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Chen et al. (2022) analyzed the event of rapid nocturnal O 3 enhancement (NOE) observed on 31 July 2021 at the surface level in the North China Plain and proposed transport of substantial stratosphere ozone to the surface by Typhoon In-fa followed by downdraft of shallow convection as the mechanism of the NOE event. The analysis seems to be valid from the viewpoint of atmospheric physics. This comment revisits the NOE phenomenon on the basis of the China National Environmental Monitoring Center (CNEMC) network data used in Chen et al. (2022), together with the CNEMC data from Zibo (ZB) and O 3 , NO x , PAN (peroxyacetic nitric anhydride), and VOC (volatile organic compound) data from the Zibo supersite operated by the China Research Academy of Environmental Sciences (CRAES). We found (a) O x (O 3 + NO 2) levels during the NOE period approaching those of O 3 during 14:00–17:00 LT, (b) levels of PAN and the relationship between O 3 and PAN consistent with dominance of chemical and physical processes within the boundary layer, and (c) estimated photochemical ages of air mass shorter than 1 d and showing no drastic increases during the NOE. We argue that the NOE was not caused by typhoon-induced stratospheric intrusion but originated from fresh photochemical production in the lower troposphere. Our argument is well supported by the analysis of atmospheric transport as well as ground-based remote sensing data. [ABSTRACT FROM AUTHOR]

Environment context: One-year-long on-line measurements of surface O3 and CO mixing ratios were performed on the southeast Tibetan Plateau to examine O3 behaviour. During the daytime, the O3 mixing ratio was strongly affected by vertical air exchange. The O3 mixing ratio was high in the afternoon and decreased at night, indicating a sink of tropospheric O3. The upper limit of the tropospheric O3 sink averaged from 4.5 to 5.5 ppb h−1. Rationale: Ozone (O3) behaviour over the Tibetan Plateau has attracted attention in recent decades. However, few long-term measurements have been performed in the region. Methodology: Field observations were conducted at a mountain site on the southeastern Tibetan Plateau from June 2014 to July 2015 in order to understand the behaviour of surface O3 and its influencing factors. Backward trajectory cluster analysis was applied to understand long-range transport sources and their relative contributions. Results: The monthly average O3 ranged from 22.1 to 48.6 ppb with a common high spring ozone concentration phenomenon. The O3 diurnal variation exhibited a similar pattern to those in polluted areas but the cause was different. The O3 mixing ratio was significantly positively correlated with mixed-layer depth and wind speed, and negatively with temperature and relative humidity, indicating strong vertical air exchange. Approximately 50% of air mass trajectories originated from the northeastern Bengal Bay region, with fairly low O3 (CO) mixing ratios and high humidity. Others originated from the north Indian subcontinent (28%) and the Middle East (18%), with fairly high O3 (and CO) and low humidity. Discussion: The average relative contributions of different air masses to surface O3 and CO were small and scattered but large for trajectories arriving at 14:00 hours when vertical air exchange was close to its strongest for the day. The tropospheric O3 sink may be common in the highlands, indicating a negative greenhouse effect there. The O3 sink at Linzhi was estimated in the range of 4.5–5.5 ppb h−1 at maximum. Summary. One-year-long on-line measurements of surface O3 and CO mixing ratios were performed on the southeast Tibetan Plateau to examine O3 behaviour. During the daytime, the O3 mixing ratio was strongly affected by vertical air exchange. The O3 mixing ratio was high in the afternoon and decreased at night, indicating a sink of tropospheric O3. The upper limit of the tropospheric O3 sink averaged from 4.5 to 5.5 ppb h−1. [ABSTRACT FROM AUTHOR]

Tropospheric ozone plays an important role in atmospheric processes. However, the acquisition of tropospheric ozone content from satellite observations is a crucial challenge for atmospheric pollution research. In this study, the 0.25° × 0.25° tropospheric ozone column products over China were determined from total ozone columns measured by the Ozone Monitoring Instrument (OMI) and ozone profiler of the Microwave Limb Sounder (MLS). Calculation results were then validated with similar satellite products, Electrochemical Concentration Cell (ECC) ozonesonde observations, and simulation results from the Regional Atmospheric Modelling System – Community Multiscale Air Quality Model (RAMS-CMAQ). Validations shows that OMI-MLS calculation results correlate well with ozonesonde data, the correlation coefficient reached to 0.92. Compared to RAMS-CMAQ, OMI-MLS presents consistent distribution and the correlation coefficients range from 0.52 to 0.82. [ABSTRACT FROM AUTHOR]

Inter-annual variability and long-term trends in tropospheric ozone are both environmental and climate concerns. Ozone measured at Mt Waliguan Observatory (WLG, 3816ma.s.l.) on the Tibetan Plateau over the period of 1994- 2013 has increased significantly by 0.2-0.3 ppbv yr-1 during spring and autumn but shows a much smaller trend in winter and no significant trend in summer. Here we explore the factors driving the observed ozone changes at WLG using backward trajectory analysis, chemistry-climate model hindcast simulations (GFDL AM3), a trajectory-mapped ozonesonde data set, and several climate indices. A stratospheric ozone tracer implemented in GFDL AM3 indicates that stratosphere-to-troposphere transport (STT) can explain ~60% of the simulated springtime ozone increase at WLG, consistent with an increase in the NW air-mass frequency inferred from the trajectory analysis. Enhanced STT associated with the strengthening of the mid-latitude jet stream contributes to the observed high ozone anomalies at WLG during the springs of 1999 and 2012. During autumn, observations at WLG are more heavily influenced by polluted air masses originating from South East Asia than in the other seasons. Rising Asian anthropogenic emissions of ozone precursors are the key driver of increasing autumnal ozone observed at WLG, as supported by the GFDL AM3 model with time-varying emissions, which captures the observed ozone increase (0.26±0.11 ppbv yr-1). AM3 simulates a greater ozone increase of 0.38±0.11 ppbv yr-1 at WLG in autumn under conditions with strong transport from South East Asia and shows no significant ozone trend in autumn when anthropogenic emissions are held constant in time. During summer, WLG is mostly influenced by easterly air masses, but these trajectories do not extend to the polluted regions of eastern China and have decreased significantly over the last 2 decades, which likely explains why summertime ozone measured at WLG shows no significant trend despite ozone increases in eastern China. Analysis of the Trajectory-mapped Ozonesonde data set for the Stratosphere and Troposphere (TOST) and trajectory residence time reveals increases in direct ozone transport from the eastern sector during autumn, which adds to the autumnal ozone increase. We further examine the links of ozone variability at WLG to the quasibiennial oscillation (QBO), the East Asian summer monsoon (EASM), and the sunspot cycle. Our results suggest that the 2-3-, 3-7-, and 11-year periodicities are linked to the QBO, EASM index, and sunspot cycle, respectively. A multivariate regression analysis is performed to quantify the relative contributions of various factors to surface ozone concentrations at WLG. Through an observational and modelling analysis, this study demonstrates the complex relationships between surface ozone at remote locations and its dynamical and chemical influencing factors. [ABSTRACT FROM AUTHOR]

We analyzed the temperature dependence of ozone absorption cross-sections in four data sets: the quadratic temperature data based on measurements of Bass and Paur (BPQ); data measured with the SCIAMACHY satellite spectrometer (SAC); data derived by Daumont, Brion, and Malicet (DBM); and data determined by Serdyuchenko et al. from the University of Bremen (SER). The ozone effective absorption coefficients of the Dobson and Brewer instruments at Kunming in the low-latitude stations and Hohenpeissenberg in the middle-latitude stations were calculated. The test of the total ozone column (TOC) from different ozone absorption cross-section data sets shows that in the Dobson and Brewer retrieval algorithms, the effect of temperature on the Brewer instrument is smaller than that for the Dobson instrument. The temperature sensitivity of the two instruments to the SAC is −0.005%°C−1 and 0.102%°C−1, respectively, indicating that the differences in the temperature sensitivity result in differences in the TOC measurements between the two instruments, as well as in systematic seasonal differences. Using BPQ, DBM and SER to retrieve TOC will increase the overall deviation of the two instruments by 2.5%, −2.77% and −1.89%, respectively. The consistency of the TOC retrieval in the two instruments is the best when using the SAC, which shows a deviation of only 0.03%. The systematic seasonal deviation can also be effectively improved. In addition, this work makes up for the lack of relevant research in low-latitude areas. The rangeability of the monthly mean value of the instrument system deviation at a low-latitude station is about one-half of that at the mid-latitude station (Kunming: 0.2%–1.1%, Hohenpeissenberg: 0.2%–2.0%). This is because the vertical distribution of the ozone and temperature varies in different latitudes, the seasonal variation in the middle and high latitudes is significant, and the effective temperature of ozone (T eff) in low latitudes changes little. Image 1 • The monthly variation of T eff at Kunming station is between −48.2 and −43.5 °C. • We tested the effect of using four kinds of data set to retrieve the TOC. • The two instruments retrieval algorithms have different temperature dependencies. • TOC created by them produced the most consistent when using the SAC. • At a low latitude, TOC retrieval is less affected by the T eff variation. [ABSTRACT FROM AUTHOR]