Ozone pollution over the Arabian Gulf

31 Pages·2012·6.81 MB·English

Atmos.Chem.Phys.Discuss.,12,6331–6361,2012 Atmospheric Dis
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doi:10.5194/acpd-12-6331-2012 and Physics ss
©Author(s)2012.CCAttribution3.0License. Discussions io 12,6331–6361,2012
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Thisdiscussionpaperis/hasbeenunderreviewforthejournalAtmosphericChemistry e Ozone pollution over
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andPhysics(ACP).PleaserefertothecorrespondingfinalpaperinACPifavailable. the Arabian Gulf
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Ozone pollution over the Arabian Gulf – io
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role of meteorological conditions p Abstract Introduction
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Conclusions References
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1 2 1,2,3
L. Smoydzin , M. Fnais , and J. Lelieveld
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1Max-Planck-InstituteforChemistry,DepartmentofAtmosphericChemistry,P.O.Box3060, cu
55020Mainz,Germany ss J I
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2KingSaudUniversity,Riyadh,SaudiArabia n
3TheCyprusInstitute,CentreforEnergy,EnvironmentandWaterResearch,Nicosia,Cyprus Pa J I
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Received: 31January2012–Accepted: 18February2012–Published: 29February2012 r Back Close
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Correspondenceto: L.Smoydzin([email protected]) FullScreen/Esc
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PublishedbyCopernicusPublicationsonbehalfoftheEuropeanGeosciencesUnion. is
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The Middle East and particularly the Arabian Gulf region are characterised by highly s
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favourable conditions for O3 formation in summer. We investigated the role of mete- ion 12,6331–6361,2012
orological conditions in O formation using the WRF-chem model. The dispersion of P
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5 air pollutants strongly depends on local wind patterns, in particular the persistent low- er Ozone pollution over
levelnorth-westerlyflowknownasthesummerShamal,andrecurrentland-seabreeze the Arabian Gulf
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circulation systems.
A general finding from our simulations is that extreme pollution events, with O mix- D L.Smoydzinetal.
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ing ratios exceeding 150nmolmol , can occur regularly over the Arabian Gulf, how- u
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ever, their location and magnitude can vary widely. O mixing ratios are highest when s
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the outflow of the regions with major anthropogenic emissions along the coast is ad- n TitlePage
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vectedovertheGulf,wherepollutionplumesarecapturedintheshallowandstablema- a
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rine boundary layer allowing little ventilation. The sea-breeze circulation often causes r
onshore advection of the pollution in the afternoon, affecting the densely populated Conclusions References
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coastal regions along the western shoreline of the Gulf.
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When the pollution is transported deeper over land, O3 mixing ratios are generally isc
lower due to rapid dilution of precursor gases in the very deep convective boundary u
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layer over the desert. io
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1 Introduction er Back Close
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Enhancedlevelsofozone(O )pollutioncanbeamajorproblembydegradingairqual- FullScreen/Esc
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ity in (sub)urban and industrial areas, especially in summer when its photochemical D
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formation by the oxidation of volatile organic compounds (VOC) and catalysed by ni- c Printer-friendlyVersion
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trogen oxides (NO ), is most efficient. From satellite observations it is known that NO ss
(NO+NO ) concenxtrations in the Arabian Gulf area are exceptionally high (Stavrakoux ion InteractiveDiscussion
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25 et al., 2008; van der A et al., 2008; Lelieveld et al., 2009). Mean concentrations of tro- ap
pospheric NO columns exceed 10×1015moleccm−2 along the northern and western e
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coast of the Arabian Gulf (Beirle et al., 2011). Analysis of data retrieved from the TES D
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satelliteinstrumentrevealthatO concentrationsareelevatedinthelowerandmidtro- c ACPD
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posphereovertheentireMiddleEast(Liuetal.,2009). Modelcalculationsindicatethat s
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the Arabian Gulf region is strongly affected by photochemical smog due to high back- n
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groundlevelsofozonebylong-distancetransport,highlyfavourableweatherconditions a
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for ozone formation and strong local pollution emissions (Lelieveld et al., 2009) e Ozone pollution over
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Ingeneral,climaticconditionsovertheArabianPeninsulainsummeraredryandhot the Arabian Gulf
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withtemperaturesregularlyexceeding35 C(ElagibandAbdu,2010). Alongthecoast
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of the Gulf, humidity is often high in the afternoon hours due to the land-sea-breeze is
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circulation (Hubert et al., 1983). u
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A frequent and persistent weather phenomenon over the Arabian Gulf in winter as sio
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wellassummerareShamalwinds(Membery,1983;Barth,2001;Raoetal.,2003;Shi
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et al., 2004). The Shamal is a low level, thermally driven northerly to northwesterly a
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flow, regularly reaching a speed of up to 30ms . During the night, the Shamal often r
weakens near the surface but strengthens at elevated levels (300–700m) (Rao et al., Conclusions References
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2003;GiannakopoulouandToumi,2011). Shamalsarethepredominantcausefordust
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outbreaks over Iraq and northern Saudi Arabia which impact visibility, air quality and is
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the radiation budget throughout the Arabian Gulf region. uss J I
During winter, Shamals are known to be initiated after the southeastward passage io
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20 of cold fronts (Perrone, 1979; Walters and Sjoberg, 1988). In summer, the semi- P J I
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permanent high pressure system over the Eastern Mediterranean, which extends into p
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northern Saudi Arabia, and a semi-permanent low pressure system over Iran lead r Back Close
to a north-westerly flow over the Arabian Peninsula and the Gulf (Rao et al., 2003). |
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Rao et al. (2003) further hypothesised that conditions under which the monsoon low D
25 over India and Pakistan extends to the lee of the Zagros mountains and the south- isc Printer-friendlyVersion
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eastern part of the Arabian Peninsula, are favourable for the outbreak of Shamals as s
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the east-west pressure gradient is increased. The Zagros mountains to the east of the io InteractiveDiscussion
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Gulf, which can exceed 2000m altitude, strongly contribute to the channelling of the P
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near surface air flow. Additionally they modulate the diurnal evolution of the Shamal pe
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through orographic flows (Giannakopoulou and Toumi, 2011). Furthermore, the land- D
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sea-breezecanmodulatetheShamalbychangesinthegeostrophicwindcomponent. c ACPD
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Particularly in summer a sea breeze regularly develops over the Arabian Gulf, s
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however over the northern coast landward penetration of marine air masses is rare, n
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whereastheycanbeadvectedmorethan200kminlandalongthesouth/south-western a
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coast (Zhu and Atkinson, 2004; Eager et al., 2008). The vertical extent of the sea e Ozone pollution over
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breeze is difficult to determine and in summer may reach an altitude of about 1.5km the Arabian Gulf
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(Zhu and Atkinson, 2004; Eager et al., 2008) with a return current above the onshore
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flow. At night the land-sea breeze over the Gulf is associated with uplift and conver- is
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gence whereas during daytime it is associated with subsidence and divergence (Zhu u
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and Atkinson, 2004). The sea breeze is initiated rather late during the day (13:00– sio
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14:00 LT) compared to other coastal areas (Eager et al., 2008). During strong Shamal
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conditions the sea breeze can be fully inhibited (Zhu and Atkinson, 2004). a
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The boundary layer over the Gulf is often very shallow and stable (Brooks and r
Rogers,2000;AtkinsonandZhu,2005;Brooksetal.,1999)ashotanddryairmasses Conclusions References
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from the surrounding deserts are advected over the cooler sea resulting in a strong
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temperature inversion and a very shallow stable layer. Since this near-surface layer is
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canformwithinanexisting,deeperboundarylayeritrepresentsan“internal”boundary uss J I
layer(Garratt,1990;Angevine,2008). IftheShamalisnottoostrong,thusallowingthe io
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20 seabreezetodevelop,theonshoreadvectionofrelativelycoolairfromtheGulftoward P J I
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the desert may also be associated with an internal boundary layer, possibly trapping p
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air pollution near the surface in the coastal region. Highly stable marine boundary r Back Close
layerssimilarlyoccure.g. overtheGulfofMaineaffectingthetransportandconcentra- |
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tions of trace gases as observed during the International Consortium for Atmospheric D
25 Research in Transport and Transformation (ICARTT)/New England Air Quality Study isc Printer-friendlyVersion
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(Angevine et al., 2006; Fehsenfeld et al., 2006). s
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The objective of this study is to assess the influence of meteorological conditions io InteractiveDiscussion
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(windregime,hightemperaturesinsummer,humidityconditions)onO formationover P
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the Arabian Gulf region. Further, we analyse the rate of photochemical O3 formation pe
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in view of uncertainties in the emission inventories of anthropogenic O precursor D
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sources. c ACPD
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2 Case study description P
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For our case studies, we have selected a period of five days in mid July (14–18) in the r
the Arabian Gulf
years2009,2010and2011. Ingeneralthepotentialforabuildupofhighconcentrations |
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ofO3ishighestinsummer(Lelieveldetal.,2009). Duringapproximatelyhalfofthetotal D L.Smoydzinetal.
of 15 days of simulation the wind direction in the boundary layer is northerly to north- is
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westerly which is the predominant flow in July based on climatological data. However, s
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the initial meteorological conditions on 14 July in all three years are rather distinct io
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(Figs.1and2)thusprovidingtheopportunitytoinvestigateO formationunderdifferent P
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ambient conditions, particularly focusing on (i) days and regions with and without the p Abstract Introduction
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development of land-sea breeze systems and (ii) periods with and without Shamal
Conclusions References
winds. |
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2.1 Synoptic conditions isc
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15 2.1.1 July 2009 ion
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Following the work of Rao et al. (2003) we have selected one simulation period p
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favourable for a persistent Shamal over the Gulf. An upper level trough was located r Back Close
over Turkey accompanied by a ridge to the west across the Eastern Mediterranean |
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and a ridge to the east over western Iran. The cyclone remained very stable over
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Turkey during the entire simulation period and propagated only slowly eastward. The is
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surfacepressuredistributionshowsasignificantnorth-southgradientovertheArabian s
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Gulf area as the Mediterranean high was strong with a ridge extending over central io InteractiveDiscussion
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Saudi Arabia (Fig. 1). Such pressure conditions typically enhance the north-westerly P
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flow near the surface (Rao et al., 2003). Compared to 2010 and 2011, wind speeds p
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overtheGulfwerehigher(maximumupto20ms ). Furthermore,thetemperatureon is
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the simulation days in 2009 was lower (regionally more than ≈5 C) than in the years u
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2010 and 2011 (Fig. 2). The temperature differences between air masses over land sio 12,6331–6361,2012
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and water were smaller leading to a higher boundary layer over water (compared to
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the years 2010 and 2011). Furthermore, meteorological conditions lead to a less effi- a
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cientorinhibitedseabreeze. AtypicalphenomenonovertheGulfisthedevelopmentof r
the Arabian Gulf
a shallow inversion only a few hundred metres above the sea surface (≈950hPa) cap-
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ping a stable and moist marine boundary layer. At approximately 500hPa a very dry
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subtropical subsidence inversion associated with the downward motion of the Hadley is
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10 circulationistypicalformostdaysinsummer(Fig.2)(AckermannandCox,1982;Reid us
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et al., 2008). io
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2.1.2 July 2010 ap Abstract Introduction
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On 14 July 2010 the 500hPa flow over the eastern Mediterranean, Iraq and Iran Conclusions References
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was almost meridional. On 15 July a weak upper level trough formed over south-
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15 ern Turkey which slightly intensified in the following days while it slowly propagated is
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north-eastward. The surface pressure chart is significantly different compared to the u
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simulationperiodin2009. AweakeningoftheIranianlow,withasimultaneousnegative io
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pressure tendency over central Saudi Arabia and the northern Gulf was unfavourable P J I
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for the development of a Shamal (Fig. 1). p
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2.1.3 July 2011
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On 14 July a cyclone was located over the Black Sea and propagated slowly south- D
eastward during the following days. Generally the surface pressure distribution was isc Printer-friendlyVersion
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similar as during the Shamal period in 2009 with a distinctive surface low over the s
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southernGulfandasouth-eastwardpenetratingMediterraneanhigh. However,aposi- io InteractiveDiscussion
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tivepressuretendencyovercentralIran,QatarandtheUAEweakenedorinhibitedthe P
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3 Model setup D
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The fully coupled chemistry version of the Weather Research and Forecasting model s
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(WRF-chem) (Grell et al., 2005) version 3.3.1 was used for this study. The treatment io 12,6331–6361,2012
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of aerosols and aerosol-cloud interactions in WRF-chem is described in detail by Fast P
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et al. (2006) and Chapman et al. (2009) and only a brief overview of the features most p
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relevant in this study is given below.
the Arabian Gulf
Gas phase chemistry is calculated using the CBMZ mechanism (Zaveri and Peters, |
1999). Direct and indirect aerosol effects are calculated in the model as described D L.Smoydzinetal.
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by Chapman et al. (2009). The representation of aerosol activation is based on the c
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parametrisation by Abdul-Razzak et al. (1998) and its implementation into WRF-chem s
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follows the description by Chapman et al. (2009) and references therein. Cloud micro- n TitlePage
physical processes are calculated using the scheme by Lin et al. (1983) with modifi- P
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cations in order to treat cloud drop numbers prognostically. For nests with horizontal e
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resolutionsrequiringtheusageofaconvectionparametrisationweusetheschemeby
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Grell and Devenyi (2002). For calculating aerosol thermodynamics and microphysics
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the Module for Simulating Aerosol Interactions and Chemistry (MOSAIC) is used (Za- D Tables Figures
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veri et al., 2008). Boundary layer physics is parametrised using the Yonsei University c
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(YSU) PBL scheme (Hong et al., 2006). ss J I
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Initialandboundaryconditionsforgasphasespeciesforoursimulationsarederived n
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from MATCH-MPIC (Model of Atmospheric Transport and Chemistry, von Kuhlmann a
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etal.,2003)whichisranoperationallyasaglobalchemicalweatherforecastingmodel er Back Close
at the Max Planck Institute for Chemistry. Initial and boundary conditions for aerosol
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constituents are taken from simulations performed with the global chemistry-climate
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model EMAC (Pringle et al., 2010). For anthropogenic emissions we use the high is
resolution(0.1×0.1◦)EDGAR-CIRCEemissioninventory(Doeringetal.,2009a)which cu Printer-friendlyVersion
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hasbeenpreparedintheframeworkoftheCIRCEProject(No. 036961)bytheEDGAR sio InteractiveDiscussion
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group(EmissionDatabaseforGlobalAtmosphericResearch)oftheEC-JointResearch
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Center Ispra (Italy), Climate Change Unit and has been evaluated by Doering et al. ap
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(2009b). r
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The setup of our simulations comprises three nests with horizontal resolutions of D
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48km, 16km and 4km and with a vertical resolution of 53 layers with narrowly spaced c ACPD
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model levels in the lower troposphere. If not mentioned otherwise we refer in our s
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analysis to the 16km grid. n
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5 4 Results er Ozone pollution over
the Arabian Gulf
4.1 O distribution and variability |
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ForouranalysiswefocusonthetimeofdaywhenO mixingratiosreachamaximum, is
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i.e. at 12:00 UTC = 15:00 Local Time (Fig. 3). A general finding from our simulations us
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encompassingatotaltimeperiodof15daysisthatO hotspotsdevelopregularlyover io
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the Arabian Gulf, however the location and the intensity of the O pollution can vary P
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widely. p Abstract Introduction
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The boundary layer over the Gulf is shallow under all conditions, being relatively
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deepest for the simulation period in 2009 (≈200–400m compared to ≈50–100m in |
2010 and 2011 around 12:00 UTC). It thus appears that the formation of O hot spots D Tables Figures
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over the Gulf is facilitated by the inhibition of vertical transport in regions with strong c
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pollutionemissions,sothatbothprecursorgasesandtheresultingO3 accumulatenear ssio J I
the surface. Especially in the year 2009 the boundary layer is relatively low over the n
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north-western part of the Gulf, which is in the region with highest VOC emissions.
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On the first day (14 July, Fig. 3, first row) of the simulation period, high O values e
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are simulated during all three years over the northern Gulf region with a distinctive hot
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spot along the coast south of Kuwait. In 2010 and 2011 O mixing ratios also exceed FullScreen/Esc
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80nmolmol further inland in the late afternoon/early evening hours (especially in is
the area of Dammam/Al Jubayl) when the sea breeze transports polluted air over the cu Printer-friendlyVersion
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coastal regions. Particularly on 14, 15 and 16 July 2010 the sea breeze is strong and s
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O mixingratiosareelevated(>60nmolmol−1)upto50–100kmwestofthecoastline. n
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On15July2010,theweakbackgroundflowfacilitatestheearlierandstrongerinitiation a
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oftheseabreeze(about08:00UTC)comparedto14July2010,leadingtothetransport r
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of marine air masses over the coast during almost the entire day. At 12:00 UTC (15 D
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July 2010) O mixing ratios over the Gulf are very low, however, almost everywhere c ACPD
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along the western coast they exceed 60nmolmol−1 (over land) with local maxima of ss
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more than 80nmolmol−1 (around 28◦N). Especially in the area of Al Jubayl O mixing n
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ratios are higher on 15 July than on 14 July because (i) the sea breeze developed a
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earlier,(ii)theboundarylayeralongthecoast(upto≈40kminland)isloweron15July er Ozone pollution over
than on 14 July, thus trapping the locally formed pollution near the surface. In contrast the Arabian Gulf
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to 2010 and 2011, on 14 July 2009 the pollution plume remains located over the sea
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during the whole day because the strong Shamal winds prevent the development of a is
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sea breeze. u
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Ontheseconddayofthesimulation(15July2009,Fig.3,secondrow)highlevelsof io
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O buildupagainoverthewesternGulfwherethepersistentnorth-westerliestransport
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the pollution emitted in Kuwait over the Gulf which contributes to the photochemical p Abstract Introduction
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transformation of local emissions further South, leading to the formation of O mixing r
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ratiosofmorethan100nmolmol . Asaconsequenceoftherareeventofaseabreeze |
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developing over the northern part of the Gulf, on 15 July 2010 the highest local mixing D Tables Figures
ratiosofO (≈120–150nmolmol−1)aresimulatedalongthecoastofKuwait. Intheyear is
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2011,O3 mixingratiosarealsoelevatedoverthenorthernGulf(≈80nmolmol−1)butin ss J I
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contrast to most other days extreme values of 100nmolmol are not exceeded. The n
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20 generalexplanationforthedistincthorizontaldistributionofsurfaceO3on15July2009, a
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2010and2011isthechangingwinddirection. In2009thewinddirectionispersistently e
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north-west,whereasitissoutherlyorsouth-easterlyin2010duringthenightandinthe
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morning. In 2011 the nighttime wind direction is also north-westerly, from Kuwait over FullScreen/Esc
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the coastal area into northern Saudi Arabia. During the time of photochemical activity
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surfaceinthatlocationarenotashighasovertheseamainlyduetothedeepboundary s
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layer(≈4.5kmintheoutflowregionsouthofKuwait)leadingtotheefficientmixingand n
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dilution of the O plume. The same argument holds for the lack of O hot spots over a
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the Gulf on 16 and 17 July in 2009 and 2010. er
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ThehorizontaldistributionofO ,especiallyintheoutflowregionofKuwaitappearsto D
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be generally very similar on 16 July, (Fig. 3 third row) in 2009 and 2011 though mixing c ACPD
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ratiosare significantlyhigher inthelatter year(≈90nmolmol versus ≈60nmolmol s
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in2009)whiletheboundarylayerheightisverysimilarinbothyears. However,in2011 n
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astableresiduallayerdevelopsinthenightbetween15and16Julyleadingtoelevated a
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O mixing ratios exceeding 60nmolmol−1 at 2000m altitude throughout the night over e Ozone pollution over
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north-eastern Saudi Arabia, facilitating long-distance transport from the north. When the Arabian Gulf
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the boundary layer develops in the morning of 16 July the elevated O mixing ratios
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from the lower free troposphere significantly contribute to the high near surface values is
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(Fig. 4, right column). u
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Asindicatedabove,theoutflowofKuwaitcancontributestronglytotheO3 formation sio
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over the Arabian Gulf. On 15 July in 2011 pollution from Kuwait is transported mainly
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overSaudiArabiaornorthwardoverIraq. DespitethelackingtransportofO precursor a
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gases from Kuwait (or more generally polluted coastal areas) over the sea, O mixing r
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15 ratios over the northern Gulf exceed 80nmolmol at 12:00 UTC. In contrast, on 16 |
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July in 2009 O mixing ratios over the Gulf are relatively low (≈40nmolmol ) even
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though the wind regime is similar as on 15 July in 2011. From Fig. 5a we can identify is
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the regions with high VOC emissions over the northern Gulf region. The O3 formation ss J I
rate between 10:00 and 12:00 UTC on 16 July 2009 in the circled region in Fig. 5a, io
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b is approximately 0.5–5 pmol(mol−1s) whereas it reaches values twice as high on P J I
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15 July 2011 (Fig. 5c), even though the emission strength of VOC’s in the area does p
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not differ between the two years. Nevertheless, in 2011 surface VOC mixing ratios are r Back Close
almost a factor of two higher in this region (200–400nmolmol−1) compared to 2009 | FullScreen/Esc
(50–100nmolmol−1). Thedifferenceisagainaconsequenceofthesubstantiallylower D
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16 July 2009 (≈100m in2011 compared to 500min 2009). In addition to less efficient s
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verticalmixingon15July2011,thewindspeedislowerthanon16July2009,andthe ion InteractiveDiscussion
reduced venting allows the buildup of high levels of O precursor gases. P
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