It’s not just the heat and the drought: the role of ozone air pollution in the 2012 heat wave

Weather conditions which characterize heat waves (e.g. high temperatures, severe drought, increased solar radiation, stagnation of air masses, increased presence of biogenic volatile compounds) are highly conductive to the formation and persistence of photochemically-produced tropospheric ozone. However, it is the actual dose of ozone uptake through stomata rather than mere exposure that determines the ozone impact to vegetation. There are evidences that drought protects plants from ozone injury by stomatal closure, which restricts ozone influx into the leaves. Conversely, in natural ecosystems and in non-irrigated crops dry deposition of ozone, which is mainly due to stomatal absorption, is curtailed. As a consequence, during heat wave episodes more ozone is produced and less ozone is depleted by dry deposition: the positive contribute of vegetation to improve air quality fails when we need it most! So, ozone is a major risk factor for living organisms (especially human beings) during extreme summer weather conditions. In addition, ozone is a powerful greenhouse gas and its increase contributes to further air warming. The paper reports some ozone data captured in Tuscany during the summer of 2012 and the results of biomonitoring campaigns performed during the same period. More frequent (and intense) exceedances of dangerous ground level ozone thresholds would be expected in Southern Europe at the current emission levels if summer weather conditions such as those of 2003 and 2012 will become a rule in the coming decades.