Ozone Reduction Research Articles

MAX-DOAS and in-situ measurements of aerosols and trace gases over Dongying, China: Insight into ozone formation sensitivity based on secondary HCHO

This study presents a comprehensive overview of the atmospheric pollutants including Sulfur dioxide (SO2), Nitrogen dioxide (NO2), Formaldehyde (HCHO), Particulate Matter PM; PM10: diameter ≤ 10 µm, and PM2.5: diameter ≤ 2.5 µm), and Ozone (O3), over Dongying (Shandong Province) from March-April 2018 and September-October 2019 by employing ground-based Multiple Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) observations along with the in-situ measurements attained by the national air quality monitoring platform. The concentrations of SO2 and NO2 were under the acceptable level, while both PM2.5, and PM10 were higher than the safe levels as prescribed by national and international air quality standards. The results depict that 21% of the total observation days were found to be complex polluted days (PM2.5 > 35 µg/m3 and O3 > 160 µg/m3). The secondary HCHO was used for accurate analysis of O3 sensitivity. A difference of 11.40% and 10% during March-April 2018 and September-October 2019 respectively in O3 sensitivity was found between HCHOtotal/NO2 and HCHOsec/NO2. The results indicate that primary HCHO have significant contribution in HCHO. O3 formation predominantly remained to be in VOC-limited and transitional regime during March-April 2018 and September-October 2019 in Dongying. These results imply that concurrent control of both NOx and VOCs would benefit in ozone reductions. Additionally, the criteria pollutants (PM, SO2, and NO2) depicted strong correlations with each other except for O3 for which weak correlation coefficient was obtained with all the species. This study will prove to be baseline for designing of air pollution control strategies.

Ozone depletion in the Arctic and Antarctic stratosphere induced by wildfire smoke

Abstract. A record-breaking stratospheric ozone loss was observed over the Arctic and Antarctica in 2020. Strong ozone depletion occurred over Antarctica in 2021 as well. The ozone holes developed in smoke-polluted air. In this article, the impact of Siberian and Australian wildfire smoke (dominated by organic aerosol) on the extraordinarily strong ozone reduction is discussed. The study is based on aerosol lidar observations in the North Pole region (October 2019–May 2020) and over Punta Arenas in southern Chile at 53.2∘ S (January 2020–November 2021) as well as on respective NDACC (Network for the Detection of Atmospheric Composition Change) ozone profile observations in the Arctic (Ny-Ålesund) and Antarctica (Neumayer and South Pole stations) in 2020 and 2021. We present a conceptual approach on how the smoke may have influenced the formation of polar stratospheric clouds (PSCs), which are of key importance in the ozone-depleting processes. The main results are as follows: (a) the direct impact of wildfire smoke below the PSC height range (at 10–12 km) on ozone reduction seems to be similar to well-known volcanic sulfate aerosol effects. At heights of 10–12 km, smoke particle surface area (SA) concentrations of 5–7 µm2 cm−3 (Antarctica, spring 2021) and 6–10 µm2 cm−3 (Arctic, spring 2020) were correlated with an ozone reduction in terms of ozone partial pressure of 0.4–1.2 mPa (about 30 % further ozone reduction over Antarctica) and of 2–3.5 mPa (Arctic, 20 %–30 % reduction with respect to the long-term springtime mean). (b) Within the PSC height range, we found indications that smoke was able to slightly increase the PSC particle number and surface area concentration. In particular, a smoke-related additional ozone loss of 1–2 mPa (10 %–20 % contribution to the total ozone loss over Antarctica) was observed in the 14–23 km PSC height range in September–October 2020 and 2021. Smoke particle number concentrations ranged from 10 to 100 cm−3 and were about a factor of 10 (in 2020) and 5 (in 2021) above the stratospheric aerosol background level. Satellite observations indicated an additional mean column ozone loss (deviation from the long-term mean) of 26–30 Dobson units (9 %–10 %, September 2020, 2021) and 52–57 Dobson units (17 %–20 %, October 2020, 2021) in the smoke-polluted latitudinal Antarctic belt from 70–80∘ S.

Enhancing hydroxyl radical production from cathodic ozone reduction during the ozone-electrolysis process with flow-through reactive electrochemical membrane cathode.

In this study, a flow-through ozone-electrolysis (O3-electrolysis) process was developed by combining ozonation with an electrolysis using a porous reactive electrochemical membrane (REM) cathode. Due to the convection-enhanced mass transport and fast radial diffusion inside the small pores of REM cathodes, the rate of cathodic O3 reduction to ozonide radicals (O3•-) was significantly enhanced, while the further cathodic O3•- reduction to oxygen was inhibited during the flow-through O3-electrolysis process compared to the conventional mixed-tank O3-electrolysis process. Consequently, more hydroxyl radicals (•OH) were formed from O3•- decay in water during the flow-through O3-electrolysis process than the mixed-tank O3-electrolysis process. Corresponding to the higher •OH yields from cathodic O3 reduction, the flow-through O3-electrolysis process substantially enhanced the abatement kinetics and efficiency of para-benzoic acid (pCBA, a model compound of ozone-resistant micropollutant) in a groundwater than conventional ozonation and the mixed-tank O3-electrolysis process. These results suggest that the flow-through O3-electrolysis process may provide a competitive treatment technology for micropollutant abatement in water treatment.

US Clean Energy Futures—Air Quality Benefits of Zero Carbon Energy Policies

In this work, we compare the air quality benefits of a variety of future policy scenarios geared towards controlling EGU (electricity generating units) emissions between the present-day conditions and 2050. While these policies are motivated by reducing CO2 emissions, they also yield significant co-benefits for criteria pollutants, such as ozone and PM2.5. An integrated set of clean energy policies were examined to assess the time-varying costs and benefits of a range of decarbonization strategies, including business as usual and the Affordable Clean Energy plan, with a primary focus on others that look to achieve very low, if not zero, CO2 emissions from the EGU sector by 2050. Benefits assessed include mitigation of greenhouse gas emissions as well as air quality co-benefits. In this introductory work, we describe the potential air quality changes from various clean air policies, to set the stage for upcoming work looking at health and monetized benefits. Emission changes for key pollutants are forecast using the Integrated Planning Model (IPM), which are then transformed into emission inputs for the Community Multiscale Air Quality Model (CMAQ). For all primary scenarios considered that achieve large greenhouse gas decreases, significant reductions in ozone and PM are realized, mainly in the eastern US, and all policies produce air quality benefits.

Seasonal Variation Characteristics of VOCs and Their Influences on Secondary Pollutants in Yibin, Southwest China

Volatile organic compounds (VOCs) have a crucial impact on the formation of ozone and secondary organic aerosols in the near-surface atmosphere. Understanding the composition characteristics and sources of VOCs is necessary for determining effective control policies to mitigate VOCs and related secondary pollutions. We performed on-line measurements of VOC species in typical months of each season in Yibin, a fast-growing city in Sichuan Basin in China, to identify VOC seasonal characteristics, sources, and the potential for secondary pollution formation. The average mixing ratio of VOCs in Yibin was 22.3 ppbv. Five major emission sources were identified through the positive matrix factorization model, namely, gasoline vehicle, diesel vehicle, industrial manufacturing, solvent utilization, regional background, and secondary formation. Aromatics and alkenes played leading roles in the secondary formation of ozone and secondary organic aerosols. Furthermore, m/p-xylene, ethylene, and toluene were identified to be the major reactive species. Future management should consider targeting these compounds when evaluating ozone and aerosol reduction strategies. Vehicle and solvent utilization emission mitigation would be the primary and effective ways to improve air quality in the fast-developing city in this region.

Impacts of replacing coal with renewable energy sources and electrifying the transportation sector on future ozone concentrations in the U.S. under a warming climate

The potential impacts of emission reduction strategies in the electric power and transportation sectors on future ozone concentrations in the U.S. are investigated. A modeling system consisting of: the Weather Research and Forecasting (WRF), the Community Earth System Model (CESM), the GEOS-Chem, and the Comprehensive Air Quality Model with Extensions (CAMx) is deployed under a climate change scenario to simulate ozone pollution changes by mid-century. In addition to the control case, which represents current conditions, two emission reduction cases are simulated. The first (CASE1) includes the effects of decommissioning older coal-fired power plants and supplying their electricity with a mix of renewable sources and natural gas power plants. The second emission reduction case (CASE2) includes the effects of electrifying mobile sources. In CASE2, the emission reductions in the power sector remain the same as in CASE1, but further emission reductions result from an increase in electric vehicles, powered by renewable electricity and a small increase in natural gas for reserves. Results show that, for CASE1, ozone levels decrease modestly, with the maximum ozone benefit (−-0.7 ppb) in the U.S. Central region, where the most coal decommissions take place. In CASE2, ozone levels decrease significantly everywhere with maximum decreases of −3.7 ppb and −3.5 ppb in the North East and South East regions, respectively. The study indicates that, in the summer, coal-fired power plant decommissioning would have only local and modest ozone benefits, whereas mobile source electrification could help achieve larger ozone reduction goals at the regional scale.

NASA Satellite Measurements Show Global-Scale Reductions in Free Tropospheric Ozone in 2020 and Again in 2021 During COVID-19.

NASA satellite measurements show that ozone reductions throughout the Northern Hemisphere (NH) free troposphere reported for spring‐summer 2020 during the COronaVIrus Disease 2019 pandemic have occurred again in spring‐summer 2021. The satellite measurements show that tropospheric column ozone (TCO) (mostly representative of the free troposphere) for 20°N–60°N during spring‐summer for both 2020 and 2021 averaged ∼3 Dobson Units (DU) (or ∼7%–8%) below normal. These ozone reductions in 2020 and 2021 were the lowest in the 2005–2021 record. We also include satellite measurements of tropospheric NO2 that exhibit reductions of ∼10%–20% in the NH in early spring‐to‐summer 2020 and 2021, suggesting that reduced pollution was the main cause for the low anomalies in NH TCO in 2020 and 2021. Reductions of TCO ∼2 DU (7%) are also measured in the Southern Hemisphere in austral summer but are not associated with reduced NO2.

Ionic Wind Intensity Enhancement and Ozone Reduction in a Solid-State Fan Via Electromagnetic Field Action

Ionic Wind Intensity Enhancement and Ozone Reduction in a Solid-State Fan Via Electromagnetic Field Action

Observation-based analysis of ozone production sensitivity for two persistent ozone episodes in Guangdong, China

Abstract. An observation-based method (OBM) is developed to investigate the sensitivity of ozone formation to precursors during two persistent elevated ozone episodes observed at 77 stations in Guangdong. Average OH concentrations derived at the 77 stations between 08:00 and 13:00 local time stay within a narrow range of 2.5×106 to 5.5×106 cm−3 with a weak dependence on the NOx. These values are in good agreement with OH values observed at a rural station in the Pearl River Delta (PRD). They also agree well with a box model constrained by the ambient conditions observed during the two episodes. The OBM has been used to evaluate the ozone production efficiency, ε(NOx or volatile organic compound, VOC), defined as the number of O3 molecules produced per molecule of NOx (or VOC) oxidized. Average values of ε(NOx) and ε(VOC) determined by the OBM are 3.0 and 2.1 ppb ppb−1, respectively, and both compared well with values in previous studies. Approximately 67 % of the station days exhibit ozone formation sensitivity to NOx, and approximately 20 % of the station days are in the transitional regime sensitive to both NOx and VOC, and only approximately 13 % of the station days are sensitive to VOC. These results are in semi-quantitative agreement with the ozone formation sensitivity calculated by the box model constrained by ambient conditions observed during the two episodes. However, our OBM results differ from those of most previous investigations, which suggested that limiting the emission of VOC rather than NOx would be more effective in reducing ozone reduction in Guangdong.

Air quality improvements are projected to weaken the Atlantic meridional overturning circulation through radiative forcing effects

Observations indicate the Atlantic Meridional Overturning Circulation-a fundamental component of the ocean’s global conveyor belt-is weakening. Although causes remain uncertain, such weakening is consistent with increasing greenhouse gases. Recent studies also suggest that anthropogenic emissions associated with air pollution can impact the Atlantic Meridional Overturning Circulation. Here, we use four state-of-the-art chemistry-climate models to quantify how efforts to improve future air quality, via near-term climate forcer mitigation, will impact the Atlantic Meridional Overturning Circulation. Future reductions in aerosols, ozone and precursor gases alone induces end-of-century weakening of the Atlantic Meridional Overturning Circulation by up to 10%. However, when methane reductions are also included, this weakening is offset. The responses are best explained by changes in the North Atlantic radiative forcing. Thus, efforts to improve air quality must also target methane and other greenhouse gases including carbon dioxide to avoid weakening of the world’s major ocean circulation system.

The Climate and Ozone Impacts of Black Carbon Emissions From Global Rocket Launches

AbstractAerosol emissions from spaceflight activities play a small but increasing role in the background stratospheric aerosol population. Rockets used by the global launch industry emit black carbon (BC) particles directly into the stratosphere where they accumulate, absorb solar radiation, and warm the surrounding air. We model the chemical and dynamical response of the atmosphere to northern mid‐latitude rocket BC emissions. We initially examine emissions at a rate of 10 Gg per year, which is an order of magnitude larger than current emissions, but consistent with extrapolations of space traffic growth several decades into the future. We also perform runs at 30 and 100 Gg per year in order to better delineate the atmosphere's response to rocket BC emissions. We show that a 10 Gg/yr rocket BC emission increases stratospheric temperatures by as much as 1.5 K in the stratosphere. Changes in global circulation also occur. For example, the annual subtropical jet wind speeds slow down by as much as 5 m/s, while a 10%–20% weakening of the overturning circulation occurs in the northern hemisphere during multiple seasons. Warming temperatures lead to a ozone reduction in the northern hemisphere by as much as 16 DU in some months. The climate response increases in a near linear fashion when looking at larger 30 and 100 Gg emission scenarios. Comparing the amplitude of the atmospheric response using different emission rates provides insight into stratospheric adjustment and feedback mechanisms. Our results show that the stratosphere is sensitive to relatively modest BC injections.

Australian wildfire smoke in the stratosphere: the decay phase in 2020/2021 and impact on ozone depletion

Abstract. Record-breaking wildfires raged in southeastern Australia in late December 2019 and early January 2020. Rather strong pyrocumulonimbus (pyroCb) convection developed over the fire areas and lofted enormous amounts of biomass burning smoke into the tropopause region and caused the strongest wildfire-related stratospheric aerosol perturbation ever observed around the globe. We discuss the geometrical, optical, and microphysical properties of the stratospheric smoke layers and the decay of this major stratospheric perturbation. A multiwavelength polarization Raman lidar at Punta Arenas (53.2∘ S, 70.9∘ W), southern Chile, and an elastic backscatter Raman lidar at Río Grande (53.8∘ S, 67.7∘ W) in southern Argentina, were operated to monitor the major record-breaking event until the end of 2021. These lidar measurements can be regarded as representative for mid to high latitudes in the Southern Hemisphere. A unique dynamical feature, an anticyclonic, smoke-filled vortex with 1000 km horizontal width and 5 km vertical extent, which ascended by about 500 m d−1, was observed over the full last week of January 2020. The key results of the long-term study are as follows. The smoke layers extended, on average, from 9 to 24 km in height. The smoke partly ascended to more than 30 km height as a result of self-lofting processes. Clear signs of a smoke impact on the record-breaking ozone hole over Antarctica in September–November 2020 were found. A slow decay of the stratospheric perturbation detected by means of the 532 nm aerosol optical thickness (AOT) yielded an e-folding decay time of 19–20 months. The maximum smoke AOT was around 1.0 over Punta Arenas in January 2020 and thus 2 to 3 orders of magnitude above the stratospheric aerosol background of 0.005. After 2 months with strongly varying smoke conditions, the 532 nm AOT decreased to 0.03-0.06 from March–December 2020 and to 0.015–0.03 throughout 2021. The particle extinction coefficients at 532 nm were in the range of 10–75 Mm−1 in January 2020 and, later on, mostly between 1 and 5 Mm−1. Combined lidar–photometer retrievals revealed typical smoke extinction-to-backscatter ratios of 69 ± 19 sr (at 355 nm), 91 ± 17 sr (at 532 nm), and 120 ± 22 sr (at 1064 nm). An ozone reduction of 20 %–25 % in the 15–22 km height range was observed over Antarctica and New Zealand ozonesonde stations in the smoke-polluted air, with particle surface area concentrations of 1–5 µm2 cm−3.

The sensitivities of ozone and PM2.5 concentrations to the satellite-derived leaf area index over East Asia and its neighboring seas in the WRF-CMAQ modeling system

Vegetation plays an important role as both a sink of air pollutants via dry deposition and a source of biogenic VOC (BVOC) emissions which often provide the precursors of air pollutants. To identify the vegetation-driven offset between the deposition and formation of air pollutants, this study examines the responses of ozone and PM2.5 concentrations to changes in the leaf area index (LAI) over East Asia and its neighboring seas, using up-to-date satellite-derived LAI and green vegetation fraction (GVF) products. Two LAI scenarios that examine (1) table-prescribed LAI and GVF from 1992 to 1993 AVHRR and 2001 MODIS products and (2) reprocessed 2019 MODIS LAI and 2019 VIIRS GVF products were used in WRF-CMAQ modeling to simulate ozone and PM2.5 concentrations for June 2019. The use of up-to-date LAI and GVF products resulted in monthly mean LAI differences ranging from −56.20% to 96.81% over the study domain. The increase in LAI resulted in the differences in hourly mean ozone and PM2.5 concentrations over inland areas ranging from 0.27 ppbV to −7.17 ppbV and 0.89 μg/m3 to −2.65 μg/m3, and the differences of those over the adjacent sea surface ranging from 0.69 ppbV to −2.86 ppbV and 3.41 μg/m3 to −7.47 μg/m3. The decreases in inland ozone and PM2.5 concentrations were mainly the results of dry deposition accelerated by increases in LAI, which outweighed the ozone and PM2.5 formations via BVOC-driven chemistry. Some inland regions showed further decreases in PM2.5 concentrations due to reduced reactions of PM2.5 precursors with hydroxyl radicals depleted by BVOCs. The reductions in sea surface ozone and PM2.5 concentrations were accompanied by the reductions in those in upwind inland regions, which led to less ozone and PM2.5 inflows. The results suggest the importance of the selective use of vegetation parameters for air quality modeling.

Mitigation of air pollutant impacts on rice yields in China by sector

Air quality management is a complex project involving the coordination of multiple sectors and has been identified as an important strategy for food security. However, little is known about how pollutant emissions from each sector affect agriculture. Each sector emits different precursors, resulting in varying impacts of their pollutants and aerosol-climate on rice yield. Therefore, we provide an assessment of air pollution impacts, including direct ozone damage and aerosol-climate effects, on rice yield in four sector (industrial, energy, domestic, and transportation) emission scenarios in China. Our results suggest that without anthropogenic emissions, a reduced surface ozone concentration leads to a 9.8% increase in rice yield; lower aerosol concentrations induce an additional 2.3% increase, leading to a combined 9.7% greater rice yield. Of the four sectors, industrial sector emission control is projected to be the most effective, with 4.4% rice yield gain from ozone reductions and 0.6% from aerosol reductions. The impacts of the energy and transportation sectors are relatively low, resulting in 2.1% (energy sector) and 0.7% (transportation) yield increases on average. The domestic sector has few emissions of ozone precursors; therefore, aerosol-climate effects are more dominant, resulting in a yield increase of 0.9%. These results indicate the importance of reduced emissions in the industrial sector for future agricultural food production while also providing the relative benefits of regulating each sector for food security.

Stratospheric ozone response to sulfate aerosol and solar dimming climate interventions based on the G6 Geoengineering Model Intercomparison Project (GeoMIP) simulations

Abstract. This study assesses the impacts of stratospheric aerosol intervention (SAI) and solar dimming on stratospheric ozone based on the G6 Geoengineering Model Intercomparison Project (GeoMIP) experiments, called G6sulfur and G6solar. For G6sulfur, an enhanced stratospheric sulfate aerosol burden reflects some of the incoming solar radiation back into space to cool the surface climate, while for G6solar, the reduction in the global solar constant in the model achieves the same goal. Both experiments use the high emissions scenario of SSP5-8.5 as the baseline experiment and define surface temperature from the medium emission scenario of SSP2-4.5 as the target. In total, six Earth system models (ESMs) performed these experiments, and three out of the six models include interactive stratospheric chemistry. The increase in absorbing sulfate aerosols in the stratosphere results in a heating of the lower tropical stratospheric temperatures by between 5 to 13 K for the six different ESMs, leading to changes in stratospheric transport, water vapor, and other related changes. The increase in the aerosol burden also increases aerosol surface area density, which is important for heterogeneous chemical reactions. The resulting changes in the springtime Antarctic ozone between the G6sulfur and SSP5-8.5, based on the three models with interactive chemistry, include an initial reduction in total column ozone (TCO) of 10 DU (ranging between 0–30 DU for the three models) and up to 20 DU (between 10–40 DU) by the end of the century. The relatively small reduction in TCO for the multi-model mean in the first 2 decades results from variations in the required sulfur injections in the models and differences in the complexity of the chemistry schemes. In contrast, in the Northern Hemisphere (NH) high latitudes, no significant changes can be identified due to the large natural variability in the models, with little change in TCO by the end of the century. However, all three models with interactive chemistry consistently simulate an increase in TCO in the NH mid-latitudes up to 20 DU, compared to SSP5-8.5, in addition to the 20 DU increase resulting from increasing greenhouse gases between SSP2-4.5 and SSP5-8.5. In contrast to G6sulfur, G6solar does not significantly change stratospheric temperatures compared to the baseline simulation. Solar dimming results in little change in TCO compared to SSP5-8.5. Only in the tropics does G6solar result in an increase of TCO of up to 8 DU, compared to SSP2-4.5, which may counteract the projected reduction in SSP5-8.5. This work identifies differences in the response of SAI and solar dimming on ozone for three ESMs with interactive chemistry, which are partly due to the differences and shortcomings in the complexity of aerosol microphysics, chemistry, and the description of ozone photolysis. It also identifies that solar dimming, if viewed as an analog to SAI using a predominantly scattering aerosol, would succeed in reducing tropospheric and surface temperatures, but any stratospheric changes due to the high forcing greenhouse gas scenario, including the potential harmful increase in TCO beyond historical values, would prevail.

Ozone pollution during the COVID-19 lockdown in the spring of 2020 over Europe, analysed from satellite observations, in situ measurements, and models

Abstract. We present a comprehensive study integrating satellite observations of ozone pollution, in situ measurements, and chemistry-transport model simulations for quantifying the role of anthropogenic emission reductions during the COVID-19 lockdown in spring 2020 over Europe. Satellite observations are derived from the IASI+GOME2 (Infrared Atmospheric Sounding Interferometer + Global Ozone Monitoring Experiment 2) multispectral synergism, which provides better sensitivity to near-surface ozone pollution. These observations are mainly analysed in terms of differences between the average on 1–15 April 2020, when the strictest lockdown restrictions took place, and the same period in 2019. They show clear enhancements of near-surface ozone in central Europe and northern Italy, as well as some other hotspots, which are typically characterized by volatile organic compound (VOC)-limited chemical regimes. An overall reduction of ozone is observed elsewhere, where ozone chemistry is limited by the abundance of NOx. The spatial distribution of positive and negative ozone concentration anomalies observed from space is in relatively good quantitative agreement with surface in situ measurements over the continent (a correlation coefficient of 0.55, a root-mean-squared difference of 11 ppb, and the same standard deviation and range of variability). An average difference of ∼ 8 ppb between the two observational datasets is observed, which can partly be explained by the fact the satellite approach retrieves partial columns of ozone with a peak sensitivity above the surface (near 2 km of altitude over land and averaging kernels reaching the middle troposphere over ocean). For assessing the impact of the reduction of anthropogenic emissions during the lockdown, we adjust the satellite and in situ surface observations for subtracting the influence of meteorological conditions in 2020 and 2019. This adjustment is derived from the chemistry-transport model simulations using the meteorological fields of each year and identical emission inventories. Using adjustments adapted for the altitude and sensitivity of each observation, both datasets show consistent estimates of the influence of lockdown emission reduction. They both show lockdown-associated ozone enhancements in hotspots over central Europe and northern Italy, with a reduced amplitude with respect to the total changes observed between the 2 years and an overall reduction elsewhere over Europe and the ocean. Satellite observations additionally provide the ozone anomalies in the regions remote from in situ sensors, an enhancement over the Mediterranean likely associated with maritime traffic emissions, and a marked large-scale reduction of ozone elsewhere over ocean (particularly over the North Sea), in consistency with previous assessments done with ozone sonde measurements in the free troposphere. These observational assessments are compared with model-only estimations, using the CHIMERE chemistry-transport model. Whereas a general qualitative consistency of positive and negative ozone anomalies is observed with respect to observational estimates, significant changes are seen in their amplitudes. Models underestimate the range of variability of the ozone changes by at least a factor 2 with respect to the two observational datasets, both for enhancements and decreases of ozone. Moreover, a significant ozone decrease observed at a large hemispheric scale is not simulated since the modelling domain is the European continent. As simulations only consider the troposphere, the influence from stratospheric ozone is also missing. Sensitivity analyses also show an important role of vertical mixing of atmospheric constituents, which depends on the meteorological fields used in the simulation and significantly modify the amplitude of the changes of ozone pollution during the lockdown.

Smart Dielectric Barrier Discharge Plasma Decontamination: Spatially Targeted Decontamination With Actuated Ozone Distribution

This study introduces spatially targeted decontamination using a synergistic combination of dielectric barrier discharge (DBD) flow actuation and ozone generation. Here, we relate the spatial distribution of local microbial decontaminations in an enclosure to that of local ozone concentrations caused by DBD ozone generation and flow actuation using two reactors with contrasting flow actuation, the Fan and Comb reactors, run at equal power of 1 ± 0.03 W for 3.5 min. Deviations in ozone concentrations and reductions of Escherichia coli on contaminated coupons over two planes were used to quantify the utilization capacity of the generated ozone to simultaneously disinfect regions of a surface placed in the planes. Results show that uniform ozone consumption by a contaminated target, i.e., targeted decontamination, lowers ozone requirements, exposure times, and reactor energy consumption for its disinfection. Furthermore, a significant positive correlation was found between local decontamination and ozone concentrations with Pearson’s correlation, ρ (34) = 0.64; p < 0.001. Simulated ozone distribution using an experiment integrated simulation method, governed by DBD reactor geometry induced flow actuation and ozone reaction rates, is also presented for predicting DBD actuated spatial decontamination distribution. Our study shows an innovative approach of applying DBD plasma reactors for decontamination using flow actuation and ozone generation to achieve targeted killing with maximized ozone utilization lowering overall ozone dosage requirements, energy requirements, and exposure times.

Insights on In-Situ Photochemistry Associated with Ozone Reduction in Guangzhou during the COVID-19 Lockdown

Increases in ground-level ozone (O3) have been observed during the COVID-19 lockdown in many places around the world, primarily due to the uncoordinated emission reductions of O3 precursors. In Guangzhou, the capital of Guangdong province in South China, O3 distinctively decreased during the lockdown. Such a phenomenon was attributed to meteorological variations and weakening of local O3 formation, as indicated by chemical transport models. However, the emission-based modellings were not fully validated by observations, especially for volatile organic compounds (VOCs). In this study, we analyzed the changes of O3 and its precursors, including VOCs, from the pre-lockdown (Pre-LD) to lockdown period (LD) spanning 1 week in Guangzhou. An observation-based box model was applied to understand the evolution of in-situ photochemistry. Indeed, the ambient concentrations of O3 precursors decreased significantly in the LD. A reduction of 20.7% was identified for the total mixing ratios of VOCs, and the transportation-related species experienced the biggest declines. However, the reduction of O3 precursors would not lead to a decrease of in-situ O3 production if the meteorology did not change between the Pre-LD and LD periods. Sensitivity tests indicated that O3 formation was limited by VOCs in both periods. The lower temperature and photolysis frequencies in the LD reversed the increase of O3 that would be caused by the emission reductions otherwise. This study reiterates the fact that O3 abatement requires coordinated control strategies, even if the emissions of O3 precursors can be significantly reduced in the short term.

Characterizing the distinct modulation of future emissions on summer ozone concentrations between urban and rural areas over China

Previous studies on ozone pollution primarily focus on the characterization of ozone on a large regional scale, yet much less attention has been paid towards the contrast between urban and surrounding suburban-rural areas. As anthropogenic emissions are projected to decrease in the coming decades, the evolutions of ozone concentrations over urban and suburban-rural areas are compared using the Community Multiscale Air Quality (CMAQ) model coupled with the Weather Research and Forecasting (WRF). The top 25 city clusters are firstly identified across China based on the amount of NOx emissions and population size. At present, the averages of maximum daily 8-h (MDA8) ozone concentrations over the suburban-rural areas (65.74 ppbv) among these city clusters are higher than the corresponding urban areas (62.00 ppbv). The projections in 2050s depend on the scenarios. Under the Shared Socioeconomic Pathways (SSPs) scenarios such as SSP1-2.6, SSP2-4.5 and SSP5-8.5 indicative of primary decreases in anthropogenic emissions, the mean MDA8 ozone concentrations in suburban-rural areas decrease more than urban areas. In contrast, the gap of higher MDA8 ozone concentrations in suburban-rural than urban areas increases under SSP3-7.0 concomitant with increase in anthropogenic emissions. The strongest response to emission changes is found in SSP1-2.6, in which anthropogenic emission reduction leads to lower MDA8 ozone concentrations in the suburban-rural than urban areas, reversing the present state of higher ozone concentrations in the suburban-rural areas. The feature abovementioned regarding changes of mean MDA8 ozone concentrations is largely reproduced in the response of ozone exceedance. The finding highlights different efficacies of anthropogenic emissions in urban from suburban-rural areas. In a region like China where the population density is much higher in urban than suburban-rural regions, the benefit of ozone reduction due to large emission reductions (e.g., SSP1-2.6) is diminished to some extent because the effect is larger in suburban-rural areas.

Ozone and Particulate Matter Variations in Southwest Ohio, USA, during the COVID-19 Pandemic in 2020

In this study, ozone and particulate matter variations from four monitoring stations in the Southwest Ohio region were analyzed at different stages of the COVID-19 pandemic in 2020, and compared with those in 2019. These stations include a US EPA NCore site (Taft), an urban-suburban site (Sycamore), an industrial source site (Yankee) and a residential site near the source (Amanda). The air quality data were broken down to the lockdown period (March 23 to May 31) and the re-opening periods from June to December, 2020. Publicly available monitoring data on PM2.5, ozone and PM10 were used for analysis. PM2.5 reductions were non-uniform with strong seasonal variations. PM2.5 reductions were 4.04%, 15.6%, 11.63% at Sycamore, Taft and Yankee sites respectively during the lockdown, but increased 11.23% at Amanda. Reductions at Taft may be related to traffic restrictions while those at Yankee may be due to both reduced industrial production and source control measures. Ozone reductions were 7.94% and 6.50% at Sycamore and Taft sites during the lockdown with Sycamore having higher ozone concentrations pre, during and post lockdown. Ozone formation is NOx-limited in Southwest Ohio region and the variations are uniform. Lower temperatures during the lockdown and fall of 2020 can also be a contributing factor. The Air Quality Index (AQI) of combined ozone and PM2.5 improved during the pandemic year. Consistent with a few other studies, COVID-19 restrictions did not bring uniform pollutant reductions to the Southwest Ohio region.