Search

Under the background of global warming, the summer temperature of the North and Northeast China (NNEC) has significantly increased since 2017, which was accompanied by the aggravated ozone (O 3) pollution. In 2018, the NNEC experienced a record-breaking summer of the past 40 years. Influenced by the abnormal high temperatures, a regional ozone event occurred on 2-3 August, over 63% of 79 selected cities in the NNEC were exposed to O 3 pollution, and the maximum value of MDA8 O 3 reached 268 μg/m3. Observations indicated that ozone concentrations agree well with the maximum temperature at 2 meters (MT2M) over NNEC with a correlation coefficient of 0.69. During the pollution episode, strong downdraft in the local high (35°N-42.5°N, 112.5°E-132.5°E; LH) over the NNEC created the favourable meteorological conditions for O 3 formation. By analyzing the horizontal wind and wave activity fluxes (WAFs) at 200 hPa, we found that the LH formation was resulted from the Rossby wave propagation from upstream along the mid-latitude Asian jet. The split polar vortex intrusion further strengthened the amplitude of the Rossby wave and reinforced the LH. Moreover, a secondary circulation between Typhoon Jongdari and the LH contributed to the enhanced LH with strong subsidence. On the other hand, the stratospheric intrusions under the deep subsidence also contributed to the enhanced surface O 3. In this study, the deep-seated meteorological dynamical mechanisms contributing to the abnormal high temperatures were investigated, which can lead to a better understanding of the regional O 3 pollution over NNEC under the global-warming background. During the record-breaking summer in 2018, the NNEC region experienced regional O3 pollution in 27 July-3 August under extremely high-temperature conditions with other favorable meteorological conditions, and the deep subsidence over NNEC suppressed the dispersion of pollutants, further aggravating the pollution. By investigating the meteorological dynamics of this process, we found that the sinking motion was primarily induced by a quasi-barotropic LH, which was closely related to the propagation of the Rossby wave. Moreover, the activities of polar vortex and the secondary circulation between the LC and Typhoon Jongdari both facilitated the development of the LC. It should be noted the deep sinking motion of the secondary circulation not only intensified the LH, but also could deliver O 3 -rich air from the UTLS to the near-surface ground and directly led to the enhancement of O 3 over the NNEC region.A schematic representation of the meteorological mechanism for the regional ozone pollution over the NNEC is shown in the graphic abstract. [Display omitted] [ABSTRACT FROM AUTHOR]

The East Asian trough (EAT) is often regarded as an important controlling factor for the East Asian climate. However, there has been no detailed study of its effects on compound pollutants including PM 2.5 and O 3. This study investigates the possible effect of the intraseasonal EAT events on PM 2.5 and O 3 concentrations over eastern China in early winter (November–January). Studies show that 65% of the strong EAT evolved from a cyclonic anomaly over Kazakhstan have significant effects on PM 2.5 concentration in the North China Plain. From day −3 to day 0 prior the EAT peak, increased northerly wind and higher planetary boundary layer height caused by the strong EAT enhance atmospheric diffusion conditions, leading to lower PM 2.5 concentration. PM 2.5 concentration tends to decrease on day 4 prior to the peak of EAT events and reaches its minimum on the third day after that. In addition, surface O 3 concentrations in the Yangtze River basin experienced the first decrease and then increase with a turning point at day 1 after the peak of EAT events. These changes in the O 3 concentration are attributed to changes in the surface temperature anomaly and surface downward solar radiation associated with the EAT. Specifically, the EAT-related lower surface temperatures and less downward solar radiation before the peak of the EAT events (i.e., day −4 to day 1) favor lower O 3 concentrations and vice versa after the peak of the EAT (i.e., day 2 to day 4). Our findings could be of great value for the targeted emission reductions in eastern China in early winter. • The strong East Asian trough event has a significant dispersive effect on the wintertime PM 2.5 over the North China Plain. • Surface O 3 in the Yangtze River basin typically first decreases and then increases during the strong East Asian trough. • Changes in surface O3 are driven by anomalous surface air temperatures and solar radiation. [ABSTRACT FROM AUTHOR]

The North China Plain (NCP) is a major region of summer O 3 pollution in China. However, the contribution of stratosphere-to-troposphere transport (STT) to summertime surface O 3 in the NCP and the meteorological mechanisms are poorly understood. In this study, meteorological reanalysis data, O 3 observations, and Lagrange modeling were used to analyze the contribution of the STT to the change in surface O 3 in the NCP, the vertical transport pathways, and the associated meteorological mechanism. In summer 2019, the STT contributed an estimated 5.7%–18.8% to the surface O 3 concentrations in the NCP. The influence of the STT in the NCP is closely related to the changes in westerly circulation in the upper troposphere and lower stratosphere (UTLS) over the Eurasian region. The troughs and vortices in the westerlies led to the convergences of O 3 in the UTLS and tropopause folding, forming downward intrusions of O 3 -rich air from the UTLS to the lower troposphere. Controlled by the westerly circulation, the O 3 source regions of STT in the stratosphere are found between 40° and 70°N, oscillating zonally with changing transport periods, where a key source region of STT is situated steadily over 60°-100°E northwest of the NCP. In association with the cut-off low of westerly circulation in the UTLS over Siberia evolved from the splitting of the polar vortex, a slanted channel of O 3 downward intrusion was set up from the UTLS to the lower troposphere over the NCP in 7 days. As the cut-off low in westerly circulation moves southeastward close to the NCP, the channel of the O 3 downward intrusion is set upright with a shorter period of vertical transport to the NCP ground. Our results provide insights into the the O 3 source–receptor relationship in the STT with vertical O 3 transport structures in changes in the atmospheric environment. • STT contributes 5.7%–18.8% to surface O 3 in the North China Plain (NCP). • Stratospheric O 3 sources intruding NCP oscillate over 60–100°E and 40–70°N. • STT affects NCP with long-range slanted channels followed by upright transport. [ABSTRACT FROM AUTHOR]

Abstract: Surface ozone (O3) measurements were carried out in the marine environment of the Arabian Sea (AS) during the premonsoon months, April–May 2006, as part of the Integrated Campaign for Aerosols, gases and Radiation Budget. The O3 mixing ratio over the AS varied in the range ∼3–22 ppb with a mean of 13.5 ± 2 ppb. Comparatively high mixing ratios were observed over the southern AS and close to the coast. The spatial pattern did not show any evidence of transport from nearby landmass or in situ photochemistry. Longitudinally separated narrow regions of low and high O3 were seen over the southern AS. The role of aerosols in modifying the O3 concentration was examined based on the co-located measurement of aerosol mass loading, number density, size distribution and optical depth. The O3 mixing ratio showed positive correlation with aerosol loading. Over high O3 regions, large particle concentration showed significant enhancement. The role of chloride ion in depleting O3 was also investigated. The observed spatial features were compared with those measured during the earlier cruises conducted in different seasons and over various oceanic regions. A comparison has been made with the measurements over the Bay of Bengal during the same cruise. [Copyright &y& Elsevier]

Abstract: Observations were made of surface O3, NO x , UV radiation, and meteorological parameters at DBR, Guangdong province, and the statistical relationship of O3 to its factors (NO x , water, scattering, UV radiation) was studied. An empirical method was applied to estimate O3. The calculated value agrees well with that observed under different sky conditions, and averaged relative biases of daily O3 concentrations in clear and all sky conditions were ⩽7%. A good correlation was found between O3 and the ratio of NO2/NO in clear and all sky conditions, and correlation coefficients between O3 and NO2/NO were more than 0.90. This empirical method can be used as a tool to analyze the relationship between O3 and the factors affecting it. The analysis shows that O3 is more sensitive to the change of NO and NO2 than that of other factors. [Copyright &y& Elsevier]

The World Health Organization, which proclaimed the COVID-19 a pandemic in early March 2020, imposed a partial lockdown by the Government of India on 21 March 2020. The aim of this investigation was to measure the change in air pollutants, including particulate matter (PM 2.5 and PM 10) and gaseous pollutants (NO 2 , CO and O 3) during COVID-19 lockdown (25th March to 14th April 2020) across four major polluted cities in North India. In all region, PM 2.5 , PM 10 , NO 2 and CO were significantly reduced while O 3 has been shown mixed variation with increased in Agra and decreased in all other stations during lockdown. PM 2.5 was reduced by ~20–50% and highly decreased in Noida. PM 10 was most significantly decreased by 49% in Delhi. NO 2 was reduced by ~10–70%, and high reduction was observed in Noida. Likewise, ~10–60% reduction was found in CO and most significantly decreased in Gurugram. However, an increased in O3 was observed in Agra by 98% while significantly reduced in other sites. Compared to the same timeframe in 2018–2019, PM 2.5 and PM 10 values for all sites were reduced by more than 40%. Unlabelled Image • Effect of Lockdown during COVID-19 on Air quality has been analysed. • The concentration of PM 2.5 and PM 10 were highly declined in Noida and Delhi. • The concentrations of NO 2 and CO were declined in at all observing sites. [ABSTRACT FROM AUTHOR]