Continuous multi-component MAX-DOAS observations for the planetary boundary layer ozone variation analysis at Chiba and Tsukuba, Japan, from 2013 to 2019

Hitoshi Irie,Hossain Mohammed Syedul Hoque,Syuichi Itahashi,Kengo Sudo,Alessandro Damiani,Daichi Yonekawa

doi:10.1186/s40645-021-00424-9

Abstract

Ground-based remote sensing using multi-axis differential optical absorption spectroscopy (MAX-DOAS) was used to conduct continuous simultaneous observations of ozone (O3), nitrogen dioxide (NO2), and formaldehyde (HCHO) concentrations at Chiba (35.63° N, 140.10° E, 21 m a.s.l.) and Tsukuba (36.06° N, 140.13° E, 35 m a.s.l.), Japan, for 7 years from 2013 to 2019. These are urban and suburban sites, respectively, in the greater Tokyo metropolitan area. NO2 and HCHO are considered to be proxies for nitrogen oxides (NOx) and volatile organic compounds (VOCs), respectively, both of which are major precursors of tropospheric O3. The mean concentrations below an altitude of 1 km were analyzed as planetary boundary layer (PBL) concentrations. For a more spatially representative analysis around the urban area of Chiba, four MAX-DOAS instruments directed at four different azimuth directions (north, east, west, and south) were operated simultaneously and their data were unified. During the 7-year period, the satellite observations indicated an abrupt decrease in the tropospheric NO2 concentration over East Asia, including China. This suggested that the transboundary transport of O3 originating from the Asian continent was likely suppressed or almost unchanged during the period. Over this time period, the MAX-DOAS observations revealed the presence of almost-constant annual variations in the PBL O3 concentration, whereas reductions in NO2 and HCHO concentrations occurred at rates of approximately 6–10%/year at Chiba. These changes provided clear observational evidence that a decreasing NOx concentration significantly reduced the amount of O3 quenched through NO titration under VOC-limited conditions in the urban area. Under the dominant VOC-limited conditions, the MAX-DOAS-derived concentration ratio of HCHO/NO2 was found to be below unity in all months. Thus, the multi-component observations from MAX-DOAS provided a unique data set of O3, NO2, and HCHO concentrations for analyzing PBL O3 variations.

Highlights

Ozone (O3) plays a critical role in the troposphere as a photochemical oxidant with harmful impacts on human health and as the third most important greenhouse gas
Recent concentration trends in Japan have indicated the existence of a paradox (Akimoto 2017), in which the concentration of surface O3 has increased despite a decrease in the concentrations of its major precursors, namely nitrogen oxides (NOx ≡ nitric oxide [NO] + nitrogen dioxide [NO2]) and volatile organic compounds (VOCs)
Because we focused on the planetary boundary layer (PBL), it was expected that the multi-component observations from MAX-Differential optical absorption spectroscopy (DOAS) would provide a unique O3, NO2, and HCHO data set for analyzing O3 variations in the PBL

Summary

Introduction

Ozone (O3) plays a critical role in the troposphere as a photochemical oxidant with harmful impacts on human health and as the third most important greenhouse gas. Recent concentration trends in Japan have indicated the existence of a paradox (Akimoto 2017), in which the concentration of surface O3 has increased despite a decrease in the concentrations of its major precursors, namely nitrogen oxides (NOx ≡ nitric oxide [NO] + nitrogen dioxide [NO2]) and volatile organic compounds (VOCs). For China, Li et al (2019) estimated that anthropogenic NOx emissions decreased by 21% from 2013 to 2017 and there was little change in VOC emissions Under such conditions, an analysis of observation data from ~1000 sites in China showed a slight increasing trend in ambient O3 concentrations of 1–3 ppbv/ year in the megacity clusters of eastern China only and a decreasing trend in the southern parts of China (Li et al 2019). A determination of the causes leading to the O3 trend would improve our quantitative understanding of the processes leading to the variation in O3 concentrations and the development of a SLCP co-control policy

Methods

Results

Conclusion