Analysis of ozone concentrations measured at Zavižan, Croatia\u27s highest altitude meteorological station (1594 m a.s.l.), during the spring and summer months of 1997–2000 shows that the actual new Croatian Air Quality standards are severely exceeded. Implication of this and similar findings from other elevated sites call for additional consideration of ozone behaviour at high altitudes in defining ozone standards.Analiza podataka o volumnom udjelu ozona na Zavižanu, najvišoj meteorološkoj postaji u Hrvatskoj (1594 m iznad mora) tijekom proljeća i ljeta 1997. do 2000. godine pokazuje da vrijednosti znatno prelaze granične vrijednosti za kvalitetu zraka važeće nove hrvatske Uredbe o ozonu. Dobiveni rezultati i mjerenja s drugih visinskih postaja ukazuju da potrebu razmatranja uvjeta i na visinskim postajama pri definiranju graničnih vrijednosti za kvalitetu zraka s obzirom na ozon

Glenda Šorgo

Leo Klasinc

Nenad Kezele

Tomislav Cvitaš

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Short communicationUDC 551.510.534Ozone measurements at the mountain stationZavi`an (Croatia) for 1997–2000Tomislav Cvita{1, Nenad Kezele2, Leo Klasinc2 and Glenda [orgo21 Department of Chemistry, University of Zagreb, Zagreb, Croatia2 The Ru|er Bo{kovi} Institute, Zagreb, CroatiaReceived 17 October 2007, in final form 14 December 2007Analysis of ozone concentrations measured at Zavi`an, Croatia's highestaltitude meteorological station (1594 m a.s.l.), during the spring and summermonths of 1997–2000 shows that the actual new Croatian Air Quality stan-dards are severely exceeded. Implication of this and similar findings fromother elevated sites call for additional consideration of ozone behaviour athigh altitudes in defining ozone standards.Keywords: ozone, air quality standards, tropospheric ozone1. IntroductionOzone measurements from Croatia's highest altitude mountain lodge (builtin 1927 and rebuilt in 1952) and meteorological station (founded in 1953) atZavi`an (44.817°N, 14.983°E, 1594 m a.s.l.) for 1997–2000 are reported andanalyzed. The weather at Zavi`an (Figure 1) is very harsh due to prolongedwinter conditions and heavy storms which often cause malfunction and break-down of sensitive electronic instrumentation. The station is regularly inacces-sible via road between October and May. Results of ozone measurements andresearch within the EUROTRAC and EUROTRAC–2 projects, subprojects TOR(Tropospheric Ozone Research) 1988–1996 and TOR2 from 1998–2002 using anetwork of stations over Europe showed that the measured ozone data greatlydepend both on season and location (Audiffren et al., 2003; Klasinc, 1994). Inparticular spring-time and high-altitude results proved to be highly interesting.Ozone is a secondary pollutant, i.e. it is not emitted directly into the atmo-sphere from a source, but is formed from precursors via numerous reactionsinduced by solar radiation. Thus, for the concern of rising ozone concentra-tions during the 20th century recent research showed that the cure is not assimple and easy achievable just by reducing some anthropogenic emission tothe atmosphere. Actually, it seems that at the moment we have no measuresto prevent the rise of ambient ozone concentrations during this century either.GEOFIZIKA VOL. 24 No. 2 2007In October 2006 the Clean Air Scientific Advisory Committee of the Ame-rican Environmental Protection Agency (EPA) wrote (C&N News, 2006) thatthere is no justification for retaining the current air quality standard at 0.08ppm (8-hour average) because adverse health effects can be expected duringlonger exposures at significantly lower ozone volume fractions as documentedby numerous scientific literature. However, the experience from thousands ofozone monitoring stations in the USA indicates that a simple reduction from0.080 to 0.060 ppm without a careful analysis of how often and why such limitsare exceeded would be overhasty. Therefore, the search for an optimal solutionfor the future standard has been prolonged until March 2008 (C&N News,2007). One of the irritating monitoring results is that high altitude locationswith, by all means, clean air conditions may exhibit rather, even hazardouslyhigh ozone fractions, probably caused by intrusions from the stratosphere butalso by long-range transport from polluted areas. Namely, once all 'ozone-con-suming' constituents are removed from an air package its ozone fraction be-comes stable or even rises. Results from Zavi`an, a station not included in theTOR network (Cvita{ and Kley, 1994), attracted our interest after we hadfound that ozone monitoring data at stations Puntijarka north of Zagreb at980 m and Krvavec in Slovenia at 1700 m above sea level have significantlyhigher average values than those at lower altitudes (Cvita{ et al., 2006) duringsummer. At that time Zavi`an was one of the EMEP high-altitude stations(Kova~ et al., 2003) not yet equipped with ozone monitoring instruments andit became interesting to see whether the first ozone monitoring results wouldconfirm the typical behaviour observed at other high-altitude stations.2. Results and discussionOzone was monitored at Zavi`an during four years 1997 through 2000mainly during the growth season (1 April to 30 September). The data havebeen acquired with a Dasibi 1008 AH instrument based on UV absorption and110 T. CVITA[ ET AL.: OZONE MEASUREMENTS ...Figure 1. The meteorological station at Zavi`an in winter looking westward (left, fromwww.crometeo.hr) and spring (right).converted to hourly average volume fractions prior to analysis. The instrumentwas regularly calibrated against the Dasibi 1008 PC model, or the EnvironicsSeries 100 model. The periods of time for which ozone data were collected, thenumber of validated hourly average ozone data collected (total time) with thepercentage of the total hours covered within the monitoring period (datacoverage), the number of 8-hour running averages during the period thatexceeded 60 ppb and the number of days when this limit was exceeded andfinally the number of days when the daily average ozone fraction exceeded 55ppb are given in Table 1. Both values represent the limits defined by theCroatian air quality directive (Vlada RH, 2005): 60 ppb represents the tolerat-ed limit for an 8-hour moving average, which should not be exceeded on morethan 25 days in a year, and 55 ppb represents the daily average which shouldnot be exceeded on more than 7 days in a year. Owing to difficult weather con-ditions and insufficient support the data coverage for the whole seasons Aprilthrough September (183 days) is rather poor amounting to 41, 44, 4, and 37%for the years 1997 to 2000, respectively. Ignoring the data for 1999 due to in-sufficient coverage, the measured ambient air ozone fractions were found to besignificantly higher than at low altitudes (below 500 m). The observed beha-viour was found to be similar to that at other high altitude stations Krvavec(1700 m) (Gomi{~ek, 1994) and Puntijarka (980 m) (Klasinc, 1994; Scheel et al.,1997), but not at the lower altitude mount Sr| (420 m) near DubrovnikGEOFIZIKA, VOL. 24, NO. 2, 2007, 109–116 111Table 1. Ozone measurement periods at Zavi`an from 1997 to 2000 and corresponding violations ofthe Croatian Air Quality standards.YearMonitoring period / total time(data coverage)aNo. of days (No. of hours)with j−8h > 60 ppbNo. of days withj−d > 55 ppb199711 Jun. – 25 Aug. / 1801 h(98.7 %)61 (1148) 6619989 Jul – 2 Aug / 586 h(97.7 %)13 Aug. – 8 Oct. / 1287 h(94.1 %)13 (202) 12199915 Mar. – 8 Apr. / 533 h(92.5 %)7 (84) 7200016 Feb – 9 Apr. / 1113 h(85.9 %)5 May – 8 Jun. / 813 h(96.8 %)29 Jul. – 22 Aug. / 595 h(99.2 %)27 (193) 23a total time refers to the number of validated hourly average values; data coverage refers to the percentage inwhich the total time covers the monitoring period.b a maximum of 25 days allowed with 8-hour average volume fractions j−8h > 60 ppb.c a maximum of 7 days allowed with daily average volume fractions j−d > 55 ppb.(Cvita{ et al., 2006). The main difference in behaviour is seen in the diurnalvariation of ozone fractions: in urban and suburban sites, but also in ruralsites, the diurnal variation is prominent, roughly following the variation ofsunlight, whereas at elevated sites it is hardly noticeable, ozone fractionsbeing almost constant throughout the day.The hourly ozone data for all days (except those for 17 to 19 July 1998) arepresented as a box and whiskers plot in Figure 2. The central line representsthe median, the box height covers the 25th to 75th percentile range, the112 T. CVITA[ ET AL.: OZONE MEASUREMENTS ...Figure 2. A box and whiskers plot of the Zavi`an ozone data for the period 1997–2000 (excludingthe days 17 to 19 July 1998).Figure 3. Hourly average (black circles) and 8-hour moving average (white circles) ozone volumefractions at Zavi`an for the 5-day period of 16 to 20 July 1998 showing the high-ozone episodefrom 17 to 19 July 1998. The grey bars denote night-time.whiskers the 10th to 90th percentile and all the remaining hourly values areshown as circles. It is indicative that there is actually a minimum of ozonelevels close to noontime whereas maximum values appeared at times withoutsunlight – both indicating that ozone at the Zavi`an site is not producedlocally, but rather due to transport of its precursors and ozone itself.During the days 17 to 19 July 1998 a high-ozone episode took place atZavi`an. It started from low (below 60 ppb) values in the night of 15/16 Julysteadily rising all day on 16 July right to late night on 17 July reaching values ofover 120 ppb followed by a fall and subsequent rise on 18 and again on 19 Julyas shown in Figure 3. The three maxima resemble a typical diurnal variationduring a photo-smog episode, however the time difference is 18 and less hoursrather than 24. After the three atypical days the ozone fractions kept steadilyfalling from noon on 19 July to return to »normal« approximately constantvalues of 60 ppb on 20 July. The night-time maximum and off-diurnal variationindicate clearly that the high values are not the result of local photochemicalGEOFIZIKA, VOL. 24, NO. 2, 2007, 109–116 113Table 2. Wind direction and force on the Beaufort scale for 4 days in July 1998.16 July 1998Wind17 July 1998Wind18 July 1998Wind19 July 1998WindHour Direction Force* Direction Force* Direction Force* Direction Force4 E 5 WNW 2 C 0 S 15 E 5 C 0 C 0 SW 26 E 5 NW 1 C 0 WSW 17 E 5 C 0 C 0 WSW 18 E 5 C 0 C 0 C 09 E 5 C 0 C 0 S 210 E 3 C 0 C 0 WSW 111 E 2 WNW 1 W 1 WSW 112 E 2 C 0 W 1 WSW 213 SSE 2 WNW 1 W 1 WSW 214 C 0 WNW 1 W 1 WSW 115 C 0 WNW 1 W 1 WSW 116 C 0 WNW 1 W 1 WSW 217 C 0 C 0 C 0 WSW 218 C 0 C 0 C 0 WSW 119 W 1 C 0 SW 1 C 020 W 1 C 0 SW 1 C 021 W 1 C 0 C 0 C 0* in accordance with the Beaufort scale (0–12)production, but rather of transport. Unfortunately, there are no continuous dataon wind speed and direction, for the time of monitoring: only 18 observationsper day at every hour from 4:00 to 21:00 hours in terms of 16 wind directionsand Beaufort wind force scale (0 – 12) as given in Table 2. Thus, no detailedcorrelation of ozone fractions and wind data could be made.On the other hand, we learned from earlier meteorological analyses (J.Miller, WMO, personal communication) that out of 732 clustered back-trajec-tories arriving at Zavi`an at 1600 m in 1988, 65% came from the NW originat-ing at north Greenland (11%), eastern Canada (17%), western Canada (7%)and south Greenland (30%). However, 20% of air masses did come slowly fromthe west i.e. across the Adriatic from Northern Italy and southern to westernFrance, and only 15% even slower from SE Europe (Romania and Bulgaria).Thus, it is safe to say that most air masses arrive at Zavi`an from NW. Itfollows from the hourly observations of wind direction and wind force men-tioned above (Table 2) that the excessive-ozone episode took place duringnearly calm (C) to light breeze conditions from WNW, W and WSW on July 17,18 and 19, respectively. The unusually high levels of ozone measured at Zavi-`an far from any source of ozone precursors indicate clearly that the ozone isnot produced locally. The maximum observed on 17 July close to midnight alsoproves that its origin has to be found elsewhere rather than in photochemicalproduction. It must obviously involve transport of ozone itself and of itsprecursors.The simplest explanation would be to attribute the high values to verticaltransport via stratospheric intrusions. Indeed, such effects have been wellknown, especially at high altitudes. Occasionally stratospheric ozone was foundto reach even ground level (Lisac et al., 1993; Klai} et al., 2003). However,such events are characterized by a sudden steep rise of ozone fractions wellabove 100 ppb and a subsequent drop to relatively normal conditions. Thecharacteristic conditions favouring intrusions can be seen in synoptic charts.However, without having the necessary meteorological data, we can only con-clude that the observed behaviour with clearly pronounced maxima on threeconsecutive days makes the stratospheric intrusion an unlikely cause. Theappearance of maxima hints to a photochemical production, yet the time ofday corresponding to the maxima shows that the production must have oc-curred at some distance from the monitoring site. The wind data for the threedays 17, 18 and 19 July indicate that the wind was predominantly very weakand mainly from a westerly direction. Hence the photochemical production ofozone must have taken place over the Adriatic region after the relativelystrong wind from the east had ceased on 16 July. The question on where didthe precursors of ozone come from remains open and a detailed analysis of themotion of air masses in the region is needed.The recently proposed air quality standards for ozone (Vlada RH, 2005)are based on relatively long-term averages such as daily averages or eight-hour averages as opposed to the old standards which were based on one- or114 T. CVITA[ ET AL.: OZONE MEASUREMENTS ...even half-hour average volume fractions or mass concentrations. Such a changeis immediately reflected in the treatment of high and low altitude measure-ments. In polluted areas where ozone gets completely depleted during eveningand night-time hours the long-term averages are usually lower than in moun-tainous regions. Indeed, by applying the new air quality standard to mountainstations an unexpected result is obtained: the eight-hour average exceeded the60 ppb limit for 61 days out of 76 in 1997, 13 out of 80 in 1998 and 27 out of 67in 2000. By scaling the numbers up to 183 monitoring days of the seasonrepresenting full coverage the number of violations of standards would be 147for 1997, 30 for 1998 and 74 for 2000 where the air quality standard requiresless than 25 during the whole year. The message we are getting is obviously toavoid mountain air and to stay at low altitudes, preferably within cities, if wefear ozone induced damages to our health. The daily averages give an evenworse picture. The value of 55 ppb was exceeded for 66 days out of 76 in 1997,12 days out of 80 in 1998 and 23 days out of 67 in 2000 when only a maximumof 7 days are allowed in the whole year according to the directive (Vlada RH,2005). Even in the short period of less than a month in 1999 for which we havedata (15 March to 8 April) the daily average of 55 ppb was exceeded on 7 days.3. ConclusionThe results of ambient ozone monitoring at the high altitude station Zavi-`an during the April to September season in the years 1997 to 2000 show that,in spite of poor data coverage, average ozone volume fractions are relativelyhigh, that little diurnal variation is observed and that sometimes excessive-ozone episodes can be expected.The recent Croatian air quality directive, most probably based on lowaltitude urban air data, is frequently violated. This obviously calls for reconsi-deration of the standard, or for restricting its validity to low altitude con-ditions.Midday ozone peak volume fractions get destroyed in evening traffic-ex-haust gases leading to lower average values. Modern instruments record ozonefractions sensitively and selectively, but products of ozone destruction arelikely to represent at least as much a health hazard as ozone itself. Thestandards based solely on ozone cannot be expected to faithfully represent theair quality at high altitudes with hardly any primary pollutants as well as thatin urban sites where many ozone decomposition products escaping monitoringalso affect human well being.Acknowledgement – The financial support by the Ministry of Science, Education andSports of the Republic of Croatia (grants 0098–030 and 098–0982915–2947) is gratefullyacknowledged. We also thank the Croatian Meteorological and Hydrological Service forproviding us with the wind data for the Zavi`an station. We would also like to express ourgratitude to one of the reviewers whose detailed comments helped us to improve the text.GEOFIZIKA, VOL. 24, NO. 2, 2007, 109–116 115ReferencesAudiffren, N., Duroure, C. and Le Nir, G. (2003): Statistical properties of Puy de Dôme ozonemeasurements. Comparison with urban site properties, in: TOR–2 Final Report, EUROTRAC–2ISS, GSF, Munich, Germany, pp. 59–62.C&N News (2006): Science advisers reject EPA's ozone plans, Chem. Eng. News, October 30, 34.C&N News (2007): Tighter ozone standard sought, Chem. Eng. News, February 5, 22.Cvita{, T. and Kley, D. (1994): The TOR network, EUROTRAC ISS, Garmisch-Partenkirchen,Germany.Cvita{, T., Kezele, N., Klasinc, L., and Sorgo, G. (2006): Ozone measurements on mount Sr|,Croatia, Geofizika, 23 (2), 165–171.Gomi{~ek, B. (1994): The TOR station Krvavec. In T. Cvita{ and D. Kley: The TOR network,EUROTRAC ISS, Garmisch-Partenkirchen, Germany, pp. 118–120.Klai}, Z. B., Belu{i}, D., Buli}, I. H., and Hrust, L. (2003): Mesoscale modeling of meteorologicalconditions in the lower troposphere during a winter stratospheric ozone intrusion over Zagreb,Croatia, J. Geophys. Res., 108 (D23), 4720, doi:10.1029/2003JD003878.Klasinc, L. (1994): The TOR station Puntijarka. In T. Cvita{ and D. Kley: The TOR network,EUROTRAC ISS, Garmisch-Partenkirchen, Germany, pp. 121–123.Kova~, E., Kezele, N., Cvita{, T., and Klasinc, L. (2003): Photochemical pollution indices – ananalysis of 12 EMEP stations, in: Proceedings of the 14th International Conference »AirQuality – Assessment and policy at local, regional and global scales«, Dubrovnik, Croatia,247–254, to be published in Atmos. Environ.Lisac, I., Marki, A., Tiljak, D., Klasinc, L., and Cvita{, T. (1993): Stratospheric ozone intrusionover Zagreb, Croatia, on February 6, 1990, Meteorol. Z., N. F., 2, 224–231.Scheel, H.-E., Areskoug, H., Geiss, H., Gomi{~ek, B., Granby, K., Haszpra, L., Klasinc, L., Kley,D., Laurila, T., Lindskog, A., Roemer, M., Schmitt, R., Simmonds, P., Solberg, S. and Toupan-ce, G. (1997): On the spatial distribution and seasonal variation of lower-troposphere ozoneover Europe, J. Atmos. Chem., 28, 11–28.Vlada RH (2005): Directive on ozone in air (in Croatian), Narodne novine, Zagreb, 133/2005,11151–11153.SA@ETAKMjerenja ozona na planinskoj postaji Zavi`an (Hrvatska)tijekom 1997. – 2000.Tomislav Cvita{, Nenad Kezele, Leo Klasinc i Glenda [orgoAnaliza podataka o volumnom udjelu ozona na Zavi`anu, najvi{oj meteorolo{kojpostaji u Hrvatskoj (1594 m iznad mora) tijekom prolje}a i ljeta 1997. do 2000. godinepokazuje da vrijednosti znatno prelaze grani~ne vrijednosti za kvalitetu zraka va`e}enove hrvatske Uredbe o ozonu. Dobiveni rezultati i mjerenja s drugih visinskih postajaukazuju da potrebu razmatranja uvjeta i na visinskim postajama pri definiranju gra-ni~nih vrijednosti za kvalitetu zraka s obzirom na ozon.Klju~ne rije~i: ozon, norme za kvalitetu zraka, troposferski ozonCorresponding author's address: T. Cvita{, Department of Chemistry, University of Zagreb, Horvatovac 102a,HR-10000 Zagreb, Croatia, e-mail: cvitas@chem.pmf.hr, tel: +385 1 460 6134.116 T. CVITA[ ET AL.: OZONE MEASUREMENTS ...

Mjerenja ozona na planinskoj postaji Zavižan (Hrvatska) tijekom 1997. – 2000.

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