Tropospheric Ozone Assessment Report: Database and metrics data of global surface ozone observations

Abstract

In support of the first Tropospheric Ozone Assessment Report (TOAR) a relational database of global surface ozone observations has been developed and populated with hourly measurement data and enhanced metadata. A comprehensive suite of ozone data products including standard statistics, health and vegetation impact metrics, and trend information, are made available through a common data portal and a web interface. These data form the basis of the TOAR analyses focusing on human health, vegetation, and climate relevant ozone issues, which are part of this special feature.Cooperation among many data centers and individual researchers worldwide made it possible to build the world's largest collection of in-situ hourly surface ozone data covering the period from 1970 to 2015. By combining the data from almost 10,000 measurement sites around the world with global metadata information, new analyses of surface ozone have become possible, such as the first globally consistent characterisations of measurement sites as either urban or rural/remote. Exploitation of these global metadata allows for new insights into the global distribution, and seasonal and long-term changes of tropospheric ozone and they enable TOAR to perform the first, globally consistent analysis of present-day ozone concentrations and recent ozone changes with relevance to health, agriculture, and climate.Considerable effort was made to harmonize and synthesize data formats and metadata information from various networks and individual data submissions. Extensive quality control was applied to identify questionable and erroneous data, including changes in apparent instrument offsets or calibrations. Such data were excluded from TOAR data products. Limitations of a posteriori data quality assurance are discussed. As a result of the work presented here, global coverage of surface ozone data for scientific analysis has been significantly extended. Yet, large gaps remain in the surface observation network both in Schultz et al: Tropospheric Ozone Assessment Report Art. 58, page 2 of 26 terms of regions without monitoring, and in terms of regions that have monitoring programs but no public access to the data archive. Therefore future improvements to the database will require not only improved data harmonization, but also expanded data sharing and increased monitoring in data-sparse regions.

Regional trend analysis of surface ozone observations from monitoring networks in eastern North America, Europe and East Asia

“…parts per billion by volume) and retrieved from April to September over 2000-2014 from the TOAR database. For the summertime mean trend analysis in Section 5, these metrics are averaged across the months of April-September and are also retrieved from the TOAR database (Schultz et al, 2017). Note that when extracting DMA8 for the 6-month summertime period the value returned is the 4th highest daily 8-hour maximum of the April-September aggregation period, which aligns with the US EPA National Ambient Air Quality Standard for ozone (https://www.epa.gov/criteria-air-pollutants/ naaqs-table); but when extracting DMA8 for individual months the value is simply the monthly mean.…”

“…High values are indicative of regions with fresh emissions of nitrogen oxides, an important ozone precursor primarily emitted by fossil fuel combustion. All of these variables were made available through the TOAR database and further details on their sources are provided by Schultz et al (2017). The TOAR dataset also identifies stations that are "rural, low elevation", "rural, high elevation or mountain", and "urban" sites using an objective methodology based on satellitedetected nighttime lights, OMI tropospheric column NO 2 and population density.…”

“…Roughly one half of all stations in the database are characterized by one of these labels. For the other half, the categorization is not robust, therefore these stations are labeled as "unclassified" (Schultz et al, 2017).…”

“…Ozone metrics produced by the Tropospheric Ozone Assessment Report (Schultz et al, 2017), available at: https://doi.pangaea.de/10.1594/PANGAEA.876108.…”

“…TOAR has produced the world's largest database of surface ozone metrics from hourly observations at over 9000 sites around the globe. These ozone metrics are freely accessible for research on the global-scale impact of ozone on climate, human health and crop/ecosystem productivity (Schultz et al, 2017). Figure 1 illustrates the coverage of the TOAR surface ozone database across North America, Europe and East Asia (additional sites are available for other regions of the…”