Browsing by Subject "URBAN ATMOSPHERE"

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  • Chu, Biwu; Kerminen, Veli-Matti; Bianchi, Federico; Yan, Chao; Petäjä, Tuukka; Kulmala, Markku (2019)
    New particle formation (NPF) studies in China were summarized comprehensively in this paper. NPF frequency, formation rate, and particle growth rate were closely compared among the observations carried out at different types of sites in different regions of China in different seasons, with the aim of exploring the nucleation and particle growth mechanisms. The interactions between air pollution and NPF are discussed, emphasizing the properties of NPF under heavy pollution conditions. The current understanding of NPF cannot fully explain the frequent occurrence of NPF at high aerosol loadings in China, and possible reasons for this phenomenon are proposed. The effects of NPF and some aspects of NPF research requiring further investigation are also summarized in this paper.
  • Viippola, Viljami; Yli-Pelkonen, Vesa; Järvi, Leena; Kulmala, Markku; Setälä, Heikki (2020)
    Trees and other vegetation have been advocated as a mitigation measure for urban air pollution mainly due to the fact that they passively filter particles from the air. However, mounting evidence suggests that vegetation may also worsen air quality by slowing the dispersion of pollutants and by producing volatile organic compounds that contribute to formation of ozone and other secondary pollutants. We monitored nanoparticle (>10 nm) counts along distance gradients away from major roads along paired transects across open and forested landscapes in Baltimore (USA), Helsinki (Finland) and Shenyang (China) − i.e. sites in three biomes with different pollution levels − using condensation particle counters. Mean particle number concentrations averaged across all sampling sites were clearly reduced (15 %) by the presence of forest cover only in Helsinki. For Baltimore and Shenyang, levels showed no significant difference between the open and forested transects at any of the sampling distances. This suggests that nanoparticle deposition on trees is often counterbalanced by other factors, including differing flow fields and aerosol processes under varying meteorological conditions. Similarly, consistent differences in high frequency data patterns between the transects were detected only in Helsinki. No correlations between nanoparticle concentrations and solar radiation or local wind speed as affecting nanoparticle abundances were found, but they were to some extent associated with canopy closure. These data add to the accumulating evidence according to which trees do not necessarily improve air quality in near-road environments.
  • Nie, W.; Ding, A. J.; Xie, Y. N.; Xu, Z.; Mao, H.; Kerminen, V. -M.; Zheng, L. F.; Qi, X. M.; Huang, X.; Yang, X. -Q.; Sun, J. N.; Herrmann, E.; Petäjä, T.; Kulmala, M.; Fu, C. B. (2015)
  • Ye, Chunxiang; Zhou, Xianliang; Pu, Dennis; Stutz, Jochen; Festa, James; Spolaor, Max; Tsai, Catalina; Cantrell, Christopher; Mauldin, Roy L.; Weinheimer, Andrew; Hornbrook, Rebecca S.; Apel, Eric C.; Guenther, Alex; Kaser, Lisa; Yuan, Bin; Karl, Thomas; Haggerty, Julie; Hall, Samuel; Ullmann, Kirk; Smith, James; Ortega, John (2018)
    Here we report the measurement results of nitrous acid (HONO) and a suite of relevant parameters on the NCAR C-130 research aircraft in the southeastern US during the NOMADSS 2013 summer field study. The daytime HONO concentration ranged from low parts per trillion by volume (pptv) in the free troposphere (FT) to mostly within 5-15 pptv in the background planetary boundary layer (PBL). There was no discernible vertical HONO gradient above the lower flight altitude of 300m in the PBL, and the transport of ground surface HONO was not found to be a significant contributor to the tropospheric HONO budget. The total in situ HONO source mean (+/- 1 SD) was calculated as 53 (+/- 21) pptv h(-1) during the day. The upper-limit contribution from NOx-related reactions was 10 (+/- 5) pptv h(-1), and the contribution from photolysis of particulate nitrate (pNO(3)) was 38 (+/- 23) pptv h(-1), based on the measured pNO(3) concentrations and the median pNO(3) photolysis rate constant of 2.0 x 10 4 s(-1) determined in the laboratory using ambient aerosol samples. The photolysis of HONO contributed to less than 10% of the primary OH source. However, a recycling NOx source via pNO(3) photolysis was equivalent to similar to 2.3 x 10(-6) molm(-2) h(-1) in the air column within the PBL, a considerable supplementary NOx source in the low-NOx background area. Up to several tens of parts per trillion by volume of HONO were observed in power plant and urban plumes during the day, mostly produced in situ from precursors including NOx and pNO(3). Finally, there was no observable accumulation of HONO in the nocturnal residual layer and the nocturnal FT in the background southeastern US, with an increase in the HONO / NOx ratio of