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

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.

Comment on acp-2022-110

“…2). As shown in a recent study (Irie et al, 2021), both NO2 and HCHO were reduced and O3 recovered slightly during the period of 2013-2019. Any potential COVID-related effects in 2020 were superimposed over these trends.…”

“…2). Most of this large urban area is expected to be under VOC-limited conditions (Akimoto, 2017;Irie et al, 2021). In this study, we apply an integrated approach that exploits various independent datasets retrieved from multiple platforms, including observations of NO2, O3, and HCHO (as a proxy for non-methane VOC, NMVOC) from two sites equipped with Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) systems located in urban and suburban areas.…”

“…In this study, partial vertical columns of O3, NO2, and HCHO concentrations below 1 km were used. Notably, due to the contribution of upper troposphere/lower stratosphere (UT/LS) O3 to differential slant column densities, only data collected at a solar zenith angle (SZA) below 50° can be used for O3 retrieval (Irie et al 2011(Irie et al , 2021. Therefore, the ozone dataset employed here was limited to the period of March-October.…”

Peculiar COVID-19 effects in the Greater Tokyo Area revealed by spatiotemporal variabilities of tropospheric gases and light-absorbing aerosols

“…In this study, partial vertical columns of O 3 , NO 2 , and HCHO concentrations below 1 km were used. Notably, due to the contribution of upper troposphere-lower stratosphere (UTLS) O 3 to differential slant column densities, only data collected at a solar zenith angle (SZA) below 50 • can be used for O 3 retrieval (Irie et al, 2011(Irie et al, , 2021. Therefore, the ozone dataset em-ployed here was limited to the period of March-October.…”

“…In addition to the NIES dataset, we used observations of black carbon (BC) concentrations recorded by the continuous soot-monitoring system (COSMOS) (Kondo et al, 2009;Damiani et al, 2021) deployed at Chiba University site in November 2019. Our analysis focused on observations recorded in 2020.…”