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Atmospheric Environment 40 (2006) 3207–3218

www.elsevier.com/locate/atmosenv

Controlling influences on daily fluctuations of inhalable particlesand gas concentrations: Local versus regional and exotic

atmospheric pollutants at Puertollano, Spain

Teresa Morenoa,�, Xavier Querola, Andres Alastueya,Saul Garcıa dos Santosb, Wes Gibbonsc

aInstitute of Earth Sciences ‘‘Jaume Almera’’, CSIC, C/Lluis Sole i Sabarıs s/n, Barcelona 08028, SpainbInstitute of Health ‘‘Carlos III’’, Crta. Majadahonda-Pozuelo km 2, 28220 Majadahonda (Madrid), Spain

cAP 23075, Barcelona 08080, Spain

Received 10 October 2005; received in revised form 19 January 2006; accepted 27 January 2006

Abstract

A 12-month study of PM10 and gases in the industrial Spanish town of Puertollano reveals striking variations in

pollutant concentrations. The normal daily pollution pattern is characterised by a daily double peak for NOx and CO and

associated double trough for ozone (morning and evening), a midday atmospheric fumigation peak for SO2 and PM10

(1–2 h later in winter), and a late morning through afternoon maximum for ozone (shorter and lower in winter).

Superimposed upon this are: (1) seasonal variations, which accentuate the PM10 and SO2 mid-morning peaks in winter

(when the peak occurs later than in summer), raise NO2, ozone and background particulate levels during the summer, and

favour enhanced levels of NO during the winter; (2) local pollution spikes, particularly those associated with SO2 release

from nearby industrial sources; (3) regional atmospheric stagnation episodes, which enhance concentrations of all

pollutants and (4) intrusion of exotic pollutants, notably desert dust from North Africa. Given that air pollutants are

known adversely to influence human health, understanding and predicting such diurnal variations in concentrations of

inhalable pollutants is especially relevant to susceptible individuals such as asthmatics.

r 2006 Elsevier Ltd. All rights reserved.

Keywords: PM10; SO2; NOx; Industry; Fumigation; Spain

1. Introduction

This paper analyses a detailed air pollutiondatabase obtained over a 12-month period (No-vember 2003–October 2004) from Puertollano in

e front matter r 2006 Elsevier Ltd. All rights reserved

mosenv.2006.01.041

ing author. Tel.: +34934095410;

0012.

ess: tmoreno@ija.csic.es (T. Moreno).

Spain, a town which makes a particularly interestingsite for the study of daily variations in pollutants. Ithas the highest concentration of heavy industry incentral Spain (south of Madrid), but is a somewhatremote site, far from any motorway system or bigcity. Thus local emissions from industry are notstrongly overprinted by anthropogenic plumes fromother nearby population centres or major long-distance roads. Furthermore, it is subject to

.

ARTICLE IN PRESST. Moreno et al. / Atmospheric Environment 40 (2006) 3207–32183208

prominent regional pollution episodes during sum-mer when atmospheric conditions over Iberia trappollutants generally and enhance background con-centrations. Finally, the town is subjected to regularintrusions of exotic, silicate-rich dust derived fromAfrica, contributing to significant increases in PM10

levels, which can jump from 56 to 952 mgm�3 in amatter of hours (10.00–12.00 h, 17 March 2004;Moreno et al., 2005). The detailed case studypresented, which investigates concentration varia-tions in both gases and particulate matter, will be ofinterest to those concerned with identifying healthrisk factors linked to air pollution in the builtenvironment, particularly in towns with heavyindustry. We demonstrate that the short-termdosage (both in absolute concentration and chemi-cal composition) of air pollutants available forinhalation by individuals in Puertollano is subject togreat variation and depends on a broadly predict-able interplay between topography, climate, andlocal, regional and more far-field pollution sources.

2. Study site and instrumentation

Puertollano (708m a.s.l.) is a town with nearly50,000 inhabitants and lies in the autonomouscommunity of Castilla-La Mancha at the transitionfrom the flat agricultural country of Spain’s south-ern Meseta to the hills of the Sierra Morena, some

Fig. 1. Location map of collecting site in Puertollano, central Spain,

sources lying within the Alcudia Valley, as well as main wind direction

220 km SSE of Madrid (Fig. 1). Geomorphologi-cally, the area is characterised by east–west ridges ofPalaeozoic basement metasediments rising to over900m a.s.l. (Sierra Morena), flanked by valleys ofNeogene and Quaternary sediments and volcanicrocks (Gibbons and Moreno, 2002). The preserva-tion of carbonaceous deposits in the Permo-Carboniferous Puertollano Basin just south of thetown has stimulated an active coal industry, inaddition to which there is now a major petrochem-ical complex (Repsol Petroleo and Repsol Quımica),a fertilizer factory (Fertiberia) and two powerstations (Elcogas S.A and Central Termica dePuertollano), as illustrated in Fig. 1. These indus-trial plants lie in relatively low ground within thebroad Alcudia Valley, confined by a prominentridge to the north and the Sierra Morena mountainsto the south.

The dominant wind direction in Puertollano isfrom the WNW, with air flowing downhill along thegentle slope of the valley floor towards the east,although there are significant variations from this(Figs. 1 and 2). Northerly nighttime winds arecommon during some months, and there is atendency for a marked change of wind direction totake place during the morning after sunrise fromWNW to NNE or SE. During the study period,morning winds from the SE, i.e. from the directionof the petrochemical works, were prominent in

showing position of town and the main industrial air pollution

s registered every 15min.

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Table 1

Main industries and their emissions to the atmosphere in the

Puertollano area (data from the annual report EPER Castilla-La

Mancha, 2004)

Activity Contaminant Quantity

(kg yr�1)

Petrol refining CO2 1910 000 000

NOx 3454 000

SOx 19586 186

TSP 825674

Electric energy CO2 1150 092 000

(Gasification of coal) NOx 658776

SOx 192000

Electric energy CO2 924012 429

(Pulverised coal

combustion)

NOx 3753 800

SOx 7362 350

TSP 879000

Plastics CO2 112000 000

SOx 289000

TSP 74000

Fertilizers and organic

compounds

CO2 146074 606

NOx 312368

TSP 58886

T. Moreno et al. / Atmospheric Environment 40 (2006) 3207–3218 3209

February and the summer months. Maximum windspeeds typically occur around midday, when tem-peratures are highest and turbulent convectioncurrents strongest, whereas the early mornings arecharacterised by relatively calm conditions (Fig. 2,time is Central European Time (CET), which isGMT+1h in winter time and GMT+2h insummer time).

The air pollution recording station used for thisstudy (El Campo de Futbol de Repsol: 0410501900W,3814106400N) is sited in the entrance of a formerfootball ground in suburbs to the SE of the towncentre, WNW of the petrochemical works and apower station, and NNE of the coal mine and asecond power station. The site is on the north sideof the broad valley, so the ground rises immediatelynorthwards but is flat and open to the south, eastand west. 2004 air pollution emissions from themain industrial sources (excluding the coal mine)are given in Table 1, which demonstrates that thepetrol refinery and southern power station are thetwo major anthropogenic sources of particulatesand gases. An additional air pollution source isprovided by around 23,000 registered motor vehi-cles (77% passenger cars; 18% commercial vehicles,Spanish Statistics National Institute Data, 2003):traffic movement in the town tends to be mainlylocal as the area lies well away from any majormotorway system, and is heaviest during themorning from 10.00 to 12.00 h (CET) due tocommercial and administrative activity rather thanrush hour traffic at the beginning of the day, whichis lower in volume.

The equipment at Campo Futbol obtained dataevery 15min throughout the year on levels of PM10

using a Beta Met One BAM1020 collector with aquartz fibre filter. Additional measurements, again

every 15min, were made of SO2 (ultravioletfluorescence), NOx (chemicoluminescence), O3

(UV absorbtion and chemicoluminescence), CO(infrared absorbtion), benzene, toluene and xylene(gas chromatography), as well as atmosphericconditions (wind velocity and direction, precipita-tion, relative humidity and ambient temperature).Data coverage for the 12-month period achieved96% for particulate material, 97% for SO2 and O3,94% for NOx and 93% for CO.

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PM10, SO2, NO, NO2, NOx, O3 and CO for the 12-month study

period comparing standard Central European time (winter) and

summer Central European time (see text for discussion).

T. Moreno et al. / Atmospheric Environment 40 (2006) 3207–32183210

The origin of the particulate matter was deducedfrom atmospheric back-trajectory analysis using theHysplit model (Draxler and Rolph, 2003, withvertically modelled transport back-trajectories beingcalculated for 5 days at 500, 1500 and 2500m a.s.l),which allows detection of source areas and amountsof far-travelled pollutants present. These interpreta-tions were also coupled with information obtainedfrom TOMS-NASA and ICoD aerosol and dustsurface maps (TOMS, http://www.jwocky.gsfc.nasa.gov; DREAM ICoD, http://www.icod.org.mt/aerosol/dust, http://www.bsc.es/projects/earthscience/DREAM)and satellite images provided by the NASA SeaWIFSproject and the NRL (http://seawifs.gsfc.nasa.gov/SEAWIFS.html; http://www.nrlmry.navy.mil) todetect African dust outbreaks.

3. Daily pollution signature

Variations in pollution levels over a 24-h periodat the Puertollano site show significant diurnalincreases and decreases of pollutants, which pri-marily reflect the interplay between anthropogenicactivity and daily climatic variations in the AlcudiaValley. Fig. 3 illustrates this by averaging all CETdata on PM10, NOx, NO2, NO, O3, SO2 and COcollected every 15min during November–March(standard CET) and April–October (summerCET). Thus the typical diurnal pollution patternstarts with an early morning rise in NOx levels after06.00 h from a nocturnal background of around25 mgm�3 (winter) and 35 mgm�3 (summer) to apeak around 60 mgm�3 by 09.00 h before fallingaway rapidly to 40 mgm�3 around 11.00 h thengently decreasing until 14.00 h. Afternoon NOx

levels continue to decrease during the wintermonths, but gently increase during the summerdue to photochemical NO2 production. During theearly evening, NOx levels rise once again to form asecond peak, more prominent in winter, with alower, broader maximum spreading the pollutionacross the evening between 20.00 and 23.00 h. Thisdaily double peak pattern is mimicked by CO levels(Fig. 3), which suggests a traffic-related influence onNOx levels. However, it is important to note thatover 8000Tm of NOx were emitted from industrialsources in the Puertollano area during 2004 (EPER,2004; Table 1), a figure calculated to represent wellover 90% of total NOx emissions (Luis SuarezLasierra personal communication using CORI-NEAIR factors). Were it not for the scavengingeffect of abundant ozone (see below), NOx levels

would rise far higher during the day. Anotherinfluence of ozone on NOx levels is exhibited by NOand NO2 concentrations showing markedly differ-

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ent behaviour during winter (NO4NO2) andsummer (NOoNO2), with lower ozone levels inwinter reducing the rate at which NO can beremoved by oxidation.

In contrast to the NOx and CO diurnal signature,PM10 and SO2 levels just show one major peak (Fig.3, CET data). Levels of particulate matter begin torise around 07.00 h from a nocturnal background ofjust under 40 mgm�3 (a high value which reflects thetypically enhanced levels at the site during the day),with the increase steepening noticeably around09.00 h (summer) or 10.00 h (winter) to reach apeak during the late morning (summer: c.70 mgm�3)or early afternoon (winter: c.80 mgm�3). A drop inPM10 levels then sets in, falling to background levelsby c.16.00 h (summer) or c.17.00 h (winter). Asubdued second peak develops during the evening,more obviously during the winter months. The SO2

data show a similar late morning (summer) or earlyafternoon (winter) peak midday-peak pattern, withthe morning rise from a background of 5 mgm�3

being particularly steep after 10.00 h to reachaverage levels of over 50 mgm�3 by 12.00 h insummer, or over 40 mgm�3 by 13.00 h in winter.As with the PM data, the midday peak is followedby a marked decline over the following 3–4 h.Evening SO2 values, although lying above thoseafter midnight, remain relatively low, with nosecond peak.

These diurnal variations in PM10 and SO2 levelsare interpreted as primarily the result of anthro-pogenic activity superimposed upon the local dailyweather pattern. During the night, cold air flowsdown southwards and northwards into the AlcudiaValley from the sierras, promoting the establish-ment of a temperature inversion in the low ground,where the monitoring station is sited. Thus, by theearly morning, a relatively stable atmosphericboundary layer a few hundred metres thick trapsindustrial and traffic pollutants and initiates thedaily rise in contaminant concentrations. The linkbetween atmospheric pollutants and local industryis illustrated in Fig. 4, which demonstrates anoverall average increase in SO2 when winds areblowing from a direction between 1001 and 1701,this coinciding with the location of the petrochem-ical works (Fig. 1).

Early morning pollutants initially remain trappedat low levels in the valley, but by mid-morning solarheating of the land surface induces vertical con-vective mixing of the air, progressively breakingdown the atmospheric inversion produced during

the previous night from the ground level upwards.As initially such mixing occurs near groundlevel, the upper ‘‘lid’’ of the inversion layer remainsstable, so that industrial pollutants will tend to bedriven sideways or even downwards, further fumi-gating the air in the valley. The data indicate thatthis Hewson-type fumigation effect peaks around11–12.00 h during the summer and 13–14.00 hduring the winter (CET). During this peak pollutionperiod, levels of PM10 can be over double what theywere in the early morning, and average SO2

concentrations can be over 10 times background.Such PM10 and SO2 peaks in concentration arelikely enhanced by the industrial emissions SE oftown being carried upwards towards the town byanabatic flow and then becoming part of thefumigation process affecting the site (see SO2 levelsand wind directions in Fig. 4), mixing with mining-related dust and particles resuspended by localtraffic. The rapid decline in afternoon pollutionlevels is attributed to the re-establishment of anegative vertical temperature gradient, with turbu-lent eddies mixing the air pollutants, and the risingair from the heated land surface expanding thethickness of the boundary layer and thus dilutingcontaminants within a thicker air mixing layer.During the late afternoon, and especially aftersunset, the radiation inversion effect returns, build-ing from ground level upwards and lofting theunstable air upwards, thereby dispersing many ofthe day’s pollutants.

A typical daily ozone pattern is for stablenighttime ozone levels to be rapidly depleted withinthe inversion layer by oxidation reaction with NO.Once solar radiation has become established,morning ozone levels rebound quickly in thepresence of NO2 and VOCs. The breakdown ofVOCs, which also show a mid-morning peak, aidsozone rebound, with some of these ozone-precursorspecies, such as toluene, being particularly efficientat short-term ozone production (Na et al., 2003).Industrial NMVOC emissions at Puertollano in2004 reached 6268Tmyr�1 (EPER, 2004). O3 levelsthus take just 1 h to regain background nocturnalconcentrations, but then continue to rise rapidly,especially in the summer when levels reach a highplateau around 11.00 h (Fig. 3). Such a pattern istypical of ozone daily trends at low atmosphericelevations, with highest levels being reached whentemperatures and solar radiation are also at theirhighest. In winter, with a less potent solar influence,the diurnal plateau is not reached until early

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pattern is shown by SO2, with ESE winds blowing from the petrochemical works (Fig. 1) bearing the highest average levels of this

pollutant (32mgm�3). Individual 15-min values for SO2 measurements above 250mg SO2m�3 are also plotted to further illustrate the

positive correlation between very high levels of SO2 and winds from the SE quadrant, and the example of the late morning transient SO2

peak on the 23 September 2004. The low values for all pollutants during NNW winds coincides with a topographic gap in the northern

sierra through which cleansing winds blow from the agricultural plain lying north of Puertollano (Fig. 1). Unfortunately, such winds are

rare (0.4% of the data).

T. Moreno et al. / Atmospheric Environment 40 (2006) 3207–32183212

afternoon, and concentrations remain much lowerthan in the hot summer months.

Although ozone concentrations during the dayincrease at the same time as SO2, they do notdecrease significantly until late in the afternoon(winter) or evening (summer), coinciding with thesecond peak shown by the NOx. Ozone is formedthrough a series of chemical reactions involvingNOx and VOCs in the presence of sunlight. Themore intense the sunlight, the more NO2 istransformed into NO and ozone, whereas with little

or no solar radiation, there will be a net loss ofozone due to the ‘‘oxidation by ozone’’ reactionwith NO to form NO2 and oxygen. Such processesare born out in our data by the striking correspon-dence between NOx morning increase and O3

decrease, with the same effect occurring duringwinter evenings (Fig. 3). The lack of NOincrease during summer evenings is attributedprimarily to the presence of abundant afternoonozone, which is able to oxidise NO rapidly enoughto prevent any evening rise in its concentration.

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Finally, during the night, ozone concentrations lieat levels between 35 and 70 mgm�3 (depending onthe season) before dipping rapidly once again to theearly morning minimum.

An average level of 45 mg PM10m�3 was recorded

for the 12 months studied, with a total of 113 daysexceeding the 50 mg PM10m

�3 value set for 2005 bythe European Union (EU Directive 1999/30/EC).During some of these days in Puertollano, signifi-cant quantities of additional atmospheric pollutantswill be superimposed upon this averaged back-ground template of regular diurnal variation (Mor-eno et al., 2005). Such additions will createanomalous pollution episodes and can be classifiedinto one of three main categories: (i) local eventsproduced by a particularly well-developed inversionlayer during calm weather and/or enhanced indus-trial output; (ii) episodes linked to enhanced generalatmospheric pollution during regional stagnation ofair masses over Iberia and (iii) the arrival of exoticpollutants, notably Saharan dust from northwestAfrica, or fine, far-travelled industrial pollutantsfrom central and northern Europe. Another majorinfluence on the diurnal pollution pattern will beseasonal changes, especially in rainfall, number ofdaylight hours, and the tendency towards settled,anticyclonic conditions. The effects of such seasonalvariations are considered below, followed by thoseof superimposed pollution episodes during the 12-month study period.

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Fig. 5. Monthly average values for each hour of the day for all main po

15min over the entire 12-month study period (CO data o50% in Aug

4. Seasonal variations

With regard to climatic changes during the year,Fig. 5 separates average daily pollution levels forPM10, SO2, NO, NO2, NOx and O3 for each monthof the year. Although same general pattern isrepeated every month, some pollutants are moreobviously affected than others by the passing of theseasons, influenced by factors such as weatherconditions, population habits (holiday periods) orthe level of use of residential and occupationalheating through the year.

4.1. PM10

The mid-morning PM10 peak is most accentuatedin the winter months of November–March, whenthe nightly atmospheric inversion is enhanced byintense cold. Thus in January 2004, PM10 levelsaround 13.00 h were over five times the earlymorning background and well over double the dailylimit set by European law. This winter mid-morningpeak was so pronounced that it increased theaverage monthly PM10 level to above the 50 mgm�3

value for both January and February. In contrast,during the spring months of April and May, themid-morning peak average never exceeded thatvalue, making these 2 months the least polluted ofthe year in terms of particulate matter. The onset ofcontinental summery conditions brings hot, dry,

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llutants at the collecting site based on measurements taken every

ust and therefore deleted) (CET data).

ARTICLE IN PRESST. Moreno et al. / Atmospheric Environment 40 (2006) 3207–32183214

settled and dusty conditions to central Spain. In2004, average temperatures jumped from 15 1C inMay to 25 1C in June, and rainfall fell from4100 lm�2 in May to o5 lm�2 in June. Back-ground PM10 levels accordingly reached their high-est in July 2004, when the hourly averageconcentration went above 50 mgm�3 for almost theentire day, and the monthly average reached amaximum of 64 mgm�3. The increased amount ofdust in the atmosphere meant that the summer mid-morning peak was less elevated above backgroundthan during the winter, and occurred earlier in theday (before 13.00 h). Similar patterns continuedduring late summer, with a prolonged invasion ofSaharan dust during the first-half of September (seebelow) generally maintaining high average levels ofbackground PM10. The rapidly shortening dayduring October brought conditions back towardsthose of winter, with a declining background level ofparticulate matter punctuated by an increasinglyprominent mid-morning peak.

4.2. SO2

Levels of SO2 mimic the midday peak pattern ofthe PM10, as would be predicted from Fig. 3.Seasonal variations are once again apparent, withhigher midday peak values associated with thesummer and winter months, and lower values withspring. Similarly, the onset of thermally convectivedissipation of the morning pollution cloud occursearlier in summer (before 13.00 h) than in winter(after 13.00 h). Unlike PM10, however, averagedbackground levels of SO2 change little during theyear.

4.3. NOx and CO

Combined NOx (NO2+NO) monthly averagesare shown in Fig. 5, which illustrates how the dailydouble peak occurs throughout the year. As withthe other pollutants discussed above, springtimerecords lowest NOx levels. Background nocturnalNOx levels are at their highest in summer, both inabsolute terms and relative to the daily peaks,whereas in wintertime, the daily peaks are verypronounced due to a low background/peak ratio.Fig. 5 shows total NOx, as well as NO2 and NO, andreveals contrasting behaviour between the twopollutants. The more dominant gas throughout theyear is NO2, especially in summer when virtually allthe increase in NOx is due to elevated NO2 levels.

The rapid rise in average temperature and fall inprecipitation from May to June 2004 is recordedby a jump in NO2 levels for June (Fig. 5). Thisbuild-up in summer background NO2 is attributedto a marked slowdown in the atmosphericremoval of NO2 as aqueous aerosols (HNO3) duringcloud formation and rain out. In contrast, duringthe winter months of November–February,levels of NO during the morning exceeded those ofNO2. Also it was only during these wintermonths that NO participated strongly in the eveningNOx peak. NO concentrations did not exhibitthis second peak from April to September becausethe evening increase in NOx was virtuallyentirely NO2, due partly to higher levels ofozone in summer. CO monthly levels show similarpatterns to NOx, especially NO2, with averagehigher levels during the summer months ofJune and July (data collection for CO in Augustwas poor and is not included here). The COmonthly trend also shows the double peakbeing much more pronounced during winter(November–February), and in the case of Decem-ber, January and February with the peak at the endof the day being higher in intensity than the earlymorning one.

Our explanation for these patterns is basedprimarily on the reactive behaviour of NO oncereleased into the atmosphere, especially duringdaylight hours. Early morning, anthropogenic NOis oxidised to NO2 by reaction with backgroundozone present in the atmosphere during the night.Similarly, anthropogenic CO stimulates oxidisingreactions that produce the radical HOO, which alsoconverts NO to NO2, this reaction in additionproducing OH. OH is a potent atmospheric oxidant,which in turn reacts with volatile organic moleculesto produce organic radicals which also can oxidiseNO to NO2 (Atkinson, 1990 and 2000). Theappearance of the sun stimulates photochemicalremoval of VOC breakdown by-products such asHCHO to produce yet more oxidising radicals thatwill scavenge remaining NO and VOC (Hewitt,2001). Thus NO is eliminated by several differentreactions and oxidised to NO2. The same processesrepeat themselves during winter evenings, minus theeffect of any photochemical reactions on VOCs. Incontrast, during summer evenings, NO is eliminatedby higher levels of photochemically producedoxidants that have built up during the long dayand this does not give enough time for NO toaccumulate (Ta et al., 2004).

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4.4. Ozone

Ozone levels in Puertollano are higher thanelsewhere in Castilla-La Mancha due mainly toindustrial emission of ozone-precursor compoundssuch as NO and VOCs. In addition, ozoneconcentrations are influenced by the intensity ofsolar radiation, so that concentrations are fre-quently higher in the hot summer afternoons fromApril to September with average hourly valuesaround 100–110 mgm�3. Despite seasonal differ-ences, however, all months present the same generalpattern shown by the yearly average in Fig. 3, with arapid increase after 10.00 h, high values during theday and a rapid descent coinciding with the loss ofsunlight. This evening decrease, being linked to thewaning of sunlight, starts around 17.00 h during thewinter but is delayed until around 21.00 h in thesummer months.

5. Pollution episodes

5.1. Local pollution episodes

During the 12-month study period, there were 34days when PM10 daily averages exceeded 50 mgm�3

primarily due to local pollution sources. Such localPM10 pollution episodes during the study periodmostly occurred from January to March underbecalmed conditions. In addition to these localPM10 episodes, unusually high emissions of gaseousindustrial pollutants sometimes disrupted the nor-mal daily pollution pattern. The local origin of theparticulate matter can be surmised if there is asimultaneous increase of locally emitted gaseouspollutants such as CO, SO2 or NOx. As previouslymentioned, high SO2 values are consistently asso-ciated with winds from directions lying betweenN901 and 1701, and especially from the SE (Fig. 4),where the power stations and the petrol refineryprovide the main sources of the gas in the area(Fig. 1; Table 1). The most prominent SO2 eventduring the study period took place on the 23September, when SO2 levels reached 1849 mgm�3

(15min value, 1176 mgm�3 hourly, Fig. 4), risingfrom an average SO2 concentration of 73 mgm�3 forthat day. Such dramatic spikes in industrial SO2

emissions will have their most obvious effect whencombined with quiet atmospheric conditions duringlate morning fumigation. On the 11 January, forexample, the midday SO2 peak showed a latemorning spike of 1818 mgm�3 at a time (12:45 pm,

1335 mgm�3 hourly value) when PM10 levels werealso enhanced (276 mgm�3, 234 mgm�3 hourly va-lue). At the same time the next day the local weatherconditions were similar, with hourly PM10 levelsstaying above 200 mgm�3, but SO2 levels haddropped to just 7 mgm�3.

5.2. Regional pollution episodes

The air masses over Iberia are prone to stagna-tion, especially across the meseta of inland Spainwhere intense summer heating induces alternatingwind currents, which move towards the interiorduring the day then back to the coasts during thenight (Millan et al., 1997). Resuspended particulatematter under these recirculating conditions, com-bined with other trapped pollutants, producespollution episodes that can spread across much ofSpain (Rodrıguez et al., 2002; Querol et al., 2004).During the study period, there were 10 days whendaily average PM10 levels exceeded 50 mgm�3

during such regional episodes. A total of fiveregional episodes were identified during the 12-month study period, each lasting for an average of2–3 days. These episodes occurred mostly fromApril to September, with the worst event occurringin 20–22 September when PM10 daily averagesreached 103 mgm�3. It is during such regionalepisodes that the highest diurnal levels of PM10

and, especially SO2, are attained.

5.3. North African PM episodes

Spain is frequently visited by intrusions of desertdust introduced by winds sourcing fron NorthAfrica (Querol et al., 2001, 2004; Rodrıguez et al.,2001; Viana et al., 2002; Escudero et al., 2005). Suchexotic particles, which mostly comprise silicates,carbonates and iron oxides to which may attach arange of other pollutants, can greatly enhancebackground daily PM10 levels (Moreno et al.,2005). During the study period, 54 days recordeddaily average PM10 levels 450 mgm�3 during NorthAfrican (NAF) episodes; such days occurringduring March and June–September. The lattermonth was especially notable because during thefirst half there were no less than 12 days with NorthAfrican influence, with daily PM10 values reachingup to 142 mgm�3. However, the strongest NorthAfrican episode affecting the area occurred during22–26 July, when a low-pressure system west ofPortugal induced the advection of North African air

ARTICLE IN PRESS

Fig. 6. Example of a North African pollution episode registered

during 21–26 July 2004 in central Spain when PM10 levels

exceeded 200mgm�3, while SO2 values remained low. Back-

trajectories calculated for the 24th of July (HYSPLIT) indicate

North African air masses delivering dust from both high and

medium altitudes.

T. Moreno et al. / Atmospheric Environment 40 (2006) 3207–32183216

masses northwards. Daily PM10 levels reached up to220 mg PM10m

�3 on the 24th, the external origin ofthe particles being emphasised by the low SO2

values registered the same day (Fig. 6).

6. Conclusions and discussion

The primary objective of the case study presentedin this paper is to provide a clear and detailedexample of how daily urban pollution patterns canvary greatly over short time scales, our example

being from an industrial location with a distinctiveclimatic and orographic setting in central Spain. Aswith all urban locations throughout the world, givena modern-equipped and well-maintained monitor-ing station, daily concentration patterns and sourcesof air pollutants can be identified. In Puertollano, asite where industry has a strong influence in thelocal emissions (e.g. 90% of total NOx), this studyprovides a particularly good illustration of howlocal concentrations of anthropogenically emittedpollutants are closely linked to daily weatherpatterns. Such background patterns will be inter-rupted, sometimes dramatically, by sudden spikes inindustrial pollutant output, which can increaseconcentrations by more than an order of magnitudeover a couple of hours. Seasonal effects willmodulate the diurnal pattern over the year, as willspecific climatic events, notably (in the case of PM)regional atmospheric stagnation and/or the intru-sion of exotic pollutants such as African dusts inEurope. Although complex, this pattern is discern-able and commonly results in striking variations inpollutant concentrations over short time scalesduring the day. Variations in pollutants at Puertol-lano will also be influenced by a combination of: (i)its position in central Spain, forming a high plateausurrounded by several mountainous systems, char-acterised by cold winters and hot dry summers(Moreno et al., 2005); (ii) the local orographydominated by the Alcudia Valley where Puertollanolies and the two W–E sierras that surround it. Suchgeographical patterns will aid fumigation of thelocal anthropogenic emissions within the valley,resulting in the common reoccurrence of well-defined pollutant patterns, such as the middayPM10 and SO2 peak, and the daily double peakfor NOx typically linked to high ozone levels.

Hundreds of published epidemiological studies(e.g., see reviews of Cohen, 2003 and Brook et al.,2004) have by now demonstrated a link betweenhuman respiratory and cardiovascular diseases, andenhanced levels of common air pollutants such asPM10 and NO2 (Tsai et al., 2003), SO2 (e.g.Sheppard et al., 1980; Balmes et al., 1987; Ballesteret al., 2002) and tropospheric ozone (Devalia et al.,1998). Legal limits currently enforceable in Europedefine average daily and annual limits, and amaximum acceptable number of exceedences ofthe daily limit values, for each specific pollutant.Given the amount of evidence available, the concernis less whether air pollution causes human illness,but more on which pollutants, from which sources,

ARTICLE IN PRESST. Moreno et al. / Atmospheric Environment 40 (2006) 3207–3218 3217

and under which atmospheric conditions, do themost health damage. However, health effects onsusceptible individuals may relate less to averagelevels of exposure than to transient fluctuations inpollutant concentrations during the day. Thus a keyquestion is when are individuals most at risk,particularly those with a known susceptibility toillnesses such as asthma, attacks of which areinduced over very short time scales (D’Amato etal., 2002). In Puertollano, the worst possible airpollution scenario for a susceptible individual wouldbe an anomalously high local emission spikeoccurring during late morning fumigation of awell-developed inversion layer during a strongregional pollution episode (a pollution scenariomore common during spring–summer time). On apractical level, it would be useful to susceptibleindividuals if they could be made aware of detailedpollution levels predicted for the day, preferablyusing real-time data. Someone hyper-sensitive toPM10 or SO2, for example, would be better advisedto take exercise at least a few hours after the middaypollution peak. Thus, the analysis of detailed airpollutant databases such as the one we haveillustrated potentially allows a more refined ap-proach to the problem of atmospheric contamina-tion and human health by considering individualresponses to fluctuating pollutant dosages inhaledduring the day.

Acknowledgements

This study has been financially supported by theSpanish Ministry of the Environment and by theMinistry of Education and Science (CGL2004-05984-C07-02/CLI). The authors are indebted tothe Department of the Environment of the Castilla-La Mancha Government for their collaborationwith this study and the quality of the monitoringdata. We also particularly thank Enrique Mantilla(CEAM) for his useful comments on the manu-script. Finally the authors would like to thank theNOAA—Air Research Laboratory (Silver Spring,MD, USA), the Euro-Mediterranean Centre onInsular Coastal Dynamics (ICoD), NASA/GoddardSpace Flight Center (Maryland, USA), NRL(Monterey, USA) and the SeaWIFS Project(NASA) for the valuable information supplied bythe HYSPLIT model, TOMS, DREAM-ICoD andNAAPs maps, and the satellite images, respectively.

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