up to 80 % of the total CCN number concentration, in contrast to the usually found phenomenon of the dominance by the accumulation mode.…”

“…The newly formed particles from atmospheric nucleation are often able to grow into CCN size and further influence cloud properties or even global climate Laaksonen et al, 2005;Wiedensohler et al, 2009). Kerminen et al (2012) present a synthesis of our current (end of 2012) knowledge on CCN production associated with atmospheric nucleation, and conclude that CCN production associated with atmospheric nucleation is both a frequent and widespread phenomenon in numerous types of continental boundary layers, and probably also for a large fraction of the free troposphere.…”

Elucidating severe urban haze formation in China

“…Also, primary and secondary particles undergo chemical and physical transformations and are subjected to cloud processing and transport in the atmosphere (8,9). The formation mechanisms leading to severe haze episodes with exceedingly high PM 2.5 levels in China remain highly uncertain, and the abundance and chemical constituents of PM 2.5 vary considerably, depending on complex interplay between meteorology, pollution sources, and atmospheric chemical processes (10)(11)(12)(13)(14)(15)(16). For example, on the basis of ambient measurements and receptor model analysis, the contribution to the annual mean PM 2.5 in Beijing has been suggested to be mainly from industrial pollution and secondary inorganic aerosol formation, but negligibly from traffic emissions (14).…”