Multi-decadal surface ozone trends at globally distributed remote locations

Abstract

Extracting globally representative trend information from lower tropospheric ozone observations is extremely difficult due to the highly variable distribution and interannual variability of ozone, and the ongoing shift of ozone precursor emissions from high latitudes to low latitudes. Here we report surface ozone trends at 27 globally distributed remote locations (20 in the Northern Hemisphere, 7 in the Southern Hemisphere), focusing on continuous time series that extend from the present back to at least 1995. While these sites are only representative of less than 25% of the global surface area, this analysis provides a range of regional long-term ozone trends for the evaluation of global chemistry-climate models. Trends are based on monthly mean ozone anomalies, and all sites have at least 20 years of data, which improves the likelihood that a robust trend value is due to changes in ozone precursor emissions and/or forced climate change rather than naturally occurring climate variability. Since 1995, the Northern Hemisphere sites are nearly evenly split between positive and negative ozone trends, while 5 of 7 Southern Hemisphere sites have positive trends. Positive trends are in the range of 0.5-2 ppbv decade-1 , with ozone increasing at Mauna Loa by roughly 50% since the late 1950s. Two high elevation Alpine sites, discussed by previous assessments, exhibit decreasing ozone trends in contrast to the positive trend observed by IAGOS commercial aircraft in the European lower free-troposphere. The Alpine sites frequently sample polluted European boundary layer air, especially in summer, and can only be representative of lower free tropospheric ozone if the data are carefully filtered to avoid boundary layer air. The highly variable ozone trends at these 27 surface sites are not necessarily indicative of free tropospheric trends, which have been overwhelmingly positive since the mid-1990s, as shown by recent studies of ozonesonde and aircraft observations.

Statistical regularization for trend detection: an integrated approach for detecting long-term trends from sparse tropospheric ozone profiles

“…Petetin et al (2018) validated IAGOS data in the lowest troposphere over western Europe against rural monitoring sites at various elevations and concluded that those observations can be used to study the air quality in the agglomeration. Nevertheless, to reduce the influence from the strong diurnal cycle at the surface, all observations below the 950 hPa level and within 300 m of the surface were removed from the analysis (Gaudel et al, 2020).…”

Dynamic Processes Dominating Ozone Variability in Warm Seasons of 2014–2018 over the Yangtze River Delta Region, China

“…The O3 monthly anomalies are more precise than O3 monthly means because of the reducing impact of missing data. Using this method, Cooper et al (2020) and Lu et al (2020) quantified the O3 trend in 27 globally distributed remote locations and the whole China. In addition, anomalies of monthly average O3 concentration are defined as the difference between the individual monthly mean and the monthly mean of 2014-2018.…”

Exogenous application of chemicals for protecting plants against ambient ozone pollution: What should come next?

“…Concentrations of ground-level ozone (O 3 ) have increased throughout the northern hemisphere since the industrial revolution [ 1 , 2 , 3 , 4 ]. Urban, suburban, rural, and remote areas are generally exposed to elevated O 3 levels, in terms of both average and maximum concentrations, and mathematical models suggest that this environmental issue may persist over several coming decades [ 1 , 2 , 3 , 4 ].…”

“…Concentrations of ground-level ozone (O 3 ) have increased throughout the northern hemisphere since the industrial revolution [ 1 , 2 , 3 , 4 ]. Urban, suburban, rural, and remote areas are generally exposed to elevated O 3 levels, in terms of both average and maximum concentrations, and mathematical models suggest that this environmental issue may persist over several coming decades [ 1 , 2 , 3 , 4 ]. Moreover, an analysis of air quality following the lockdown imposed in global cities during the COVID-19 pandemic revealed a considerably amplified O 3 pollution in cities [ 5 ], highlighting the complexity of this environmental issue and the difficulty to reduce O 3 pollution [ 5 ].…”