Analysis of Summer Ozone Observations at a High Mo

Authors: P Cristofanelli P di Carlo A D’ Altorio C Dari Salisburgo P Tuccella F Biancofiore P Stocchi G P Verza T C Landi A Marinoni F Calzolari R Duchi Paolo Bonasoni

Publish Date: 2013/03/01

Volume: 170, Issue: 11, Pages: 1985-1999

PDF Link

Abstract

Tropospheric ozone O3 is an important atmospheric pollutant and climate forcer The Mediterranean basin is a hotspot region in terms of shortterm O3 distribution with frequent episodes of high tropospheric O3 especially during summer To improve the characterisation of summer O3 variability in the Mediterranean area during the period 6–27 August 2009 an experimental campaign was conducted at Campo Imperatore Mt Portella CMP a high mountain site 2388 m asl located in the central Italian Apennines As deduced from analysis of atmospheric circulation the measurement site was significantly affected by air masses originating over the Mediterranean basin which affected the measurement site for 32  of the time Analysis of average values and diurnal and daytoday variability revealed that CMP O3 observations average value 600 ± 51 ppbv were comparable with measurements at other European mountain stations indicating a prevalent effect of meteorological conditions and atmospheric transport on the synoptic scale In fact only a small “reverse” diurnal variation typically characterises diurnal O3 variability because of local thermal wind circulation which sporadically favours transport of air masses rich in O3 from the foothill regions Statistical analysis of fiveday backtrajectory ensembles indicates that synopticscale airmass transport from the Mediterranean Sea usually results in decreasing O3 concentrations at CMP whereas the highest hourly O3 values are mostly associated with air masses from central continental Europe eastern Europe and northern Italy High O3 concentrations are also related to downward airmass transport from higher altitudes Comparison of insitu O3 variability with tropospheric O3 satellitebased measurements reveals similar features of the two data sets Together with the results from backtrajectory analysis this indicates that CMP measurements might usefully improve characterisation of broadscale O3 variability over the central Mediterranean basinTropospheric ozone O3 is one of the most important atmospheric gases involved in photochemical reactions and is the most important factor determining the oxidation capacity of the troposphere and air quality Jacobson 2002 Tropospheric O3 has moreover been recognised as the third most important greenhouse gas contributing to anthropogenic radiative forcing Forster et al 2007The Mediterranean basin is a hotspot region in terms of shortterm O3 distribution and related anthropogenic contributions Monks et al 2009 surface O3 concentrations have doubled in the Mediterranean basin compared with preindustrial ages UNEP and WMO 2011 Photochemical production and O3 buildup frequently occur in this region during warm weather Vautard et al 2005 In fact the Mediterranean basin is a sensitive region for occurrence of high O3 levels especially during summer because of the favourable meteorological conditions high solar radiation high temperature and light surface wind high emission of anthropogenic and natural O3 precursors and its role as a major crossroad for airmass transport Lelieveld et al 2002 Cristofanelli and Bonasoni 2009 In particular as summarized by Lolis et al 2008 anticyclonic conditions usually prevail over the Mediterranean basin during summer for a variety of reasonsAs a result of the interaction between O3 sources and airmass transport both regional and longrange and because of its variable chemical lifetime from days to a month complex spatial and temporal variations in tropospheric O3 can lead to inhomogeneous distribution of its radiative forcing Mickley et al 2004 and nonlinear effects on regional air quality West et al 2009 Thus observation of O3 variability in different regions can contribute to furnishing a more complete picture of spatial and temporal O3 features For these reasons continuous baseline O3 monitoring is a crucial activity for improving characterization of the variability of atmospheric properties in the Mediterranean troposphere In particular because mountains are often characterised by large “areas of representativeness” and by “clean” conditions such locations are often regarded as useful for studying the background conditions of the lower troposphere Henne et al 2008 Despite this and because of the challenging environmental and logistic conditions involved in performing atmospheric observations in high mountain regions insitu observations of O3 and other atmospheric compounds are still sparse in the Mediterranean region—although highaltitude measurement sites are present along the northern border of the region eg the Alpine and Carpathian regions Pyrenees only the global GAWWMO station of Monte Cimone CMN 2165 m northern Apennines Italy is operational inside the region see for instance the World Data Center for Greenhouse Gases http//dsdatajmagojp/gmd/wdcgg/ Since 1996 longterm O3 monitoring has been conducted continuously at this station Cristofanelli and Bonasoni 2009 pointed out the importance of natural processes eg stratospheretotroposphere transport mineral dust transport and anthropogenic sources eg pollution transport in determining O3 variability at high altitudes over the Mediterranean basin Together with other O3 observations conducted in the Mediterranean basin and southern Europe in the past Kouvarakis et al 2002 Nolle et al 2005 Ribas and Peñuelas 2004 Di Carlo et al 2007 the observations have clearly shown that the tropospheric seasonal cycle of background O3 is usually characterised by the presence of a broad spring–summer peak in this region Thus investigation of summer O3 variability is particularly important over the Mediterranean basin considering that the region is frequently affected by episodes of peak O3 increases Monks et al 2009

Keywords: