Browsing by Subject "GROUND-LEVEL"

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  • Du, Wei; Dada, Lubna; Zhao, Jian; Chen, Xueshun; Dällenbach, Kaspar; Xie, Conghui; Wang, Weigang; He, Yao; Cai, Jing; Yao, Lei; Zhang, Yingjie; Wang, Qingqing; Xu, Weiqi; Wang, Yuying; Tang, Guiqian; Cheng, Xueling; Kokkonen, Tom V.; Zhou, Wei; Yan, Chao; Chu, Biwu; Zha, Qiaozhi; Hakala, Simo; Kurppa, Mona; Jarvi, Leena; Liu, Yongchun; Li, Zhanqing; Ge, Maofa; Fu, Pingqing; Nie, Wei; Bianchi, Federico; Petäjä, Tuukka; Paasonen, Pauli; Wang, Zifa; Worsnop, Douglas R.; Kerminen, Veli-Matti; Kulmala, Markku; Sun, Yele (2021)
    The role of new particle formation (NPF) events and their contribution to haze formation through subsequent growth in polluted megacities is still controversial. To improve the understanding of the sources, meteorological conditions, and chemistry behind air pollution, we performed simultaneous measurements of aerosol composition and particle number size distributions at ground level and at 260 m in central Beijing, China, during a total of 4 months in 2015-2017. Our measurements show a pronounced decoupling of gas-to-particle conversion between the two heights, leading to different haze processes in terms of particle size distributions and chemical compositions. The development of haze was initiated by the growth of freshly formed particles at both heights, whereas the more severe haze at ground level was connected directly to local primary particles and gaseous precursors leading to higher particle growth rates. The particle growth creates a feedback loop, in which a further development of haze increases the atmospheric stability, which in turn strengthens the persisting apparent decoupling between the two heights and increases the severity of haze at ground level. Moreover, we complemented our field observations with model analyses, which suggest that the growth of NPF-originated particles accounted up to similar to 60% of the accumulation mode particles in the Beijing-Tianjin-Hebei area during haze conditions. The results suggest that a reduction in anthropogenic gaseous precursors, suppressing particle growth, is a critical step for alleviating haze although the number concentration of freshly formed particles (3-40 nm) via NPF does not reduce after emission controls.
  • Mäkelä, Jakke Sakari; Lakkala, Kaisa; Koskela, Tapani; Karppinen, Tomi; Karhu, Juha Matti; Savastiouk, Vladimir; Suokanerva, Hanne; Kaurola, Jussi; Arola, Antti; Lindfors, Anders Vilhelm; Meinander, Outi; De Leeuw, Gerrit; Heikkilä, Anu (2016)
    The data flow involved in a long-term continuous solar spectral UV irradiance monitoring program is investigated and structured to provide an overall view on the multiphase process from data acquisition to the final products. The program employing Brewer spectrophotometers as measuring instruments is maintained by the Finnish Meteorological Institute (FMI) ever since the 1990s at two sites in Finland: Sodankyla (67 degrees N) and Jokioinen (61 degrees N). It is built upon rigorous operation routines, processing procedures, and tools for quality control (QC) and quality analysis (QA) under continuous development and evaluation. Three distinct levels of data emerge, each after certain phase in the data flow: Level 0 denoting raw data, Level 1 meaning calibrated data processed in near-real time, and Level 2 comprising of postprocessed data corrected for all distinguishable errors and known inaccuracies. The final products disseminated to the users are demonstrated to result from a process with a multitude of separate steps, each required in the production of high-quality data on solar UV radiation at the Earth's surface.