Abstract
This Tropospheric Ozone Assessment Report (TOAR) on the current state of knowledge of ozone metrics of relevance to vegetation (TOAR-Vegetation) reports on present-day global distribution of ozone at over 3300 vegetated sites and the long-term trends at nearly 1200 sites. TOAR-Vegetation focusses on three metrics over vegetation-relevant time-periods across major world climatic zones: M12, the mean ozone during 08:00–19:59; AOT40, the accumulation of hourly mean ozone values over 40 ppb during daylight hours, and W126 with stronger weighting to higher hourly mean values, accumulated during 08:00–19:59. Although the density of measurement stations is highly variable across regions, in general, the highest ozone values (mean, 2010–14) are in mid-latitudes of the northern hemisphere, including southern USA, the Mediterranean basin, northern India, north, north-west and east China, the Republic of Korea and Japan. The lowest metric values reported are in Australia, New Zealand, southern parts of South America and some northern parts of Europe, Canada and the USA. Regional-scale assessments showed, for example, significantly higher AOT40 and W126 values in East Asia (EAS) than Europe (EUR) in wheat growing areas (p < 0.05), but not in rice growing areas. In NAM, the dominant trend during 1995–2014 was a significant decrease in ozone, whilst in EUR it was no change and in EAS it was a significant increase. TOAR-Vegetation provides recommendations to facilitate a more complete global assessment of ozone impacts on vegetation in the future, including: an increase in monitoring of ozone and collation of field evidence of the damaging effects on vegetation; an investigation of the effects on peri-urban agriculture and in mountain/upland areas; inclusion of additional pollutant, meteorological and inlet height data in the TOAR dataset; where not already in existence, establishing new region-specific thresholds for vegetation damage and an innovative integration of observations and modelling including stomatal uptake of the pollutant.
Highlights
Tropospheric ozone is a greenhouse gas and pollutant detrimental to human health and crop and ecosystem productivity (CLRTAP, 2016; Mills and Harmens, 2011; Mills et al, 2013; Monks et al, 2015; REVIHAAP, 2013; US Environmental Protection Agency (EPA), 2013)
Data representation is greatest for North America (NAM), EUR and East Asia (EAS), with sites from these regions making up 97% of the global dataset for the three vegetation metrics
Summary and conclusions Tropospheric Ozone Assessment Report (TOAR)-Vegetation reports on the present-day global distribution of ozone at over 3300 vegetated sites across the world and long-term trends at nearly 1200 sites
Summary
Tropospheric ozone is a greenhouse gas and pollutant detrimental to human health and crop and ecosystem productivity (CLRTAP, 2016; Mills and Harmens, 2011; Mills et al, 2013; Monks et al, 2015; REVIHAAP, 2013; US EPA, 2013). Since 1990, a large portion of the anthropogenic emissions that react in the atmosphere to produce ozone have shifted from North America and Europe to Asia (Cooper et al, 2014; Granier et al, 2011; Zhang et al, 2016) This rapid shift, coupled with limited ozone monitoring in developing nations, has left scientists unable to answer the most basic questions: Which regions of the world have the greatest human and plant exposure to ozone pollution? TOAR-Vegetation, we provide an overview of the vegetation metrics available through the TOAR database, focussing on global and regional distributions and trends for three widely used metrics
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