Abstract
Ground-based zenith scattered light differential optical absorption spectroscopy (DOAS) measurements were performed in summer and autumn (27 May–30 November) 2020 at Golmud (94°54′ E, 36°25′ N; 2807.6 m altitude) to investigate the abundances and temporal variations of ozone (O3) and its depleting substances over the northern Tibetan Plateau (TP). The differential slant column densities (dSCDs) of O3, nitrogen dioxide (NO2), bromine monoxide (BrO), and chlorine dioxide (OClO) were simultaneously retrieved from scattered solar spectra in the zenith direction during the twilight period. The O3 vertical column densities (VCDs) were derived by applying the Langley plot method, for which we investigated the sensitivities to the chosen wavelength, the a-priori O3 profile and the aerosol extinction profile used in O3 air mass factor (AMF) simulation as well as the selected solar zenith angle (SZA) range. The mean O3 VCDs from June to November 2020 are 7.21 × 1018 molec·cm−2 and 7.18 × 1018 molec·cm−2 at sunrise and sunset, respectively. The derived monthly variations of the O3 VCDs, ranging from a minimum of 6.9 × 1018 molec·cm−2 in October to 7.5 × 1018 molec·cm−2 in November, well matched the OMI satellite product, with a correlation coefficient R = 0.98. The NO2 VCDs at SZA = 90°, calculated by a modified Langley plot method, were systematically larger at sunset than at sunrise as expected with a pm/am ratio of ~1.56. The maximum of the monthly NO2 VCDs, averaged between sunrise and sunset, was 3.40 × 1015 molec·cm−2 in July. The overall trends of the NO2 VCDs were gradually decreasing with the time and similarly observed by the ground-based zenith DOAS and OMI. The average level of the BrO dSCD90°–80° (i.e., dSCD between 90° and 80° SZA) was 2.06 × 1014 molec·cm−2 during the period of June–November 2020. The monthly BrO dSCD90°–80° presented peaks in August and July for sunrise and sunset, respectively, and slowly increased after October. During the whole campaign period, the OClO abundance was lower than the detection limit of the instrument. This was to be expected because during that season the stratospheric temperatures were above the formation temperature of polar stratospheric clouds. Nevertheless, this finding is still of importance, because it indicates that the OClO analysis works well and is ready to be used during periods when enhanced OClO abundances can be expected. As a whole, ground-based zenith DOAS observations can serve as an effective way to measure the columns of O3 and its depleting substances over the TP. The aforementioned results are helpful in investigating stratospheric O3 chemistry over the third pole of the world.
Highlights
About 90% of atmospheric ozone (O3 ) is contained in the ozone layer at around 25 km height, which absorbs the solar ultraviolet radiation (UV) and heats the stratosphere [1].Following the discovery of the Antarctic ozone hole in 1985 [2] and the report of an indication of an ozone recovery in recent research, ozone and its depleting substances have been a focus of the scientific community (e.g., Solomon et al, 2016) [3]
On the basis of the final selected optimal air mass factor (AMF) simulation parameters, O3 vertical column densities (VCDs) from ground-based zenith differential optical absorption spectroscopy (DOAS) were obtained by the Langley plot method, and good agreement with Ozone Monitoring Instrument (OMI) satellite O3 VCD product is found indicating that the total O3 columns measured by zenith DOAS can be used for the validation of satellite products [65]
Ground-based zenith scattered light DOAS measurements were conducted in summer and autumn (27 May–30 November) 2020 at Golmud, a site in the northern Tibetan Plateau (TP)
Summary
About 90% of atmospheric ozone (O3 ) is contained in the ozone layer at around 25 km height, which absorbs the solar ultraviolet radiation (UV) and heats the stratosphere [1].Following the discovery of the Antarctic ozone hole in 1985 [2] and the report of an indication of an ozone recovery in recent research, ozone and its depleting substances have been a focus of the scientific community (e.g., Solomon et al, 2016) [3]. About 90% of atmospheric ozone (O3 ) is contained in the ozone layer at around 25 km height, which absorbs the solar ultraviolet radiation (UV) and heats the stratosphere [1]. Stratospheric ozone depleting reactions involve the hydrogen catalytic cycle, nitrogen catalytic cycle, and halogen catalytic cycles [4,5,6,7,8,9,10,11]. Nitrogen dioxide (NO2 ), bromine monoxide (BrO) and chlorine dioxide (OClO), as three key species of stratospheric ozone chemistry, have been widely measured to investigate the characteristics of temporal and spatial variation in stratospheric ozone chemistry [12]. Stratospheric ozone over the TP links with the temperatures at 200 hPa over the Earth’s three poles
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