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Abstract:
Formaldehyde(HCHO), a key aerosol precursor,plays a significant role in atmospheric photo-oxidation pathways.In this study,HCHO column densities were measured using Multi-axis Differential Optical Absorption Spectroscopy (MAX-DOAS) instrument at the University of Chinese Academy of Science (UCAS) in Huairou District, Beijing, which is about 50 km away from the city center, during the period of October 1, 2014 to December 31,2014, in which the 20 Asia-Pacific Economic Cooperation (APEC) summit was organized on 3 to 12 November. Peak values of HCHO vertical column densities (VCDs) around noon and a good correlation coefficient of 0.87 between HCHO and O3 indicate that the secondary sources of HCHO through photochemical reactions of volatile organic compounds (VOCs) dominate HCHO values in the area around UCAS. Dependences of HCHO VCDs on wind fields and backward trajectories
were identified and indicated that the HCHO values in the area around UCAS were considerably affected by the transports of pollutants (VOCs) from polluted area in the south. The effects of control measures on HCHO VCDs during the APEC period were evaluated . During the period of APEC conference, the averaged HCHO is 37.95% and 30.75% lower than that during the pre-APEC and post-APEC period, respectively. The phenomenon could be attributed to both effects of prevailing northwest wind fields during the APEC and strict control measures . We also compared the MAX-DOAS results with the Atmosphere Monitoring Service (CAMS) model. The CAMS model and MAX-DOAS results are generally consistent with a good correlation coefficient of ~ 0.83 . The peak values are well consistently captured by both data sets, but the low values are systematically underestimated by the CAMS model .
The finding indicates the CAMS model can well simulate the effects of transports and the secondary sources of HCHO, but underestimate the local primary sources.
