Analysis of European ozone trends in the period 1995–2014

Abstract. Surface-based measurements from the EMEP and Airbase networks are used to estimate the changes in surface ozone levels during the 1995–2014 period over Europe. We find significant ozone enhancements (0.20–0.59 µg m−3 yr−1 for the annual means; P-value  <  0.01 according to an F-test) over the European suburban and urban stations during 1995–2012 based on the Airbase sites. For European background ozone observed at EMEP sites, it is shown that a significantly decreasing trend in the 95th percentile ozone concentrations has occurred, especially at noon (0.9 µg m−3 yr−1; P-value  <  0.01), while the 5th percentile ozone concentrations continued to increase with a trend of 0.3 µg m−3 yr−1 (P-value  <  0.01) during the study period. With the help of numerical simulations performed with the global chemistry-climate model EMAC, the importance of anthropogenic emissions changes in determining these changes over background sites are investigated. The EMAC model is found to successfully capture the observed temporal variability in mean ozone concentrations, as well as the contrast in the trends of 95th and 5th percentile ozone over Europe. Sensitivity simulations and statistical analysis show that a decrease in European anthropogenic emissions had contrasting effects on surface ozone trends between the 95th and 5th percentile levels and that background ozone levels have been influenced by hemispheric transport, while climate variability generally regulated the inter-annual variations of surface ozone in Europe.

Download Full-text

Analysis of European ozone trends in the period 1995–2014

10.5194/acp-2017-1077 ◽

2017 ◽

Cited By ~ 1

Author(s):

Yingying Yan ◽

Andrea Pozzer ◽

Narendra Ojha ◽

Jintai Lin ◽

Jos Lelieveld

Keyword(s):

Statistical Analysis ◽

Temporal Variability ◽

Climate Model ◽

Surface Ozone ◽

Anthropogenic Emissions ◽

Annual Variations ◽

Ozone Concentrations ◽

Background Ozone ◽

Ozone Trends ◽

Ozone Levels

Abstract. Surface-based measurements from the EMEP network are used to estimate the changes in surface ozone levels during the 1995–2014 period over Europe. It is shown that a significantly decreasing trend in the 95th percentile ozone concentrations has occurred, especially during noontime (0.9 µg/m3/y), while the 5th percentile ozone concentrations continued to increase with a trend of 0.3 µg/m3/y during the study period. With the help of numerical simulations performed with the global chemistry-climate model EMAC, the importance of anthropogenic emissions changes in determining these changes are investigated. The EMAC model is found to successfully capture the observed temporal variability in mean ozone concentrations, as well as the contrast in the trends of 95th and 5th percentile ozone over Europe. Sensitivity simulations and statistical analysis show that a decrease in European anthropogenic emissions had contrasting effects on surface ozone trends between the 95th and 5th percentile levels, and that background ozone levels have been influenced by hemispheric transport, while climate variability generally regulated the inter-annual variations of surface ozone in Europe.

Download Full-text

US surface ozone trends and extremes from 1980–2014: Quantifying the roles of rising Asian emissions, domestic controls, wildfires, and climate

10.5194/acp-2016-1093 ◽

2016 ◽

Cited By ~ 1

Author(s):

Meiyun Lin ◽

Larry W. Horowitz ◽

Richard Payton ◽

Arlene M. Fiore ◽

Gail Tonnesen

Keyword(s):

Climate Model ◽

Heat Waves ◽

Surface Ozone ◽

Anthropogenic Emissions ◽

Daily Maximum ◽

Western Us ◽

Emission Controls ◽

Ozone Trends ◽

The Usa ◽

Rural Sites

Abstract. Surface ozone (O3) responds to varying global-to-regional precursor emissions, climate, and extreme weather, with implications for designing effective air quality control policies. We examine these conjoined processes with observations and global chemistry-climate model (GFDL-AM3) hindcasts over 1980–2014. The model captures the salient features of observed trends in daily maximum 8-hour average O3; (1) increases over East Asia (up to 2 ppb yr−1), (2) springtime increases at western US (WUS) rural sites (0.2–0.5 ppb yr−1) with a ‘baseline’ sampling approach, (3) summertime decreases, largest at the 95th percentile, and wintertime increases in the 50th to 5th percentiles over the eastern US (EUS). Asian NOx emissions tripled since 1990, contributing as much as 65 % to modeled springtime background O3 increases (0.3–0.5 ppb yr−1) over the WUS, outpacing O3 decreases attained via US domestic emission controls. Methane increases over this period raise WUS background O3 by 15 %. During summer, increasing Asian emissions approximately offset the effects of US emission reductions, leading to weak or insignificant observed O3 trends at WUS rural sites. While wildfire emissions can enhance summertime monthly mean O3 at individual sites by 2–8 ppb, high temperatures and the associated buildup of O3 produced from regional anthropogenic emissions contribute most to elevating observed summertime O3 throughout the USA. Rising Asian emissions and global methane under the RCP8.5 scenario increase mean springtime O3 above the WUS by ~ 10 ppb from 2010 to 2030. Historical EUS O3 decreases, driven by regional emission controls, were most pronounced in the Southeast with an earlier onset of biogenic isoprene emissions and NOx-sensitive O3 production. Regional NOx reductions also alleviated the O3 buildup during the recent heat waves of 2011 and 2012 relative to earlier heat waves (e.g., 1988; 1999). Without emission controls, the 95th percentile summertime O3 in the EUS would have increased by 0.2–0.4 ppb yr−1 over 1988–2014 due to more frequent hot extremes and rising biogenic isoprene emissions.

Download Full-text

Impact of climate change on tropospheric ozone and its global budgets

Atmospheric Chemistry and Physics ◽

10.5194/acp-8-369-2008 ◽

2008 ◽

Vol 8 (2) ◽

pp. 369-387 ◽

Cited By ~ 114

Author(s):

G. Zeng ◽

J. A. Pyle ◽

P. J. Young

Keyword(s):

Climate Change ◽

Tropospheric Ozone ◽

Climate Model ◽

Surface Ozone ◽

Lower Troposphere ◽

Ozone Production ◽

Anthropogenic Emissions ◽

Free Troposphere ◽

Tropical Ocean ◽

Ozone Levels

Abstract. We present the chemistry-climate model UMCAM in which a relatively detailed tropospheric chemical module has been incorporated into the UK Met Office's Unified Model version 4.5. We obtain good agreements between the modelled ozone/nitrogen species and a range of observations including surface ozone measurements, ozone sonde data, and some aircraft campaigns. Four 2100 calculations assess model responses to projected changes of anthropogenic emissions (SRES A2), climate change (due to doubling CO2), and idealised climate change-associated changes in biogenic emissions (i.e. 50% increase of isoprene emission and doubling emissions of soil-NOx). The global tropospheric ozone burden increases significantly for all the 2100 A2 simulations, with the largest response caused by the increase of anthropogenic emissions. Climate change has diverse impacts on O3 and its budgets through changes in circulation and meteorological variables. Increased water vapour causes a substantial ozone reduction especially in the tropical lower troposphere (>10 ppbv reduction over the tropical ocean). On the other hand, an enhanced stratosphere-troposphere exchange of ozone, which increases by 80% due to doubling CO2, contributes to ozone increases in the extratropical free troposphere which subsequently propagate to the surface. Projected higher temperatures favour ozone chemical production and PAN decomposition which lead to high surface ozone levels in certain regions. Enhanced convection transports ozone precursors more rapidly out of the boundary layer resulting in an increase of ozone production in the free troposphere. Lightning-produced NOx increases by about 22% in the doubled CO2 climate and contributes to ozone production. The response to the increase of isoprene emissions shows that the change of ozone is largely determined by background NOx levels: high NOx environment increases ozone production; isoprene emitting regions with low NOx levels see local ozone decreases, and increase of ozone levels in the remote region due to the influence of PAN chemistry. The calculated ozone changes in response to a 50% increase of isoprene emissions are in the range of between −8 ppbv to 6 ppbv. Doubling soil-NOx emissions will increase tropospheric ozone considerably, with up to 5 ppbv in source regions.

Download Full-text

Impact of climate change on tropospheric ozone and its global budgets

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-7-11141-2007 ◽

2007 ◽

Vol 7 (4) ◽

pp. 11141-11189 ◽

Cited By ~ 6

Author(s):

G. Zeng ◽

J. A. Pyle ◽

P. J. Young

Keyword(s):

Climate Change ◽

Tropospheric Ozone ◽

Climate Model ◽

Surface Ozone ◽

Lower Troposphere ◽

Ozone Production ◽

Anthropogenic Emissions ◽

Free Troposphere ◽

Tropical Ocean ◽

Ozone Levels

Abstract. We present the chemistry-climate model UM_CAM in which a relatively detailed tropospheric chemical module has been incorporated into the UK Met Office's Unified Model version 4.5. We obtain good agreements between the modelled ozone/nitrogen species and a range of observations including surface ozone measurements, ozone sonde data, and some aircraft campaigns. Four 2100 calculations assess model responses to projected changes of anthropogenic emissions (SRES A2), climate change (due to doubling CO2), and idealised climate change associated changes in biogenic emissions (i.e. 50% increase of isoprene emission and doubling emissions of soil-NOx). The global tropospheric ozone burden increases significantly for all the 2100 A2 simulations, with the largest response caused by the increase of anthropogenic emissions. Climate change has diverse impacts on O3 and its budgets through changes in circulation and meteorological variables. Increased water vapour causes a substantial ozone reduction especially in the tropical lower troposphere (>10 ppbv reduction over the tropical ocean). On the other hand, an enhanced stratosphere-troposphere exchange of ozone, which increases by 80% due to doubling CO2, contributes to ozone increases in the extratropical free troposphere which subsequently propagate to the surface. Projected higher temperatures favour ozone chemical production and PAN decomposition which lead to high surface ozone levels in certain regions. Enhanced convection transports ozone precursors more rapidly out of the boundary layer resulting in an increase of ozone production in the free troposphere. Lightning-produced NOx increases by about 22% in the doubled CO2 climate and contributes to ozone production. The response to the increase of isoprene emissions shows that the change of ozone is largely determined by background NOx levels: high NOx environment increases ozone production; isoprene emitting regions with low NOx levels see local ozone decreases, and increase of ozone levels in the remote region due to the influence of PAN chemistry. The calculated ozone changes in response to a 50% increase of isoprene emissions are in the range of between –8 ppbv to 6 ppbv. Doubling soil-NOx emissions will increase tropospheric ozone considerably, with up to 5 ppbv in source regions.

Download Full-text

Temporal patterns and trends of surface ozone concentrations over Portugal

10.5194/egusphere-egu21-5119 ◽

2021 ◽

Author(s):

Carla Gama ◽

Alexandra Monteiro ◽

Myriam Lopes ◽

Ana Isabel Miranda

Keyword(s):

Air Quality ◽

Iberian Peninsula ◽

Human Health ◽

Temporal Variability ◽

Urban Areas ◽

Surface Ozone ◽

Quality Data ◽

Ozone Concentrations ◽

Long Term Study

Tropospheric ozone (O3) is a critical pollutant over the Mediterranean countries, including Portugal, due to systematic exceedances to the thresholds for the protection of human health. Due to the location of Portugal, on the Atlantic coast at the south-west point of Europe, the observed O3 concentrations are very much influenced not only by local and regional production but also by northern mid-latitudes background concentrations. Ozone trends in the Iberian Peninsula were previously analysed by Monteiro et al. (2012), based on 10-years of O3 observations. Nevertheless, only two of the eleven background monitoring stations analysed in that study are located in Portugal and these two stations are located in Porto and Lisbon urban areas. Although during pollution events O3 levels in urban areas may be high enough to affect human health, the highest concentrations are found in rural locations downwind from the urban and industrialized areas, rather than in cities. This happens because close to the sources (e.g., in urban areas) freshly emitted NO locally scavenges O3. A long-term study of the spatial and temporal variability and trends of the ozone concentrations over Portugal is missing, aiming to answer the following questions:-&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; What is the temporal variability of ozone concentrations?-&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; Which trends can we find in observations?-&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; How were the ozone spring maxima concentrations affected by the COVID-19 lockdown during spring 2020?In this presentation, these questions will be answered based on the statistical analysis of O3 concentrations recorded within the national air quality monitoring network between 2005 and 2020 (16 years). The variability of the surface ozone concentrations over Portugal, on the timescales from diurnal to annual, will be presented and discussed, taking into account the physical and chemical processes that control that variability. Using the TheilSen function from the OpenAir package for R (Carslaw and Ropkins 2012), which quantifies monotonic trends and calculates the associated p-value through bootstrap simulations, O3 concentration long-term trends will be estimated for the different regions and environments (e.g., rural, urban).&#160; Moreover, taking advantage of the unique situation provided by the COVID-19 lockdown during spring 2020, when the government imposed mandatory confinement and citizens movement restriction, leading to a reduction in traffic-related atmospheric emissions, the role of these emissions on ozone levels during the spring period will be studied and presented.&#160;Carslaw and Ropkins, 2012. Openair&#8212;an R package for air quality data analysis. Environ. Model. Softw. 27-28,52-61. https://doi.org/10.1016/j.envsoft.2011.09.008Monteiro et al., 2012. Trends in ozone concentrations in the Iberian Peninsula by quantile regression and clustering. Atmos. Environ. 56, 184-193. https://doi.org/10.1016/j.atmosenv.2012.03.069

Download Full-text

Sensitivities of isoprene emissions to soil moisture and impacts on surface ozone levels as simulated over the Euro-Mediterranean region by the regional climate model RegCM4.7chem-CLM4.5-MEGAN2.1

10.5194/egusphere-egu21-3005 ◽

2021 ◽

Author(s):

Susanna Strada ◽

Andrea Pozzer ◽

Graziano Giuliani ◽

Erika Coppola ◽

Fabien Solmon ◽

...

Keyword(s):

Soil Moisture ◽

Water Stress ◽

Regional Climate Model ◽

Mediterranean Region ◽

Control Experiment ◽

Climate Model ◽

Surface Ozone ◽

Regional Climate ◽

Activity Factor ◽

Ozone Levels

In response to changes in environmental conditions (e.g., temperature, radiation, soil moisture), plants emit biogenic volatile organic compounds (BVOCs). In the large family of BVOCs, isoprene dominates and plays an important role in atmospheric chemistry. Once released in the atmosphere, isoprene influences levels of ozone, thus affecting both climate and air quality. In turn, climate change may alter isoprene emissions by increasing the occurrence and intensity of severe thermal and water stresses that alter plant functioning. To better constrain the evolution of isoprene emissions under future climates, it is critical to reduce the uncertainties in global and regional estimates of isoprene under present climate. Part of these uncertainties is related to the impact of water stress on isoprene. Recently, the BVOC emission model MEGAN has adopted a more sophisticated soil moisture activity factor &#947;sm which does not only account, as previously, for soil moisture available to plants but also links isoprene emissions to photosynthesis and plant water stress.To assess the effects of soil moisture on isoprene emissions and, lastly, on ozone levels in the Euro-Mediterranean region, we use the regional climate model RegCM4.7, coupled to the land surface model CLM4.5, MEGAN2.1 and a chemistry module (RegCM4.7chem-CLM4.5-MEGAN2.1). We have performed a control experiment over 1987-2016 (with a 5-yr spin-up) at a horizontal resolution of 0.22&#176;. Model output from the control experiment is used to initialize RegCM4.7chem-CLM4.5-MEGAN2.1 for the 10 most dry/wet summers (May-August) selected referring to the 1970-2016 precipitation climatology. Each May-August experiment is run with the old and with the new MEGAN soil moisture activity factor &#947;sm.&#160; The results are then compared with a simulation whit no soil moisture activity factor. Both activity factors &#947;sm reduce isoprene emissions under water deficit.During dry summers, the old soil moisture activity factor reduces isoprene emissions homogeneously over the model domain by nearly 100%, while ozone levels decrease by around 10%. When the new &#947;sm is used,isoprene emissions are reduced with a patchy pattern by 10-20%, while ground-surface ozone levels diminish homogeneously by few percent over the southern part of the model domain.

Download Full-text

Seasonal and spatial variability of surface ozone over China: contributions from background and domestic pollution

Atmospheric Chemistry and Physics ◽

10.5194/acp-11-3511-2011 ◽

2011 ◽

Vol 11 (7) ◽

pp. 3511-3525 ◽

Cited By ~ 105

Author(s):

Y. Wang ◽

Y. Zhang ◽

J. Hao ◽

M. Luo

Keyword(s):

Yangtze River ◽

Transport Model ◽

Surface Ozone ◽

Eastern China ◽

Long Range Transport ◽

Anthropogenic Emissions ◽

Spatial Gradient ◽

Chemical Transport Model ◽

Background Ozone ◽

Range Transport

Abstract. Both observations and a 3-D chemical transport model suggest that surface ozone over populated eastern China features a summertime trough and that the month when surface ozone peaks differs by latitude and region. Source-receptor analysis is used to quantify the contributions of background ozone and Chinese anthropogenic emissions on this variability. Annual mean background ozone over China shows a spatial gradient from 55 ppbv in the northwest to 20 ppbv in the southeast, corresponding with changes in topography and ozone lifetime. Pollution background ozone (annual mean of 12.6 ppbv) shows a minimum in the summer and maximum in the spring. On the monthly-mean basis, Chinese pollution ozone (CPO) has a peak of 20–25 ppbv in June north of the Yangtze River and in October south of it, which explains the peaks of surface ozone in these months. The summertime trough in surface ozone over eastern China can be explained by the decrease of background ozone from spring to summer (by −15 ppbv regionally averaged over eastern China). Tagged simulations suggest that long-range transport of ozone from northern mid-latitude continents (including Europe and North America) reaches a minimum in the summer, whereas ozone from Southeast Asia exhibits a maximum in the summer over eastern China. This contrast in seasonality provides clear evidence that the seasonal switch in monsoonal wind patterns plays a significant role in determining the seasonality of background ozone over China.

Download Full-text

Seasonal and spatial variability of surface ozone over China: contributions from background and domestic pollution

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-10-27853-2010 ◽

2010 ◽

Vol 10 (11) ◽

pp. 27853-27891 ◽

Cited By ~ 1

Author(s):

Y. Wang ◽

Y. Zhang ◽

J. Hao ◽

M. Luo

Keyword(s):

Yangtze River ◽

Transport Model ◽

Surface Ozone ◽

Eastern China ◽

Chemical Transport ◽

Anthropogenic Emissions ◽

Spatial Gradient ◽

Chemical Transport Model ◽

Significant Drop ◽

Background Ozone

Abstract. Both observations and a 3-D chemical transport model suggest that surface ozone over populated eastern China features a significant drop in mid-summer and that the peak month differs by latitude and region. Source-receptor analysis is used to quantify the contributions of background ozone and Chinese anthropogenic emissions on this variability. Annual mean background ozone over China shows a spatial gradient from 55 ppbv in the northwest to 20 ppbv in the southeast, corresponding with changes in topography and ozone lifetime. Anthropogenic background (annual mean of 12.6 ppbv) shows distinct troughs in the summer and peaks in the spring. On the monthly-mean basis, Chinese pollution ozone (CPO) has a peak of 20–25 ppbv in June north of the Yangtze River and in October south of it, which explains the peaks of surface ozone in these months. The mid-summer drop in ozone over eastern China is driven by the decrease of background ozone (−15 ppbv). Tagged simulations suggest that this decrease is driven by reduced transport from Europe and North America, whereas ozone from Southeast Asia and Pacific Ocean exhibits a maximum in the summer over eastern China. This contrast in seasonality provides clear evidence that the seasonal switch in monsoonal wind patterns plays a significant role in determining the seasonality of background ozone over China.

Download Full-text

Can we explain the trends in European ozone levels?

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-5-5957-2005 ◽

2005 ◽

Vol 5 (4) ◽

pp. 5957-5985 ◽

Cited By ~ 5

Author(s):

J. E. Jonson ◽

D. Simpson ◽

H. Fagerli ◽

S. Solberg

Keyword(s):

North Atlantic ◽

Polar Region ◽

Surface Ozone ◽

Lateral Boundary ◽

Model Calculations ◽

The North ◽

Ozone Trends ◽

Ozone Precursor ◽

Ozone Episodes ◽

Ozone Levels

Abstract. Ozone levels in Europe are changing. Emissions of ozone precursors from Europe (NOx, CO and non-methane hydrocarbons) have been substantially reduced over the last 10–15 years, but changes in ozone levels can not be explained by changes in European emissions alone. In order to explain the European trends in ozone since 1990 the EMEP regional photochemistry model has been run for the the years 1990 and 1995–2002. The EMEP model is a regional model centered over Europe but the model domain also includes most of the North Atlantic and the polar region. Climatological ozone data are used as initial and lateral boundary concentrations. Model results are compared to measurements over this timespan of 12 years. Possible causes for the measured trends in European surface ozone have been investigated using model sensitivity runs perturbing emissions and lateral boundary concentrations. The observed ozone trends at many European sites are only partially reproduced by global or regional photochemistry models, and possible reasons for this are discussed. The increase in winter ozone partially and the decrease in the magnitude of high ozone episodes is attributed to the decrease in ozone precursor emissions since 1990 by the model. Furthermore, the model calculations indicate that the emission reductions has resulted in a marked decrease in summer ozone in major parts of Europe, and in particular in Germany. Such a trend in summer ozone is likely to be difficult to identify from the measurements because of large inter-annual variability.

Download Full-text

Solar “brightening” impact on summer surface ozone between 1990 and 2010 in Europe – a model sensitivity study of the influence of the aerosol–radiation interactions

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-9741-2018 ◽

2018 ◽

Vol 18 (13) ◽

pp. 9741-9765 ◽

Cited By ~ 3

Author(s):

Emmanouil Oikonomakis ◽

Sebnem Aksoyoglu ◽

Martin Wild ◽

Giancarlo Ciarelli ◽

Urs Baltensperger ◽

...

Keyword(s):

Air Quality ◽

Surface Ozone ◽

Biogenic Emissions ◽

Base Case ◽

Air Quality Model ◽

Quality Model ◽

Ozone Concentrations ◽

Photolysis Rates ◽

Ozone Trends ◽

The Impact

Abstract. Surface solar radiation (SSR) observations have indicated an increasing trend in Europe since the mid-1980s, referred to as solar “brightening”. In this study, we used the regional air quality model, CAMx (Comprehensive Air Quality Model with Extensions) to simulate and quantify, with various sensitivity runs (where the year 2010 served as the base case), the effects of increased radiation between 1990 and 2010 on photolysis rates (with the PHOT1, PHOT2 and PHOT3 scenarios, which represented the radiation in 1990) and biogenic volatile organic compound (BVOC) emissions (with the BIO scenario, which represented the biogenic emissions in 1990), and their consequent impacts on summer surface ozone concentrations over Europe between 1990 and 2010. The PHOT1 and PHOT2 scenarios examined the effect of doubling and tripling the anthropogenic PM2.5 concentrations, respectively, while the PHOT3 investigated the impact of an increase in just the sulfate concentrations by a factor of 3.4 (as in 1990), applied only to the calculation of photolysis rates. In the BIO scenario, we reduced the 2010 SSR by 3 % (keeping plant cover and temperature the same), recalculated the biogenic emissions and repeated the base case simulations with the new biogenic emissions. The impact on photolysis rates for all three scenarios was an increase (in 2010 compared to 1990) of 3–6 % which resulted in daytime (10:00–18:00 Local Mean Time – LMT) mean surface ozone differences of 0.2–0.7 ppb (0.5–1.5 %), with the largest hourly difference rising as high as 4–8 ppb (10–16 %). The effect of changes in BVOC emissions on daytime mean surface ozone was much smaller (up to 0.08 ppb, ∼ 0.2 %), as isoprene and terpene (monoterpene and sesquiterpene) emissions increased only by 2.5–3 and 0.7 %, respectively. Overall, the impact of the SSR changes on surface ozone was greater via the effects on photolysis rates compared to the effects on BVOC emissions, and the sensitivity test of their combined impact (the combination of PHOT3 and BIO is denoted as the COMBO scenario) showed nearly additive effects. In addition, all the sensitivity runs were repeated on a second base case with increased NOx emissions to account for any potential underestimation of modeled ozone production; the results did not change significantly in magnitude, but the spatial coverage of the effects was profoundly extended. Finally, the role of the aerosol–radiation interaction (ARI) changes in the European summer surface ozone trends was suggested to be more important when comparing to the order of magnitude of the ozone trends instead of the total ozone concentrations, indicating a potential partial damping of the effects of ozone precursor emissions' reduction.

Download Full-text