Analysis of European ozone trends in the period 1995–2014

Yingying Yan,Narendra Ojha,Andrea Pozzer,Jintai Lin,Jos Lelieveld

doi:10.5194/acp-18-5589-2018

Abstract

Abstract. Surface-based measurements from the EMEP and Airbase networks are used to estimate the changes in surface ozone levels during the 1995–2014 period over Europe. We find significant ozone enhancements (0.20–0.59 µg m−3 yr−1 for the annual means; P-value < 0.01 according to an F-test) over the European suburban and urban stations during 1995–2012 based on the Airbase sites. For European background ozone observed at EMEP sites, it is shown that a significantly decreasing trend in the 95th percentile ozone concentrations has occurred, especially at noon (0.9 µg m−3 yr−1; P-value < 0.01), while the 5th percentile ozone concentrations continued to increase with a trend of 0.3 µg m−3 yr−1 (P-value < 0.01) during the study period. With the help of numerical simulations performed with the global chemistry-climate model EMAC, the importance of anthropogenic emissions changes in determining these changes over background sites are investigated. The EMAC model is found to successfully capture the observed temporal variability in mean ozone concentrations, as well as the contrast in the trends of 95th and 5th percentile ozone over Europe. Sensitivity simulations and statistical analysis show that a decrease in European anthropogenic emissions had contrasting effects on surface ozone trends between the 95th and 5th percentile levels and that background ozone levels have been influenced by hemispheric transport, while climate variability generally regulated the inter-annual variations of surface ozone in Europe.

Highlights

Tropospheric ozone has detrimental effects on human health, and elevated concentrations at the surface are of concern over most of the European region (Hjellbrekke and Solberg, 2002; WHO, 2013; EEA, 2013; Lelieveld et al, 2015)
The European Monitoring and Evaluation Programme (EMEP) (93 sites) ozone and Airbase rural (246 sites) ozone are calculated based on different number of sites, the ozone trends for annual and seasonal means are similar both during daytime and at night
As the ECHAM5/MESSy Atmospheric Chemistry (EMAC) model version used here is at a coarse resolution, which is not suitable to investigate the observed contrast ozone trends among the urban, suburban, and rural stations, we focus on the analysis of ozone levels and changes over the regional background areas monitored by EMEP network in the following results

Summary

Introduction

Tropospheric ozone has detrimental effects on human health, and elevated concentrations at the surface are of concern over most of the European region (Hjellbrekke and Solberg, 2002; WHO, 2013; EEA, 2013; Lelieveld et al, 2015). The European Union (EU) Air Quality Directive sets four standards for surface ozone to reduce its impact on human health and crop yields (http://eur-lex.europa.eu/legal-content/EN/ TXT/HTML/?uri=CELEX:32008L0050&from=EN, last access: October 2017). These standards are as follows: information threshold (1 h average: 180 μg m−3), alert threshold (1 h average: 240 μg m−3), long-term objective (maximum diurnal 8 h mean: 120 μg m−3), and the target value (long-term objective that should not be exceeded more than 25 days per year, averaged over 3 years). Background ozone changes over Europe are not so clear (Wilson et al, 2012), as they are sensitive to climate conditions and intercontinental transport of O3 and its precursors, and are significant in view of tropo-

Methods

Results

Conclusion