Assessing surface ozone risk to human health and forests over time in Poland

Hourly ground-level ozone (O-3) data from 52 monitoring stations in Poland were analyzed over a ten-year pre-COVID19 period (2010-2019) to map and define areas at risk for human health and vegetation, and to calculate trends over the study period. Annual O3 metrics (24-h average concentrations, 50th percentiles, and hourly maxima), human health metrics (Sum Of daily maximum 8-h Means Over 35 ppb, SOMO35, summertime average of the daily 8-h maximum O-3 concentrations, O-3 MDA8, and number of daily maximum 8-h values above 60 ppb, EU60) and vegetation exposure metrics (AOT40, i.e., accumulation of hourly O3 concentrations exceeding 40 ppb during the growing season for agricultural crops AOT40c and forests AOT40f) were investigated. Higher O3 levels occurred in rural areas than in cities. Between 2010 and 2019, the O3 levels were rising in both urban and rural areas. Despite the reduction of nitrogen oxides (NOx: -2.33% year-1) and volatile organic compounds emissions (VOCs: -0.95% year(-1)), annual O-3 mean levels (+0.81 and +0.12% year(-1)), 50th percentiles (+1.06 and similar to 0% year(-1)), hourly maxima (-0.10 and +0.23% year-1), SOMO35 (+2.86 and +1.50% year(-1)), summertime O3 MDA8 (+0.49 and +0.48% year(-1)), EU60 (+0.09 and +0.15 days year(-1)), AOT40c (+3.79 and +3.29% year(-1)) and AOT40f (+4.47 and +4.34% year(-1)) commonly increased in urban and rural stations. The O3 levels increased at 75.0% of urban stations and 62.5% of rural stations. A slight decline of the number of O3 peaks occurred in cities, likely driven by the recent reductions in NOx emissions by on-road transport. For all metrics, the increase can be attributed to higher regional photochemical O3 formation and rising background O-3 levels likely driven by imported O-3 and its precursors by long-range transport, climate change, and lower O-3 titration by NOx emissions decline. The failure to attain the target value for O3 for protecting vegetation and human health and vegetation persists. Southeastern Poland, where coal stoves are still used for residential heating, faces the highest O-3 risk. This study reports new information on surface O-3 levels, exceedances, and trends in Poland to develop effective policies to mitigate O-3 effects.