Recent changes observed in column ozone concentrations over India

Ozone observations taken during the past 23-39 years by Dobson Spectrophotometers at Delhi, Varanasi, Pune and Kodikanal have been analysed to examine its long-term trend over Indian stations. An increasing trend of this species over the years has been noticed at all the places, except at Varanasi, where a decreasing trend has been found. The cause of these trends could be attributed, partly, to the trends of ozone in the troposphere. The results also indicate that there are certain recent changes in ozone levels at the Indian stations. These changes are less apparent in long-term trend analysis of total ozone data as the increase in tropospheric ozone has a compensating effect to the decrease in ozone at stratospheric levels.

Trends and Variability of Ozone Pollution over the Mountain-Basin Areas in Sichuan Province during 2013–2020: Synoptic Impacts and Formation Regimes

Sichuan Province, the most industrialized and populated region in southwestern China, has been experiencing severe ozone pollution in the boreal warm season (April–September). With a surface ozone monitoring network and reanalysis dataset, we find that nearly all cities in Sichuan Province showed positive increasing trends in the warm-season ozone levels. The warm-season daily maximum 8-h average (MDA8) ozone levels increased by 2.0 ppb (4.8%) year−1 as a whole, with slightly larger trends in some sites such as a site in Zigong (5.2 ppb year−1). Seasonally, the monthly ozone level in Sichuan peaks from May to August (varies with year). The predominant warm-season synoptic patterns were objectively identified based on concurrent hourly meteorological fields from ERA5. High-pressure systems promote ozone production and result in high ozone concentrations, due to strong solar radiation as well as hot and dry atmospheric conditions. The increased occurrence of high-pressure patterns probably drives the ozone increase in Sichuan. When ozone pollution is relatively weak (with MDA8 ozone around 170 μg m−3), the air quality standard could be achieved in the short term by a 25% reduction of NOx and VOCs emissions. Strengthened emission control is needed when ozone pollution is more severe. Our study provides implications for effective emission control of ozone pollution in Sichuan.

Rotating tongues (Protrudences) of ozone- poor air in the Antarctic ozone hole, sweeping over lower latitudes : signatures in ground-based Dobson data

Using data from ground-based Dobson spectrophotometers, the evolution of Antarctic ozone holes during the southern springs of 1992, 1993, 1994 and 1995 was studied, At the South Pole, the evolution was mostly smooth, steady decrease up to about September end and a steady recovery up to about December end, At latitudes near 65°5, the ozone levels at different latitudes and longitudes showed fluctuations compatible with passing of a noncircular (oval) vortex boundary, (edge, rotating tongue), with a rotation period of 15-20 days, However, often there were depletions in-between, extending to lower latitudes up to ~30°S, indicating corrugations in the oval boundary with effects equivalent to those of more than one rotating tongue, There were other short- spaced (5-8 days) depletions, not necessarily simultaneous at different latitudes in the same longitude, and more copious at lower latitudes, probably indicating the effects of synoptic disturbances on total ozone through tropopause pressure changes and/or ozone mini-holes caused by anticyclonic tropospheric forcing under the southern polar vortex.

The Impact of COVID-19 Confinement Measures on the Air Quality in an Urban-Industrial Area of Portugal

This study evaluated the temporal variability of the concentrations of pollutants (namely, NO2, O3, PM2.5, PM10 and SO2) in an urban-industrial area of mainland Portugal during two decades (from 2001 to 2020), to assess the impact of the COVID-19 pandemic on the levels of these atmospheric pollutants. Mean levels of pollutants in 2020 were compared with those measured in the six previous years (2014–2019). A significant improvement in air quality, namely regarding PM10 and NO2, was found and it can be attributable to the restrictions of anthropogenic activities (such as traffic) promoted during the March–May 2020 national lockdown that occurred due to the pandemic. Significant and expressive reductions of 44.0% and 40.3% were found in April 2020 for NO2 and PM10, respectively, showing the impact of local traffic in the study area. A similar trend of reduction for these pollutants was also found in the following months. However, ozone levels did not show the same trend, with significant increases in several months after the lockdown period, highlighting other contributions to this pollutant. This unique period can be considered as a living lab, where the implementation of strict measures due to COVID-19 confinement promoted the reduction of anthropogenic activities and allowed us to understand more comprehensively their impact on local air quality.

Climate Change will Increase Ozone Levels and Unravel Air Quality Regulations

Using daily data for the United States over the period 1980-2019, we estimate the impacts of temperature on ambient ozone concentrations, accounting for adaptation to climatic change. We find that even with adaptation, rises in temperature will steeply increase ozone levels by over 9 ppb on days above 25◦ C. By mid-century, we calculate that 189 additional counties 15 will be violating the air quality standards, with 33 million more residents exposed to unhealthy levels of ozone. Climate change will thus likely increase the costs of compliance with existing ambient ozone standards. In light of a recent EPA ruling that would effectively remove cobenefits of ozone precursor reductions from the cost-benefit analysis of those standards, they will be in peril, further threatening public health.

Climate Change will Increase Ozone Levels and unravel Air Quality Regulations

Using daily data for the United States over the period 1980-2019, we estimate the impacts of temperature on ambient ozone concentrations, accounting for adaptation to climatic change. We find that even with adaptation, rises in temperature will steeply increase ozone levels by over 9 ppb on days above 25◦C. By mid-century, we calculate that 189 additional counties will be violating the air quality standards, with 33 million more residents exposed to unhealthy levels of ozone. Climate change will thus likely increase the costs of compliance with existing ambient ozone standards. In light of a recent EPA ruling that would effectively remove co-benefits of ozone precursor reductions from the cost-benefit analysis of those standards, they will be in peril, further threatening public health.

The impact of Los Angeles Basin pollution and stratospheric intrusions on the surrounding San Gabriel Mountains as seen by surface measurements, lidar, and numerical models

In this work, the impact of Los Angeles Basin pollution transport and stratospheric intrusions on the surface ozone levels observed in the San Gabriel Mountains is investigated based on a combination of surface and lidar measurements as well as WRF-Chem (Weather Research and Forecasting with Chemistry) and WACCM (Whole Atmosphere Community Climate Model) runs. The number of days with observed surface ozone levels exceeding the National Ambient Air Quality Standards exhibit a clear seasonal pattern, with a maximum during summer, when models suggest a minimum influence of stratospheric intrusions and the largest impact from Los Angeles Basin pollution transport. Additionally, measured and modeled surface ozone and PM10 were analyzed as a function of season, time of the day, and wind direction. Measurements and models are in good qualitative agreement, with maximum surface ozone observed for southwest and west winds. For the prevailing summer wind direction, slightly south of the ozone maximum and corresponding to south-southwest winds, lower ozone levels were observed. Back trajectories suggest that this is associated with transport from the central Los Angeles Basin, where titration limits the amount of surface ozone. A quantitative comparison of the lidar profiles with WRF-Chem and WACCM models revealed good agreement near the surface, with models showing an increasing positive bias as function of altitude, reaching 75 % at 15 km above sea level. Finally, three selected case studies covering the different mechanisms affecting the near-surface ozone concentration over the San Gabriel Mountains, namely stratospheric intrusions and pollution transport, are analyzed based on surface and ozone lidar measurements, as well as co-located ceilometer measurements and models.