Changes In Tropospheric Ozone Research Articles

Changes in tropospheric ozone over India: Variability, long-term trends and climate forcing

At higher concentrations, tropospheric ozone can cause respiratory difficulties, premature human mortality and can harm vegetation by reducing photosynthesis and its growth. It is an oxidant and also an important greenhouse gas with positive feedback to temperature. It is produced as a byproduct of chemical reactions involving nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the presence of sunlight, rather than being emitted directly to the atmosphere. Here, we analyse the seasonal and inter-annual variability, long-term trends and radiative forcing of the tropospheric column ozone (TPO) in India for the period of 2005–2020 using satellite and ground-based data. The analysis shows very high annual averaged TPO in the Indo-Gangetic Plain (IGP) and North West India, about 45–50 DU. Our findings reveal a significant increase of TPO in India, with the highest trend in the peninsular region (0.295 ± 0.0617 DU/year) and the lowest in North West (0.179 ± 0.048 DU/year). The increase in tropospheric ozone reveals a warming of about 0.5 °C in the troposphere as there is an associated radiative forcing of about 0.2–0.5 W/m2 at the tropopause (125 hPa); indicating that the increasing tropospheric ozone is a great concern for regional warming, public health and ecosystem dynamics.

Seasonal, interannual and decadal variability of tropospheric ozone in the North Atlantic: comparison of UM-UKCA and remote sensing observations for 2005–2018

Abstract. Tropospheric ozone is an important component of the Earth system as it can affect both climate and air quality. In this work, we use observed tropospheric column ozone derived from the Ozone Monitoring Instrument (OMI) and Microwave Limb Sounder (MLS) OMI-MLS, in addition to OMI ozone retrieved in discrete vertical layers, and compare it to tropospheric ozone from UM-UKCA simulations (which utilize the Unified Model, UM, coupled to UK Chemistry and Aerosol, UKCA). Our aim is to investigate recent changes (2005–2018) in tropospheric ozone in the North Atlantic region, specifically its seasonal, interannual and decadal variability, and to understand what factors are driving such changes. The model exhibits a large positive bias (greater than 5 DU or ∼ 50 %) in the tropical upper troposphere: through sensitivity experiments, time series correlation, and comparison with the Lightning Imaging Sensor and Optical Transient Detector lightning flash dataset, the model positive bias in the tropics is attributed to shortcomings in the convection and lightning parameterizations, which overestimate lightning flashes in the tropics relative to mid-latitudes. Use of OMI data, for which vertical averaging kernels and a priori information are available, suggests that the model negative bias (6–10 DU or ∼ 20 %) at mid-latitudes, relative to OMI-MLS tropospheric column, could be the result of vertical sampling. Ozone in the North Atlantic peaks in spring and early summer, with generally good agreement between the modelled and observed seasonal cycle. Recent trends in tropospheric ozone were investigated: whilst both observational datasets indicate positive trends of ∼ 5 % and ∼ 10 % in North Atlantic ozone, the modelled ozone trends are much closer to zero and have large uncertainties. North Atlantic ozone interannual variability (IAV) in the model was found to be correlated to the IAV of ozone transported to the North Atlantic from the stratosphere (R=0.77) and emission of NOx from lightning in the tropics (R=0.72). The discrepancy between modelled and observed trends for 2005–2018 could be linked to the model underestimating lower stratospheric ozone trends and associated stratosphere to troposphere transport. Modelled tropospheric ozone IAV is driven by IAV of tropical emissions of NOx from lightning and IAV of ozone transport from the stratosphere; however, the modelled and observed IAV differ. To understand the IAV discrepancy we investigated how modelled ozone and its drivers respond to large-scale modes of variability. Using OMI height-resolved data and model idealized tracers, we were able to identify stratospheric transport of ozone into the troposphere as the main driver of the dynamical response of North Atlantic ozone to the Arctic Oscillation (AO) and the North Atlantic Oscillation (NAO). Finally, we found that the modelled ozone IAV is too strongly correlated to the El Niño–Southern Oscillation (ENSO) compared to observed ozone IAV. This is again linked to shortcomings in the lightning flashes parameterization, which underestimates (overestimates) lightning flash production in the tropics during positive (negative) ENSO events.

Change in Tropospheric Ozone in the Recent Decades and Its Contribution to Global Total Ozone

AbstractTropospheric ozone is a key chemically active trace gas and radiative forcer. Understanding its long‐term changes is important to properly interpret observed changes in total column ozone and stratospheric ozone recovery. We investigate global and regional tropospheric ozone changes and their impact on total column ozone during 2005–2018 using satellite measurements and the NASA Goddard Earth Observing System Chemistry Climate Model (GEOSCCM). Global total ozone increased ∼4 DU during 2005–2018 (+0.28 ± 0.06 DU yr−1) as inferred from Ozone Monitoring Instrument (OMI). Consistent with previous studies, the OMI/MLS (Microwave Limb Sounder) derived global tropospheric ozone increased 2.2 DU during this period, 60% of the global total column ozone increase. While GEOSCCM reproduces reasonably well the total column increase, it overestimates the stratospheric ozone increase and underestimates the tropospheric ozone increase. We find that the tropospheric ozone increases are likely attributed to a growth of regional emissions of key ozone precursors, especially volatile organic compounds as reflected by the positive trends in formaldehyde (CH2O). Although carbon monoxide (CO) has been decreasing everywhere around the globe, it has relatively small impact on the tropospheric ozone trend. Trends in nitrogen dioxide (NO2) vary with regions, and these changes counteract or reinforce the positive effects of CH2O on the tropospheric ozone increases. The model underestimates the observed tropospheric ozone increase, especially over the US and Europe, because of underestimated NO2 emissions changes used in the model. The stratospheric ozone contribution increases during this period in the Northern Hemisphere and contributes to the tropospheric ozone increase.

Global tropospheric ozone trends, attributions, and radiative impacts in 1995–2017: an integrated analysis using aircraft (IAGOS) observations, ozonesonde, and multi-decadal chemical model simulations

Abstract. Quantification and attribution of long-term tropospheric ozone trends are critical for understanding the impact of human activity and climate change on atmospheric chemistry but are also challenged by the limited coverage of long-term ozone observations in the free troposphere where ozone has higher production efficiency and radiative potential compared to that at the surface. In this study, we examine observed tropospheric ozone trends, their attributions, and radiative impacts from 1995–2017 using aircraft observations from the In-service Aircraft for a Global Observing System database (IAGOS), ozonesondes, and a multi-decadal GEOS-Chem chemical model simulation. IAGOS observations above 11 regions in the Northern Hemisphere and 19 of 27 global ozonesonde sites have measured increases in tropospheric ozone (950–250 hPa) by 2.7 ± 1.7 and 1.9 ± 1.7 ppbv per decade on average, respectively, with particularly large increases in the lower troposphere (950–800 hPa) above East Asia, the Persian Gulf, India, northern South America, the Gulf of Guinea, and Malaysia/Indonesia by 2.8 to 10.6 ppbv per decade. The GEOS-Chem simulation driven by reanalysis meteorological fields and the most up-to-date year-specific anthropogenic emission inventory reproduces the overall pattern of observed tropospheric ozone trends, including the large ozone increases over the tropics of 2.1–2.9 ppbv per decade and above East Asia of 0.5–1.8 ppbv per decade and the weak tropospheric ozone trends above North America, Europe, and high latitudes in both hemispheres, but trends are underestimated compared to observations. GEOS-Chem estimates an increasing trend of 0.4 Tg yr−1 of the tropospheric ozone burden in 1995–2017. We suggest that uncertainties in the anthropogenic emission inventory in the early years of the simulation (e.g., 1995–1999) over developing regions may contribute to GEOS-Chem's underestimation of tropospheric ozone trends. GEOS-Chem sensitivity simulations show that changes in global anthropogenic emission patterns, including the equatorward redistribution of surface emissions and the rapid increases in aircraft emissions, are the dominant factors contributing to tropospheric ozone trends by 0.5 Tg yr−1. In particular, we highlight the disproportionately large, but previously underappreciated, contribution of aircraft emissions to tropospheric ozone trends by 0.3 Tg yr−1, mainly due to aircraft emitting NOx in the mid-troposphere and upper troposphere where ozone production efficiency is high. Decreases in lower-stratospheric ozone and the stratosphere–troposphere flux in 1995–2017 contribute to an ozone decrease at mid-latitudes and high latitudes. We estimate the change in tropospheric ozone radiative impacts from 1995–1999 to 2013–2017 is +18.5 mW m−2, with 43.5 mW m−2 contributed by anthropogenic emission changes (20.5 mW m−2 alone by aircraft emissions), highlighting that the equatorward redistribution of emissions to areas with strong convection and the increase in aircraft emissions are effective for increasing tropospheric ozone's greenhouse effect.

Changes in tropospheric ozone concentration over Indo-Gangetic Plains: the role of meteorological parameters

This study seeks to understand and quantify the changes in tropospheric ozone (O3) in lower troposphere (LT), middle troposphere (MT) and upper middle troposphere (UMT) over the Indo-Gangetic Plains (IGPs), India during the COVID-19 lockdown 2020 with that of pre-lockdown 2019. The gridded datasets of ozone from the European Centre for Medium-range Weather Forecasts (ECMWF) reanalysis product, ERA5 in combination with statistical interpolated (IDWs) surface NO2 observations, present a consistent picture and indicate a significant tropospheric ozone enhancement over IGP during COVID-19 lockdown restrictions in May 2020. The Paper also examines the influencing role of meteorological parameters on increasing ozone concentration. Over LT, an increase in O3 concentration (23%) is observed and in MT to UMT an enhancement of about 9–18% in O3 concentration have been seen during May 2020 with respect to May 2019. An investigation on causes of increasing ozone concentration (35–85 ppbv) from MT to UMT during May 2020 reveals that there was significant rise (by 1–6%) in low cloud cover (LCC). Notably, higher LCC increases the backscattering of upward solar radiation from the top of the atmosphere. A positive difference of 5–25 W/m2 in upward solar radiation (USR) is observed across the entire study region. The result suggests that higher LCC significantly contributed to the enhanced USR. Thereby, resulting in higher photolysis rate that lead to an increase in mid tropospheric ozone concentration during May 2020. The results highlight the importance of LCC as an important pathway in ozone formation and aid in scientific understanding of it.

Attribution of Stratospheric and Tropospheric Ozone Changes Between 1850 and 2014 in CMIP6 Models

AbstractWe quantify the impacts of halogenated ozone‐depleting substances (ODSs), greenhouse gases (GHGs), and short‐lived ozone precursors on ozone changes between 1850 and 2014 using single‐forcing perturbation simulations from several Earth system models with interactive chemistry participating in the Coupled Model Intercomparison Project Aerosol and Chemistry Model Intercomparison Project. We present the responses of ozone to individual forcings and an attribution of changes in ozone columns and vertically resolved stratospheric and tropospheric ozone to these forcings. We find that whilst substantial ODS‐induced ozone loss dominates the stratospheric ozone changes since the 1970s, in agreement with previous studies, increases in tropospheric ozone due to increases in short‐lived ozone precursors and methane since the 1950s make increasingly important contributions to total column ozone (TCO) changes. Increases in methane also lead to substantial extra‐tropical stratospheric ozone increases. Impacts of nitrous oxide and carbon dioxide on stratospheric ozone are significant but their impacts on TCO are small overall due to several opposing factors and are also associated with large dynamical variability. The multi‐model mean (MMM) results show a clear change in the stratospheric ozone trends after 2000 due to now declining ODSs, but the trends are generally not significantly positive, except in the extra‐tropical upper stratosphere, due to relatively small changes in forcing over this period combined with large model uncertainty. Although the MMM ozone compares well with the observations, the inter‐model differences are large primarily due to the large differences in the models' representation of ODS‐induced ozone depletion.

Impact of eastern and central Pacific El Niño on lower tropospheric ozone in China

Abstract. Tropospheric ozone, as a critical atmospheric component, plays an important role in influencing radiation equilibrium and ecological health. It is affected not only by anthropogenic activities but also by natural climate variabilities. Here we examine the tropospheric ozone changes in China associated with the eastern Pacific (EP) and central Pacific (CP) El Niño using satellite observations from 2007 to 2017 and GEOS-Chem simulations from 1980 to 2017. GEOS-Chem reasonably reproduced the satellite-retrieved lower tropospheric ozone (LTO) changes despite a slight underestimation. In general, both types of El Niño exert negative impacts on LTO concentration in China, except for southeastern China during the pre-CP El Niño autumn and post-EP El Niño summer. Ozone budget analysis further reveals that for both events, LTO changes are dominated by the transport processes controlled by circulation patterns and the chemical processes influenced by local meteorological anomalies associated with El Niño, especially the changes in solar radiation and relative humidity. The differences between EP- and CP-induced LTO changes mostly lie in southern China. The different strengths, positions, and duration of the western North Pacific anomalous anticyclone induced by tropical warming are likely responsible for the different EP and CP LTO changes. During the post-EP El Niño summer, the Indian Ocean capacitor effect also plays an important role in mediating LTO changes over southern China.

Stratospheric ozone depletion and tropospheric ozone increases drive Southern Ocean interior warming

Atmospheric ozone has undergone distinct changes in the stratosphere and troposphere during the second half of the twentieth century, with depletion in the stratosphere and an increase in the troposphere. Until now, the effect of these changes on ocean heat uptake has been unclear. Here we show that both stratospheric and tropospheric ozone changes have contributed to Southern Ocean interior warming with the latter being more important. The ozone changes between 1955 and 2000 induced about 30% of the net simulated ocean heat content increase in the upper 2,000 m of the Southern Ocean, with around 60% attributed to tropospheric increases and 40% to stratospheric depletion. Moreover, these two warming contributions show distinct physical mechanisms: tropospheric ozone increases cause a subsurface warming in the Southern Ocean primarily via the deepening of isopycnals, while stratospheric ozone causes depletion via spiciness changes along isopycnals. Our results highlight that tropospheric ozone is more than an air pollutant and, as a greenhouse gas, has been pivotal to the Southern Ocean warming.

Tropospheric ozone changes and ozone sensitivity from the present day to the future under shared socio-economic pathways

Abstract. Tropospheric ozone is important to future air quality and climate. We investigate ozone changes and ozone sensitivity to changing emissions in the context of climate change from the present day (2004–2014) to the future (2045–2055) under a range of shared socio-economic pathways (SSPs). We apply the United Kingdom Earth System Model, UKESM1, with an extended chemistry scheme including more reactive volatile organic compounds (VOCs) to quantify ozone burdens as well as ozone sensitivities globally and regionally based on nitrogen oxide (NOx) and VOC mixing ratios. We show that the tropospheric ozone burden increases by 4 % under a development pathway with higher NOx and VOC emissions (SSP3-7.0) but decreases by 7 % under the same pathway if NOx and VOC emissions are reduced (SSP3-7.0-lowNTCF) and by 5 % if atmospheric methane (CH4) mixing ratios are reduced (SSP3-7.0-lowCH4). Global mean surface ozone mixing ratios are reduced by 3–5 ppb under SSP3-7.0-lowNTCF and by 2–3 ppb under SSP3-7.0-lowCH4. However, surface ozone changes vary substantially by season in high-emission regions under future pathways, with decreased ozone mixing ratios in summer and increased ozone mixing ratios in winter when NOx emissions are reduced. VOC-limited areas are more extensive in winter (7 %) than in summer (3 %) across the globe. North America, Europe, and East Asia are the dominant VOC-limited regions in the present day, but North America and Europe become more NOx-limited in the future mainly due to reductions in NOx emissions. The impacts of VOC emissions on ozone sensitivity are limited in North America and Europe because reduced anthropogenic VOC emissions are partly offset by higher biogenic VOC emissions. Ozone sensitivity is not greatly influenced by changing CH4 mixing ratios. South Asia becomes the dominant VOC-limited region under future pathways. We highlight that reductions in NOx emissions are required to transform ozone production from VOC to NOx limitation, but that these lead to increased ozone mixing ratios in high-emission regions, and hence emission controls on VOC and CH4 are also necessary.

Land cover change in low-warming scenarios may enhance the climate role of secondary organic aerosols

Most socioeconomic pathways compatible with the aims of the Paris Agreement include large changes to land use and land cover. The associated vegetation changes can interact with the atmosphere and climate through numerous mechanisms. One of these is emissions of biogenic volatile organic compounds (BVOCs), which may lead to the formation of secondary organic aerosols (SOAs) and atmospheric chemistry changes. Here, we use a modeling framework to explore potential future global and regional changes in SOA and tropospheric ozone following idealized, large-scale vegetation perturbations, and their resulting radiative forcing (RF). Guided by projections in low-warming scenarios, we modify crop and forest cover, separately, and in concurrence with changes in anthropogenic emissions and CO2 level. We estimate that increasing global forest cover by 30% gives a 37% higher global SOA burden, with a resulting forcing of −0.13 W m−2. The effect on tropospheric ozone is relatively small. Large SOA burden changes of up to 48% are simulated for South America and Sub-Saharan Africa. Conversely, increasing crop cover at the expense of tropical forest, yields similar changes but of opposite sign. The magnitude of these changes is strongly affected by the concurrent evolution of anthropogenic emissions. Our land cover perturbations are representative of energy crop expansion and afforestation, two key mitigation measures in 1.5 °C compatible scenarios. Our results hence indicate that depending on the role of these two in the underlying mitigation strategies, scenarios with similar long-term global temperature levels could lead to opposite effects on SOA. Combined with the complexity of factors that control SOA, this highlights the importance of including BVOC effects in further studies and assessments of climate and air quality mitigation involving the land surface.

The Increasing Surface Ozone and Tropospheric Ozone in Antarctica and Their Possible Drivers.

A comprehensive analysis of the temporal evolution of tropospheric ozone in Antarctica using more than 25 years of surface ozone and ozonesonde measurements reveals significant changes in tropospheric ozone there. It shows a positive trend in ozone at the surface and lower and mid-troposphere, but a negative trend in the upper troposphere. We also find significant links between different climate modes and tropospheric ozone in Antarctica and observe that changes in residual overturning circulation, the strength of the polar vortex, and stratosphere-troposphere exchange make noticeable variability in tropospheric ozone. Therefore, this study alerts of increasing ozone concentration in Antarctica, which would have a profound impact on the future climate of the region as tropospheric ozone has warming feedback to the Earth's climate.

Influence of aromatics on tropospheric gas-phase composition

Abstract. Aromatics contribute a significant fraction to organic compounds in the troposphere and are mainly emitted by anthropogenic activities and biomass burning. Their oxidation in lab experiments is known to lead to the formation of ozone and aerosol precursors. However, their overall impact on tropospheric composition is uncertain as it depends on transport, multiphase chemistry, and removal processes of the oxidation intermediates. Representation of aromatics in global atmospheric models has been either neglected or highly simplified. Here, we present an assessment of their impact on gas-phase chemistry, using the general circulation model EMAC (ECHAM5/MESSy Atmospheric Chemistry). We employ a comprehensive kinetic model to represent the oxidation of the following monocyclic aromatics: benzene, toluene, xylenes, phenol, styrene, ethylbenzene, trimethylbenzenes, benzaldehyde, and lumped higher aromatics that contain more than nine C atoms. Significant regional changes are identified for several species. For instance, glyoxal increases by 130 % in Europe and 260 % in East Asia, respectively. Large increases in HCHO are also predicted in these regions. In general, the influence of aromatics is particularly evident in areas with high concentrations of NOx, with increases up to 12 % in O3 and 17 % in OH. On a global scale, the estimated net changes of trace gas levels are minor when aromatic compounds are included in our model. For instance, the tropospheric burden of CO increases by about 6 %, while the burdens of OH, O3, and NOx (NO+NO2) decrease between 3 % and 9 %. The global mean changes are small, partially because of compensating effects between high- and low-NOx regions. The largest change is predicted for the important aerosol precursor glyoxal, which increases globally by 36 %. In contrast to other studies, the net change in tropospheric ozone is predicted to be negative, −3 % globally. This change is larger in the Northern Hemisphere where global models usually show positive biases. We find that the reaction with phenoxy radicals is a significant loss for ozone, on the order of 200–300 Tg yr−1, which is similar to the estimated ozone loss due to bromine chemistry. Although the net global impact of aromatics is limited, our results indicate that aromatics can strongly influence tropospheric chemistry on a regional scale, most significantly in East Asia. An analysis of the main model uncertainties related to oxidation and emissions suggests that the impact of aromatics may even be significantly larger.

Changes in Tropospheric Ozone Associated With Strong Earthquakes and Possible Mechanism

The index of ozone anomaly (IOA) has been proposed to detect changes in tropospheric ozone associated with strong earthquakes. The tropospheric ozone prior and after the 2008 Wenchuan earthquake has been analyzed using IOA. Atmospheric infrared sounder ozone volume mixing ratio (O3 VMR) at different pressure levels (600, 500, 400, 300, 200 hPa) for an 18-year period 2003–2020 has been considered to identify the unique behavior associated with the strong earthquakes. Our results show distinct enhancement in tropospheric ozone occurred 5 d (7 May 2008) prior to the main event and distributed along the Longmenshan fault zone. An enhancement in IOA has also been observed around the time of the 2013 Lushan and 2017 Jiuzhaigou earthquakes, but with the different emergence time, which indicates that the unusual behavior of tropospheric ozone depends on the tectonic and geological environment, focal mechanism, focal depth, meteorological conditions, and other factors. The location of increased tropospheric ozone indicates the epicenter of earthquakes. The magnitude of earthquake could be one of the important factors affecting the appearance of the anomalous tropospheric ozone. The possible mechanism for the increased tropospheric ozone associated with strong earthquakes is discussed in this article. The quasi-synchronous changes of tropospheric ozone and other parameters in the lithosphere/atmosphere/ionosphere have been found by combining with the other published results related to the Wenchuan earthquake, which show the existence of coupling during the earthquake preparation phase associated with the lithosphere–atmosphere–ionosphere coupling.

Impact of weather and emission changes on NO2 concentrations in China during 2014-2019.

Nitrogen dioxide (NO2) is one of the most important air pollutants that highly affect the formation of secondary fine particles and tropospheric ozone. In this study based on hourly NO2 observations from June 2014 to May 2019 and a regional air quality model (WRF-CMAQ), we comprehensively analyzed the spatiotemporal variations of NO2 concentrations throughout China and in 12 urban agglomerations (UAs) and quantitatively showed the anthropogenic and meteorological factors controlling the interannual variations (IAVs). The ground observations and tropospheric columns show that high NO2 concentrations are predominantly concentrated in UAs such as Beijing-Tianjin-Hebei (BTH), the Shandong Peninsula (SP), the Central Plain (CP), Central Shaanxi (CS), and the Yangtze River Delta (YRD). For different UAs, the NO2 IAVs are different. The NO2 increased first and then decreased in 2016 or 2017 in BTH, YRD, CS, and Cheng-Yu, and decreased from 2014 to 2019 in Harbin-Changchun, CP, SP, Northern Slope of Tianshan Mountain, and Beibu-Gulf, while increased slightly in the Pearl River Delta (PRD) and Hohhot-Baotou-Erdos-Yulin (HBEY). The NO2 IAVs were primarily dominated by emission changes. The net wintertime decreases of NO2 in BTH, Yangtze River Middle-Reach, and PRD were mostly contributed by emission reductions from 2014 to 2018, and the significant increase in the wintertime in HBEY was also dominated by emission changes (93%). Weather conditions also have an important effect on the NO2 IAVS. In BTH and HBEY, the increases of NO2 in winter of 2016 are mainly attributed to the unfavorable weather conditions and for the significant decreases in the winter of 2017, the favorable weather conditions also play a very important role. This study provides a basic understanding on the current situation of NO2 pollution and are helpful for policymakers as well as those interested in the study of tropospheric ozone changes in China and downwind areas.

Stratospheric Ozone in the Last Glacial Maximum

AbstractUsing the Whole Atmosphere Community Climate Model version 6, stratospheric ozone in the Last Glacial Maximum (LGM) is investigated. It is shown that, compared with preindustrial (PI) times, LGM modeled stratospheric temperatures are increased by up to 8 K, leading to faster ozone destruction rates for gas phase reactions, especially via the Chapman mechanism. On the other hand, stratospheric hydroxyl radical (OH) and nitrogen oxides (NOx) concentrations are decreased by 10–20%, which decreases catalytic ozone destruction, thereby decreasing ozone loss rates. The net effect of these two compensating mechanisms in the upper stratosphere (above 15 hPa) is a vertically integrated 1–3 Dobson unit (DU) decrease during the LGM. In the lower stratosphere (tropopause to 15 hPa), changes in the stratospheric overturning circulation and resulting transport dominate changes in ozone. Consistent with a weakening of the residual circulation in the LGM, lower stratospheric ozone is increased by 2–5 DU in the tropics and decreased by 5–10 DU in the extratropics, but the latter is partly compensated by ozone increases due to a lower tropopause. It is found that tropospheric ozone is decreased by about 5 DU in the LGM versus PI. Combined changes in stratospheric and tropospheric ozone lead to a decrease in total ozone column everywhere except over the northeast North America, equatorial Indian and West Pacific Oceans. Surface ultraviolet radiation in the LGM versus PI is increased over the Northern Hemisphere middle and high latitudes, especially over the ice caps, and over the Southern Hemisphere near 60°S.

Examining the relationship of tropospheric ozone and climate change on crop productivity using the multivariate panel data techniques

Home to one-fourth of the world's population and ranked amongst the fastest growing economies, the South Asian countries are marred with the predicament of inexorable pollution. Amidst the growing pollutants, ground-level ozone has become an important component in understanding health, and productivity of agricultural crops. In this regard spatio-temporal analysis of tropospheric ozone for wheat, rice and cotton crops was carried out. Followed-up with a multivariate regression model; establishing a statistical relationship between tropospheric ozone (TO) and crop productivity. The results indicate that predominantly ozone is increasing, with a significant trend visible in all crop growing seasons. Observations indicate higher concentrations of TO in the rice & cotton growing seasons, with a seasonal average of 68 ppb, compared to wheat growing season (55 ppb). Regression results specify that with an increase of 1% in tropospheric ozone concentration within the study area; crop productivity decreases for cotton (−4.0%), rice (−2.3%), and wheat (−0.7%). Furthermore, with the presence of the dominant tropospheric ozone in the regression model, the temperature's impact on productivity becomes statistically inconsequential.

Climate, pollution and California’s crops

Historical and projected impacts of tropospheric ozone and climate change on California’s most valuable perennial crops indicate that opportunities exist to improve crop yields through pollution mitigation.

Compensatory climate effects link trends in global runoff to rising atmospheric CO2 concentration

River runoff is a key attribute of the land surface, that additionally has a strong influence on society by the provision of freshwater. Yet various environmental factors modify runoff levels, and some trends could be detrimental to humanity. Drivers include elevated CO2 concentration, climate change, aerosols and altered land-use. Additionally, nitrogen deposition and tropospheric ozone changes influence plant functioning, and thus runoff, yet their importance is less understood. All these effects are now included in the JULES-CN model. We first evaluate runoff estimates from this model against 42 large basin scales, and then conduct factorial simulations to investigate these mechanisms individually. We determine how different drivers govern the trends of runoff over three decades for which data is available. Numerical results suggest rising atmospheric CO2 concentration is the most important contributor to the global mean runoff trend, having a significant mean increase of +0.18 ± 0.006 mm yr−2 and due to the overwhelming importance of physiological effects. However, at the local scale, the dominant influence on historical runoff trends is climate in 82% of the global land area. This difference is because climate change impacts, mainly due to precipitation changes, can be positive (38% of global land area) or negative (44% of area), depending on location. For other drivers, land use change leads to increased runoff trends in wet tropical regions and decreased runoff in Southeast China, Central Asia and the eastern USA. Modelling the terrestrial nitrogen cycle in general suppresses runoff decreases induced by the CO2 fertilization effect, highlighting the importance of carbon–nitrogen interactions on ecosystem hydrology. Nitrogen effects do, though, induce decreasing trend components for much of arid Australia and the boreal regions. Ozone influence was mainly smaller than other drivers.

The impact of ozone exposure, temperature and CO2 on the growth and yield of three spring wheat varieties

When assessing potentials for crop production under future climatic conditions, multiple environmental parameters need to be included. An increase in carbon dioxide [CO2], higher temperatures, and regional changes in tropospheric ozone [O3] will influence the growth responses of existing crop species and varieties. Ozone is phytotoxic and a plant stressor at current concentrations, reducing yields worldwide, but possible interactions with changes in other abiotic factors have been considered very little. In this study, we have used eight combinations: two levels of temperature, two levels of [CO2], and three [O3] exposure regimes to assess the impact of medium-to-high ozone concentrations (80–100 ppb) on wheat growth when other abiotic factors change. Two modern spring wheat varieties (KWS Bittern and Lennox) and a landrace variety (Lantvete) were grown to maturity in climate chambers. We examined plant performance during growth as development rate, rate of photosynthesis, stomatal conductance, water use, and at harvest as total aboveground dry matter and grain yield. All three varieties lost yield in all treatments compared to the ambient treatment that had the following settings: Lowest temperature, ambient [CO2], and very low [O3]. For episodic ozone exposure in the ambient or high [CO2] and high-level temperature treatment, the yield losses were 18 and 25%, respectively, for KWS Bittern; 44 and 34% for Lennox; and 16 and 37% for Lantvete. The yields of the modern varieties are significantly higher than the landrace variety in two out of eight treatments, although they are higher by weight in seven of the eight treatments. The landrace variety’s fraction loss from its highest grain yield in the ambient treatment to the high-[CO2]-and high-level-temperature-treatments was smaller than the modern varieties’, showing a comparably higher degree of plasticity of performance. Current crop varieties might be more sensitive to ozone than older varieties, emphasizing the need of future breeding programs to expand the gene pool to provide more climate robust crops.

Interannual and Decadal Changes in Tropospheric Ozone in China and the Associated Chemistry-Climate Interactions: A Review

China has been experiencing widespread air pollution due to rapid industrialization and urbanization in recent decades. The two major concerns of ambient air quality in China are particulate matter (PM) and tropospheric ozone (O3). With the implementation of air pollution prevention and control actions in the last five years, the PM pollution in China has been substantially reduced. In contrast, under the conditions of the urban air pollution complex, the elevated O3 levels in city clusters of eastern China, especially in warm seasons, have drawn increasing attention. Emissions of air pollutants and their precursors not only contribute to regional air quality, but also alter climate. Climate change in turn can change chemical processes, long-range transport, and local meteorology that influence air pollution. Compared to PM, less is known about O3 pollution and its climate effects over China. Here, we present a review of the main findings from the literature over the period 2011–18 with regard to the characteristics of O3 concentrations in China and the mechanisms that drive its interannual to decadal variations, aiming to identify robust conclusions that may guide decision-making for emissions control and to highlight critical knowledge gaps. We also review regional and global modeling studies that have investigated the impacts of tropospheric O3 on climate, as well as the projections of future tropospheric O3 owing to climate and/or emission changes.