Tropospheric Ozone Assessment Report II: Analysis of global ozone distribution trends and to assess vegetation impacts

We use the TOAR-II database to explore vegetation risk from surface ozone when characterized by different concentration- and flux-based metrics for three crop species (wheat, rice and soybean) and three forest species (beech and a sensitive and tolerant tropical tree species). From analysis of up to 3363 sites of present-day (2016-2021) ozone levels, we find some differences between metrics with 64% and 90% of sites exceeding critical levels for irrigated wheat and 85% and 79% for beech for concentration- and flux-based metrics, respectively. Overall, the flux-based metric tends to suggest higher levels of risk. Metrics estimate similar global trends at up to 3242 sites for the period 2005 to 2021 with between 14% and 40% of sites showing statistically significant decreasing trends, which are most prevalent in North America (NAM), followed by Europe (EUR). We use the flux-based metric and literature-derived flux-response relationships to estimate average relative yield losses of 4.9% for irrigated wheat, and losses of relative gross annual increment of 14.3%, 19.8% and 5.9% for beech, sensitive and tolerant tropical tree species, respectively. Results for soybean and rice are inconclusive. Future research should extend the TOAR database in Asia (AS), Africa and Latin America and improve flux-based methodologies. This article is part of the theme issue 'Tropospheric Ozone Assessment Report II'.