The global distribution and trends of ozone health-based metrics: New results from the TOAR-II Database

The first phase of the Tropospheric Ozone Assessment Report (TOAR-I), an activity of the International Global Atmospheric Chemistry Project (IGAC), provided the first comprehensive view of surface ozone’s global distribution and trends, based on all available surface ozone observations.  TOAR-I focused on a present-day period of 2010-2014, and calculated trends for a range of periods, but primarily focused on the most recent years of 2000-2014, plus long-term trends from the 1970s/1980s through 2014.  Subsequent studies of ozone trends using data after the TOAR-I cut-off of 2014, have shown a wide range of trends, both positive and negative, at monitoring sites around the world.  To keep up with the rapid changes of ozone at urban, rural and remote locations this study provides current world-wide ozone trends using observations through 2021, archived in the newly updated TOAR-II Database of Surface Observations.  Focus is placed on two ozone metrics relevant to human health impacts:  1) the annual peak of the 6-month running mean of maximum daily 8-hour average ozone; this metric is used by Global Burden of Disease (GBD) to estimate mortality due to long-term ozone exposure; 2) the number of days per year that exceed 70 ppbv, based on the maximum daily 8-hour average ozone value; this value corresponds to the primary U.S. National Ambient Air Quality Standards for ozone and is relevant to short-term ozone exposure.  Global maps will indicate the regions of the world where the potential for ozone impacts on human health are greatest (and least), and will show regions where ozone air quality is either improving or degrading.  Despite our effort to use all available surface ozone observations, large data gaps exist across many regions of the world, especially in developing nations, and GBD maps generated by data fusion will be used to identify, and to estimate ozone levels in the data-poor regions.