MAX-DOAS Network in China and Its Applications

Entering the “14th Five-Year Plan”, the coordinated control of PM2.5 and O3 has become a major issue of air pollution prevention and control in China. In order to achieve this goal, the stereoscopic monitoring of regional PM2.5 and O3 and their precursors (NO2, HCHO etc.) is extremely necessary. Yet, current monitoring networks are inadequate to monitor the vertical profiles of all above atmospheric compositions simultaneously, and to support air quality control. We have established a nationwide ground-based hyperspectral stereoscopic remote sensing network based on MAX-DOAS since 2015. This monitoring network provides a significant opportunity for the regional coordinated control of PM2.5 and O3 in China. One-year vertical profiles of aerosol, NO2, HCHO and O3 monitored from four MAX-DOAS stations (CAMS, SH_XH, SUST and CQ) installed in four megacities (Beijing, Shanghai, Shenzhen and Chongqing) are used to characterize their vertical distribution differences in four key regions of Jing-Jin-Ji (JJJ), Yangtze River Delta (YRD), Pearl River Delta (PRD) and Sichuan Basin (SB), respectively. The normalized and yearly averaged aerosol vertical profiles in JJJ and PRD exhibit a box shape under 400 m and a Gaussian shape, respectively, and they all show exponential shapes in YRD and SB. The NO2 vertical profiles in four regions all exhibit exponential shapes due to the obvious vehicle emissions. The shape of HCHO vertical profile in JJJ and PRD shows Gaussian, and it exhibits exponential shape in YRD and SB. The averaged O3 vertical profiles in four regions all exhibit box shape and linear shape in pollution and non-pollution periods, respectively. Moreover, a regional transport event occurred at an altitude of 600-1000 m was monitored in the southwest-northeast pathway of North China Plain (NCP) by five MAX-DOAS stations (SJZ, WD, NC, CAMS and UCAS) belonging to above network. The aerosol optical depths (AOD) in these five stations varied in the order of SJZ > WD > NC > CAMS > UCAS. The short-distance regional transport of NO2 in 800 m layer was monitored between WD and NC. As an important precursor of secondary aerosol, NO2 air mass in WD and NC all occurred 1 hr earlier than aerosol. Similarly, the short-distance regional transport of HCHO in 800 m layer between NC and CAMS, and it potentially affected the O3 concentration in Beijing. Finally, CAMS was selected as a typical site to learn O3-NOx-VOCs sensitivities in vertical space. We found the production of O3 changed from predominantly VOC-limited condition to mainly mixed VOC-NOx-limited condition from 0-100 m layer to 200-300 m layer. In addition, the downward transport of O3 could make a contribute to the increase of ground surface O3 concentration. ground-based hyperspectral stereoscopic remote sensing network provide a promising strategy to support PM2.5 and O3 and their precursors management and attribution of sources.