These average results hide local variation with exceedances between these two scenarios reaching as high as 20 days in the East Midlands and eastern UK. The risks of O 3 to human health, assessed by estimating the number of days during which running 8 h mean O 3 concentrations exceeded 100 μg m −3, show that on average across the UK, there is a difference of 16 days exceedance of the threshold between the perfect sink and drought conditions. To understand the influence of variable O 3 dry deposition three different simulations were investigated during June and July: (i) actual conditions in 2006, (ii) conditions that assume a perfect vegetation sink for O 3 deposition and (iii) conditions that assume an extended drought period that reduces the vegetation sink to a minimum.
This study investigates 2006, a particularly hot and dry year during which a heat wave occurred over the summer across much of the UK and Europe. Two models that have been used for human health (the CMAQ chemical transport model) and ecosystem (the DO 3SE O 3 deposition model) risk assessment are combined to provide a powerful policy tool capable of novel integrated assessments of O 3 risk using methods endorsed by the UNECE Convention on Long-Range Transboundary Air Pollution. Under such conditions, extended drought can effectively "turn off" the O 3 vegetation sink leading to a substantial increase in ground level O 3 concentrations. This study investigates the effect of ozone (O 3) deposition on ground level O 3 concentrations and subsequent human health and ecosystem risk under hot summer "heat wave" type meteorological events.