Temporal and spatial distribution of tropospheric NO2 over Northeast Asia using OMI data during the years 2005–2010



AtmosphericPollutionResearch6(2015)768–777

Atm

spheric Pollution



Research www.atmospolres.com



Temporal and spatial distribution of tropospheric NO2 over Northeast Asia using OMI data during the years 2005–2010 Deok–RaeKim,Jae–BumLee,ChangKeunSong,Seung–YeonKim,Young–IlMa,Kyung–MiLee,Jun–SeokCha, Sang–DeokLee GlobalEnvironmentResearchDivision,ClimateandAirQualityResearchDepartment,NationalInstituteofEnvironmentalResearch,Incheon,SouthKorea

ABSTRACT



Thisstudyaimed to examinethe maincharacteristics of troposphericnitrogendioxide(NO2)concentrationsoverthe Northeast Asia, using the Ozone Monitoring Instrument (OMI) data from 2005 to 2010. The annual mean NO2 concentrations (AMNC) had an increasing trend mainly due to increasing NO2 emissions in China except during the 2008BeijingOlympicGamesperiod,whilethereductionpoliciesofSouthKoreaandJapanhaveledittobestagnantor decreased.ToinvestigatefurtherregionalcharacteristicsofNO2increasingtrendsinChina,wedividedourstudyarea into6geographicalregions(sectors1–6)andthenconsidering4differentsocio–economiclevels(groups1–4)among main cities in Eastern regions (sector 2 and 4) where the concentrations level is the highest in China and NO2 concentrations show continued increasing trend. Especially OMI NO2 and emissions consistently showed that metropolitan/big–sizedanddevelopedcities(group1),suchasBeijingandShanghai,hadanincreasingtrendofNO2 concentrationsuntil2007anddecreasingthereafter,whilesmall/mid–sizedanddevelopingcities(groups2and3)kept a continuous increasing trend over all periods. The seasonal change in NO2 concentrations showed the apparent increasingtrendinwinterandnosignificanttrendinsummerinallgroupsexceptforgroup1.Theseresultsindicate thatanincreaseinAMNCinNortheastAsiawasmainlyattributedtotheincreasingNO2concentrationsinwinterin groups2and3.Therefore,itstronglysuggeststheimportanceoftheNO2managementforgroups2and3toimprove airqualityintheNortheastAsia.

 Keywords:NO2,OMI,satellite,NortheastAsia,China

CorrespondingAuthor:

Sang–Deok Lee

:+82Ͳ(0)32Ͳ560Ͳ7310 :+82Ͳ(0)32Ͳ568Ͳ2042

:[email protected] 

ArticleHistory: Received:04November2014 Revised:24February2015 Accepted:24February2015

doi:10.5094/APR.2015.085 

1.Introduction  Nitrogen dioxide (NO2) is a major gas that affects the atmospheric environment and indirectly causes climate change. It adversely impacts human health, causing ozone and particulate matter (PM) in the troposphere, along with acid rain and photochemicalsmog(Vidotetal.,2010;Wangetal.,2011;Geddes etal.,2012;Bechleetal.,2013;Zyrichidouetal.,2013).Besides,in thecontextofclimatechange,itreducesthelifetimeofmethanein theatmosphere,leadingtonegativeradiativeforcing(IPCC,2007). Therefore, investigating the concentrations, the changes and emission sources of NO2 has become one of the most important environmentalissues.NO2concentrationsinthetroposphereshow high correlation with emission quantity in source area as it is mainly affected locally rather than by long–range transport because of short lifetime with just 1–2 days (Cheng et al., 2012). NO2 playsan important rolein the chemical process ofthe major chemicals in the troposphere and also affects the formation of ground–level ozone by involving the photochemical oxidation reactionswithCH4andCO(Anejaetal.,1996).Thedominantsink ofNO2inthetroposphereisitsconversionintonitricacid(HNO3) and peroxyacetylnitrate (PAN), which are eventually removed by dryorwetdeposition(Browneetal.,2013).  MajorsourcesofNO2 includeanthropogenicsources,suchas stationary sources (industrial facilities), mobile sources (vehicles, ships, airplanes), and small–scale sources (heating facilities, kitchens)andnaturalsources,suchaslightning,volcaniceruption, andbacteria(Sheeletal.,2010).Allovertheworld,variousstudies havebeenconductedintheformofsurfaceobservations,aircraft

measurements, and modeling to assess NO2 concentrations and identify emission sources (Grice et al., 2009; Anttila et al., 2011; Shonetal.,2011;Xingetal.,2011;Lietal.,2012;Tianetal.,2013). However, surface observations and aircraft measurements have spaceconstraintsthatcouldnotbeidentifiedatthesametimein the wide open area, although providing reliable data (David and Nair,2013).Modelingstudyalsohasadisadvantagetobeverified by observation, although it can cover an extensive area. Meanwhile, observation of NO2 concentrations using satellite not only overcomesspace constraints,butalsocanproduce data in a stableway.  Developed countries like the U.S. and Europe, have actively used satellites to observe NO2 concentrations. It was suggested that satellites are reliable through comparing the NO2 data from OMIwithsurfaceobservationsthatdisplayedhighcorrelationwith California (r=0.93) and Toronto (r=0.86) (Geddes et al., 2012; Bechle et al., 2013). Additionally, Zyrichidou et al. (2013) showed thatthemonthlyaverageNO2concentrationsofthemetropolitan area (2.0–5.7±1.1×1015molecules/cm2) was higher than that of rural regions (1.1–2.2±0.4×1015molecules/cm2) in Southeastern Europe. Zhou et al. (2012) pointed out the decreasing NO2 concentrations in Western Europe from 2004 to 2009 and Ghude etal.(2009)alsoshowedthedecreaseinNO2concentrationsinthe EasternU.S.(–2±1.5%1/year)andEurope(0.9±2.1%1/year)from 1996 to 2006. The NO2 concentrations in the atmosphere are increasingintheAsiarespondingthepopulationgrowthandrapid industrializationinthisregion(Kunhikrishnanetal.,2006;Laletal., 2012; Meena et al., 2013; ul–Haq et al., 2014). He et al. (2007) foundacontinuousincreaseofNO2concentrationsduringthepast

©Author(s)2015.ThisworkisdistributedundertheCreativeCommonsAttribution3.0License.

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 decade with a sharp linear increase rate of 14.1–20.5% per year during 2000–2005 in East Asia using Global Ozone Monitoring Experiment (GOME) and SCanning Imaging Absorption spectroͲ Meter for Atmospheric CHartographY (SCIAMACHY) observations. NOXemission fromcombustionofstationary sources andvehicles has significantly increased in Northeast Asia (Ohara et al., 2007). Richter et al. (2005) also showed that the largest increase in NO2 concentrations over the industrialized part of China took place from1996to2002.InBeijing,thecapitalofChina,thenumberof vehicles went up from 0.82 million in 1994 to 3.5 million in 2008 (Sun et al., 2011) and it was also reported that NO2 increased by 50% in the industrial regions in China from 1996 to 2004 (IPCC, 2013). These reports, however, did not clearly show annual changesinNO2concentrationsinNortheastAsia.Inthisstudy,we examined the temporal and spatial distribution of annual and monthly mean NO2 concentrations using OMI data. Then, we furtherassessedtheannualandmonthlymeanNO2concentrations bycomparingwiththeemissionsinventoryinNortheastAsiafrom 2005to2010. 

2.MaterialsandMethods  2.1.TheOMIobservations  OMI is loaded with the EOS–Aura satellite launched in July 2004 and is capable of resolving a 0.5–nm spectrum, while observing 270–nm to 500–nm ultraviolet and visible ray in nadir view mode (Levelt et al., 2006). UV rays channel consists of two subchannels (UV–1 and UV–2) and their wave spectrum is 270– 310nmand310–365nm,whiletheiraveragespectralresolutionis 0.42nmand0.45nm,respectively.Thevisiblechannelcovers365– 500nmandtheaveragespectralresolutionof0.63nm.Inaddition, the OMI sensor has a wide field of view of 114° and is able to observetheentireglobalsphereinadaywithaswathof2600km, passing the equator at 13:45 local time. The spatial resolution of OMIis13×24km2,enablingittoobservetracegases,suchasNO2, SO2,O3,OCIO,andBrO.  In order to observe NO2 from the OMI, Differential Optical Absorption Spectroscopy (DOAS) is deployed to estimate Slant Column Density (SCD), which can be obtained in Vertical Column Density(VCD)usingAirMassFactor(AMF)calculatedbyaradiative transfermodel(Hanetal.,2011).FordetailedinformationonNO2 algorithm, see Boersma et al. (2007) and the DOMINO (Dutch of OMI tropospheric NO2) Product Specification Document (http:// www.temis.nl/docs/OMI_NO2_HE5_1.0.2.pdf). The retrieval of tropospheric column NO2 takes into account the clear and cloudy conditions in the airmass factor derived for the simulated NO2 profiles(Bucselaetal.,2006).TroposphericNO2hasanuncertainty of 0.1×1015molecules/cm2 and it is underestimated by 15–30% (Celarieretal.,2008).  The monthly mean tropospheric NO2 column data (Level 3) from OMI were analyzed from January 2005 to December 2010 considering available periods for OMI data and emission inventories. Level 3 is the monthly DOMINO ver. 2.0 collection 3, with a cloud radiance fraction <50%, corresponding to cloud fractionsapproximately<20%,witha0.125°×0.125°gridresolution, available from the TEMIS website (http://www.temis.nl/ airpollution/no2col/no2regioomimonth_col3.php; Boersma et al., 2011)forKNMI–OMI.  2.2.Methods  In this study, as Figure 1 indicates, changes in tropospheric NO2 over the Northeast Asian regions were observed (north latitude 20–45° and east longitude 105–145°). The spatial and temporal distribution of NO2 concentrations from 2005 to 2010 wasanalyzedbyeachregion,sector,andgroupasfollows.  

Figure1.Targetdomaininthisstudy.Thebluelineindicatestheareasby regionforChina,SouthKorea,andJapan.Chinaisdividedinto6sectors and4groups(redboxisgroup1,orangeboxisgroup2,lightgreenbox is group3andblueboxisgroup4).

 First, the region was divided into three parts; (a) the whole Northeast Asia (all areas), (b) China, Japan, and South Korea (China+SouthKorea+Japan; CKJ) and (c) background area (the rest of the area except for CKJ). To investigate further regional characteristicsofNO2increasingtrendsinChina,wedivideditinto 6 geographicalregions(sectors 1–6). Because theareaofChina is muchbiggerthanothercountries,thereisahugedifferenceinNO2 levelsbyeachsector.Toinvestigatethecharacteristicsbyeachcity insectors2and4,Chinawasdividedagaininto4groups(Qiuand Liu,2011)dependingongrossdomesticproduct(GDP)(GDPisthe incomelevelofthecity)andpopulation(Table1).Citiesingroup1 issaturatedbecauseofthesloweconomicandpopulationgrowth, while cities in groups 2 and 3 still rapidly grow with steady population growth. Cities in group 4 are at the early stage of urbanization and economic growth with very little movement on theirpopulation.  Table1.ClassificationofcitiesbypopulationsizeandGDP GDPper capita (Unit:Dollar)

PopulationSize(Unit:Million) Metropolis BigCity MiddleCity SmallCity Rural (>10) (5–10) (1.5–5) (0.5–1.5) (<0.5)

>10000

a

a

b

c

c

5000–10000

a

b

c

c

d

3000–5000

b

c

c

d

d

1000–3000

c

c

d

d

d

<1000

c

d

d

d

d

a

Beijing,Shanghai b Tianjin,Nanging,Qingdao,Hangzhou,Wuhan c Jinan,Shijiazhuang,Hefei,Zhengzhou,Taizhou,Jinhua,Changde,Nanchang d Luan,Zhumadian



3.Results  3.1.NO2concentrationsoverNortheastAsia  Figure 2 shows a time series of the annual mean NO2 concentrations(AMNC)introposphereoverNortheastAsia.Inthe whole Northeast Asian regions (all areas), the AMNC showed an increase of 0.11×1015molecules/cm2 per year with 2.05– 2.61×1015molecules/cm2. In China, South Korea, and Japan (CKJ

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 area), it also showed an increase of 0.18×1015molecules/cm2 per year, with 3.99–4.91×1015 molecules/cm2. However, there was a small increase of 0.01×1015molecules/cm2 per year, with 0.77– 0.86×1015molecules/cm2 in the background area (except for the CKJarea).ItpresentsthatamajorNO2 increaseinNortheastAsia occurred in China, South Korea, and Japan rather than the backgroundarea. 

Figure2.TimeseriesofyearlymeantroposphericNO2from2005to2010 dividedintoallareas(blacksquares),CKJ(redtriangle),excludingCKJ(blue circles).Theerrorbarsindicate±1ʍ(standarddeviation).

 Figure 3 shows the spatial and temporal distribution of the tropospheric AMNC over Northeast Asia. It was mainly high over large cities, such as Beijing, Shanghai, and Hong Kong in China, Seoul and Busan in South Korea, and Tokyo in Japan. It was relativelyloweroverthebackgroundareaswherehumanactivities arerare.Inparticular,from2005to2010,highNO2concentrations appear to be spreading annually to the places surrounding a metropolis in China, indicating that high NO2 concentrations of neighboringareasarecausedbyindustrializationandurbanization fromeconomicdevelopment(Ghudeetal.,2009;Linetal.,2010).  (a)

Meanwhile,comparedto2005,theAMNCin2010wasontherise inmostpartsofChina,butJapanexperiencedanoveralldeclinein itsNO2concentrations(Figure3d).  Figure 4showsthespatialdistributionsoftheseasonalmean NO2 concentration during the 6 years (2005–2010) in Northeast Asia. The general patterns show highest in winter and lowest in summer over China, South Korea and Japan, while there is no distinguished changes in the background regions for all seasons. This can be attributed not only to the high NOX emission by the increaseoffueluseinwinter,butalsotothelongerlifetimeofNO2 inwinter(Richteretal.,2005;Unoetal.,2007;Zhangetal.,2007; vanderAetal.,2008;Ghudeetal.,2010;Sheeletal.,2010;Wang etal.,2011).  Figure 5a shows a time series of the AMNC in China, South Korea,andJapan.ChinaindicatesthelevelofNO2with4.03(±1.52) –5.23(±2.38)×1015molecules/cm2 which increases by 30% in 2010 comparedto2005.Themainreasonofthisresultseemstobethe increasing number of motor vehicles (Sun et al., 2010) and economic development (Wang et al., 2011). In addition, a total amountofNOXemissionsinChinaincreasedbyapproximately29% from 22127Gg/yr (2005) to 28523Gg/yr (2010), which was similar to a rise in NO2 concentrations, observed via satellite (Table2).InSouthKorea,theAMNCshowedthelevelofNO2with 5.23(±1.32)–5.44(±1.50)×1015 molecules/cm2, while showing the up and down pattern repeatedly in spite of a continuous decreasing trend of NOX emission from 2006 to 2009. The South Korean government has taken various measures to improve air qualityofthemetropolitanareabycontrollingtheemissionsfrom automobiles and industries. Owing to these measures, total NOX emissions decreased by 19% from 2005 (1306Gg/year) to 2010 (1061Gg/year) (Table 2). However, there was noactual decrease inNO2concentrationscorrespondingtothereducedemissions.Lee et al. (2014) showed that high NO2 concentrations in China influenced the Yellow Sea as well as South Korea. A distance (approximately 200 km) between the eastern regions of China, where the main emission sources are located, and South Korea is sufficientforlong–rangetransportwithin1–2days.Therefore,the changesintheAMNCinSouthKoreacouldbeexplainedduetothe

(b)

Figure3.ThespatialandtemporaldistributionsoftheannualmeantroposphericNO2concentrationsfromOMIoverNortheastAsia:(a)2005, (b)2006,(c)2007,(d)2008,(e) 2009,(f) 2010and(g) differencebetween2010and2005.

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 (c)

(d)

(e)

(f)

(g)

Figure3. (Continued).

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  transportedNO2fromChinahaveoffsettheeffectofreducedNOX emissionsinSouthKorea.InJapan,theAMNCshowsthelevelwith 2.56(±0.60)–3.26(±0.66)×1015molecules/cm2 and decreases by 20% in 2010 compared to 2005. From the early 2000s, Japan restricted the vehicles that emit high NOX and encouraged the registration of vehicles that emit low NOX under the NOX ReguͲ lation Act. Japan also reinforced the NOX emission load manageͲ ment in 2001. Starting in 2003, restriction on the operation of diesel vehicles in the metropolitan areas including Tokyo was expandedtowiderareas(SDI, 2011).Japanalsostartedtosupply zero or low–emission vehicles and constantly worked hard to cut NO2 emissions by improving vehicle fuel and distributing environͲ mentallyfriendlyfuels.AccordingtoTable2,theNOXemissionsin Japan showed a decrease by 15% from 2584Gg/yr (2005) to 2207Gg/yr(2008).ThetrendofNO2emissionwasconsistentwith thetrendofNO2concentrationsfromsatellitedata.  Figure 5b shows the mean NO2 concentrations for seasons (spring: March–May; summer: June–August; fall: September– 

November;winter:December–February)duringthe6years(2005– 2010) in China, South Korea, and Japan. The seasonal NO2 concentrationsoverChina,SouthKorea,andJapanwerehighestin winter and lowest in summer. In particular, Wang et al. (2011) showed emissions are 7% higher in winter than in summer in China.Meanwhile,Ghudeetal.(2010)suggestedthatdeclinedNO2 concentrations in summer turned out to be connected with precipitation in July and August during the monsoon season. The general patterns for temperature and precipitation in Northeast Asia show the highest in summer and the lowest in winter (Table 3). Precipitation in summer intensifies due to the Asian monsoon compared to the other seasons (Ha et al., 2005). Therefore, it enhances the photochemical reaction for NO2 extinction and removesNO2intheatmospherethroughwetdeposition.Insummer, highhumidityalsoaffectsthedecreaseinNO2concentrationsdue to the increased formation of OH radicals (Platt et al., 1984). The seasonal patterns for NO2 concentrations are affected by the combined effects, that is, the changes in both emissions and meteorology.

(a)

(b)

(c)

(d)

Figure4.ThespatialdistributionsoftheseasonalmeanNO2 concentrationfrom2005to2010 (a) spring,(b) summer,(c)fall,and(d) winter.

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  Overall,theincreaseinAMNCinNortheastAsiawasattributed mainly to the NO2 increase in China. Meanwhile, the AMNC was slightly decreased in South Korea and significantly decreased in Japan because of their regulations on NOX emissions. Each sector andgroupcausingtheincreaseofNO2inChinawillbeanalyzedin moredetailinSections3.2and3.3.  3.2.Regional(sectoral)NO2concentrationsinChina  SincethesizeofChinaisbiggerthanothercountries,thereisa huge difference in NO2 levels by each region. Thus, as Figure 1 shows,Chinaisdividedintosix sectorsbasedon thegeographical regionsinordertoanalyzecharacteristicsofeachregion.Figure6 illustratesatimeseriesfortheannualmeanandtheseasonalNO2 concentrationsoverthesixsectors ofChina.TheAMNCinthesix sectors (Sectors 1, 2, 3, 4, 5, and 6) are 2.32–3.22×1015, 7.28– 11.06×1015, 2.70–3.55×1015, 6.42–8.31×1015, 1.90–2.20×1015, and 2.12–2.31×1015 molecules/cm2, respectively, with sectors 2 and 4 having higher concentrations than other sectors (Figure 6a). The AMNC in these sectors recorded 3–5 times higher than other sectors.Thisiswhymetropolises,suchasBeijingandShanghai,are included in sectors 2 and 4. It presents that the increase of NO2 concentrationsoverChinaismainlycausedbytheNO2increasein these sectors. Furthermore, since industrialization and urbanization was expanded from eastern area to mid–western area,NO2concentrationsinsectors1and3,whicharecontiguous to sectors 2 and 4, gradually increased. The seasonal mean NO2 concentrations were higher in winter and relatively lower in summerinbothsectors2and4(Figure6b).  The AMNC in sector 2 increased on the annual basis, but in 2008 it had a decrease of 5% compared to 2007 (Figure 6a). In aspectofseasonalchange,itshowedaslightincreaseinspringbut showed a decrease in summer, fall, and winter. The Chinese government made effort to cut NO2 level for the Beijing Olympic Games period in 2008 by regulating emissions in Beijing and its surrounding areas (Xing et al., 2011). Xing et al. (2011) suggested thatNO2concentrationsdroppedto42%inBeijingbetweenAugust and September 2008, compared to 2007. Witte et al. (2009) and Mijling et al. (2009) also showed a decrease of 43% (August– September)and59%(August),respectively.Thisstudyhasasimilar result with the previous studies showing a decrease of 43% in August and 31% in September 2008 compared to 2007. But NO2 

levelsoverChinawentupagainafter2008andforthisreasonthe decrease of NO2 over China in 2008 is thought as a temporary phenomenonbytheemissionregulations.  3.3.City’sNO2concentrationsinChina  To investigate the characteristics of NO2 in sectors 2 and 4 that led the increase of NO2 in China, these sectors were again divided into four groups, as presented in Section 2.2. Figure 7 illustrates a time series of NO2 in each group from 2005 to 2010. The AMNC in each group (1, 2, 3, 4) was 22.88(±6.14)×1015– 28.19(±13.08)×1015,13.71(±5.01)–17.33(±5.99)×1015,11.22(±4.69)– 15.01(±6.59)×1015, and 5.07(±2.26)–7.71(±6.38)×1015 molecules/ cm2, respectively, with the group 1 showing the highest level, followedbygroups2–4(Figure7a).AlthoughtheAMNCingroup1 wasthehighestthanothergroups,itremarkablyshowedasteady increase until 2007 but a decrease thereafter. In contrast, the AMNC in groups 2 and 3 showed a steady rise. This is because groups2and3haveabiggergrowthpotentialthanthesaturated group 1. Group 4 remains in the early stage of urbanization and development, illustrating a relatively lower yet slightly elevating NO2level.Moreover,thistrendcanbeconfirmedonabasisofNOX emissionsbyeachgroupassuggestedinTable4.Table5presented annualNOXemissions fromcoal–fired power plants in2005–2007 foreachgroupinChinausingthereferenceofWangetal.(2012).A significant amount of NOX emissions comes from the coal–based powerplantswhichareapartfromcities(Prasadetal.,2012).The NOXemissionsdecreasedingroup1(3.8%,8.3%)andincreasedin group2and3(8.2–43.8%)fortheyear2007comparedtotheyear 2005.WithrespecttoNOXemissionsbyeachgroup,thetrendwas similar to that of the AMNC observed via satellite. These results presentedthatNO2increaseinChinawasmainlyattributedtothe increasingNO2concentrationsingroups2and3.  InmonthlymeanNO2concentrations,NO2concentrationsalso illustrated a typical seasonal pattern, decreasing in summer and elevatinginwinterregardlessofgroups(Figure7b).Thedifference of the AMNC between summer and winter was showed about 16.5molecules/cm2ingroup1,whileitinothergroupswassmaller (8.2–12.6molecules/cm2)thangroup1.Group1showedthehighest level,followedbygroups2–4,becauseBeijingandShanghaiwhich are industrialized cities with a high population density were includedingroup1(Kurokawaetal.,2009;Chengetal.,2012).

Table2.AnnualNOXemissiontrendsinNortheastAsiafrom2005to2010(Unit:Gg/yr) Region

2005

2006 a

China SouthKorea

2008 a

2009 a

2010

22127.13 

23824.90 

25695.66 

26968.78 











25978.70b



28523.18b

1063.98c

1014.31c

1061.20c





1330.60c

1354.70c

a

Japan

2007 a

1092.77c

a

2584 

a

2501 

a

2403 

2207 

a

Kurokawaetal.(2013) b Heetal.(2012) c NIER(2012)

 Table3.Observedmonthlymeantemperature(°C)andprecipitation(mm)inChina,SouthKoreaandJapanfrom2005to2010 Region Chinaa SouthKoreab Japanc a

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

1.4

4.3

9.9

16.4

22.3

26.2

28.4

27.6

23.3

17.9

10.3

4.0

°C

41.9

55.7

59.4

78.1

91.1

122.8

175.3

142.9

84.0

36.3

53.2

21.3

mm

–1.8

0.9

5.5

12.1

18.0

22.5

24.6

26.0

21.7

15.7

7.5

–0.3

°C

17.1

25.5

58.4

59.2

118.4

136.0

497.8

296.5

233.6

42.8

33.6

17.3

mm

6.4

6.9

9.9

14.2

19.0

22.7

26.2

27.9

24.3

19.2

13.5

8.9

°C

69.2

82.1

63.5

46.1

88.5

54.5

89.3

122.1

122.7

109.6

106.8

106.0

mm

Chinastatisticalyearbook(Beijing,Tianjin,Shijiazhuang,Shanghai,Nanjing,Hangzhou,Hefei,Nanchang,Jinan,Zhengzhou,Wuhan) KoreaMeteorologicalAdministration(Seoul) c JapanMeteorologicalAgency(Tokyo) b

Units

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 Table4.AnnualNOXemissionstrendsineachcityofChinafrom2005to2010(Unit:Gg/yr) Group

Province/City

2005 a

2006

2007

a

2008 290a 373b 921a 586b 397a 374b 1792a 1869b 982a 872b 1601a 1844b 453a 480b 735a 730b 854a 972b 1730a 1667b

a

Beijing

291 

292 

294 

Shanghai

786a

864a

923a

Tianjin

372a

377a

373a

Jiangsu(Nanging)

1579a

1642a

1724a

Hubei(Wuhan)

796a

893a

962a

Hebei(Shijiazhuang)

1433a

1432a

1571a

Jiangxi(Nanchang)

406a

430a

445a

Hunan(Changde)

629a

711a

751a

Anhui(Hefei,Luan)

646a

720a

751a

Henan(Zhengzhou, Zhumadian)

1360a

1467a

1704a

1

2

3

3and4

2009

2010



335b



540b



414b



2064b



1071b



2081b



534b



842b



1062b



1864b

a

Kurokawaetal.(2013) Heetal.(2012)

b

 Tostudythecausesofchangesincharacteristicsofeachgroup inmoredetail,thechangesintheAMNCwasanalyzedforsummer andwinter(Figure7cand7d).Exceptforgroup1,nodistinguished changesintheAMNCwerefoundinsummer,whereastheAMNC in winter showed an increasing trend. In case of group 1, the AMNC increased from 2005 to 2007 and decreased from 2007 to 2010 in summer, whereas it was stagnated while showing the up anddownpatternsrepeatedlyinwinter.NO2concentrationsinthe winter of 2008 showed a temporary decrease in all groups comparedto2007.AsitwasmentionedinSection3.2,theresults seem to be caused by the effects of the air pollutant regulations during the Beijing Olympic Games period. These results indicate that an increase in the AMNC in China is attributed to the increasingNO2concentrationsinwinter.  Table 5. Annual NOXemissions from coal–firedpowerplantsduring 2005– 2007inChinaa(Unit:Gg/yr) Group

Province/City

2005

2006

Beijing

82.4

73.9

75.6

Shanghai

187.9

181.1

180.7

Jiangsu(Nanging)

748.8

800.2

817.0

Hubei(Wuhan) Shandong(Qingdao, Jinan) Zhejiang(Hangzhou, Taizhou,Jinhua)

796

893

962

861.3

925.4

974.8

370.6

442.2

503.6

1

2

2and3

3

a

SeasonalVariations

Figure5.Timeseriesof(a)theannualmeanNO2concentrationfrom2005 to2010inChina(redtriangle),SouthKorea(bluecircle),andJapan(Pink star)(b)themeanNO2concentrationoffourseasons(spring,summer, fall,winter)from2005to2010.Theerrorbarsindicate±1ʍ(standard deviation).

 

2007

Hebei(Shijiazhuang)

517.3

519.6

559.6

Jiangxi(Nanchang)

137.2

139.6

148.8

Hunan(Changde)

127.6

174.5

183.5

Wangetal.(2012)



4.Conclusions  Inthisstudy,spatialandtemporaldistributionoftropospheric NO2 was analyzed for six years (2005–2010) using the OMI data over Northeast Asia. To investigate the regional characteristics of increasing trends of NO2 in China, it also was divided into 6 geographicalregions(sectors1–6)andthenconsidering4different socio–economic levels (group 1–4) among main cities in Eastern region(sector2and4). 

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 Group1 Group2

200520062007200820092010 Year



Group1 Group2

200520062007200820092010 Year

 Group1

Figure6.Timeseriesof(a)theannualmeanand(b)theseasonalmeanNO2 concentrationineachsectorfrom2005to2010.Theerrorbarsindicate±1ʍ (standarddeviation).

 The annual mean NO2 concentrations (AMNC) in Northeast Asia have continuously increased. It was higher in China, South Korea,andJapanwheremanycitiesaredenselypopulatedthanin the background areas. Particularly, it went up in China except duringthe2008BeijingOlympicGamesperiod,remainedstagnant in South Korea and decreased in Japan due to the reduction policies. Sectors 2 and 4 (eastern regions) had the highest AMNC (3–5 times higher than other sectors) in China and showed the continued increasing trend of NO2 concentrations. The AMNC in group 1 (city included in the eastern regions) showed the highest level [22.88(±6.14)–28.19(±13.08)×1015molecules/cm2], followed by groups 2–4. Especially, OMI NO2 and emissions consistently showedthatmetropolitan/big–sizedanddevelopedcities(group1) such as Beijing and Shanghai had an increasing trend of NO2 concentrations until 2007 and decreasing thereafter, while small– /mid–sized and developing cities (groups 2 and 3) kept a continuous increasing trend. Meanwhile, the seasonal change in NO2 concentrations showed the apparent increasing trend in winter and no significant changes in summer in all groups except for group 1. In case of group 1, the annual mean NO2 concenͲ trationswerestagnatedinwinteranddecreasedinsummer.These results present that increasing NO2 concentrations in China is closelyrelatedtoNO2emissionsfromthedevelopmentofthesmall– andmid–sizedcitieslinkedtoeconomicdevelopmentofChina.  Therefore,thisstudyfoundthatgroups2and3haveabigger growth potential than the saturated group 1 in China and an increase in AMNC in Northeast Asia was mainly attributed to the increasing NO2 concentrations in winter in groups 2 and 3. This providestheimportanceofthemanagementforgroups2and3to improveairqualityintheNortheastAsianregion.

Group2

Group1 Group2

Figure7.TimeseriesoftroposphericNO2ineachgroupfor(a)yearlymean from2005to2010(b)monthlymeanforthesameperiod(c)seasonaltrend (summer)and(d)seasonaltrend(winter).Theerrorbarsindicate±1ʍ (standarddeviation).

Kim et al. – Atmospheric Pollution Research (APR)

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 Acknowledgments  The authors acknowledge the Ministry of Environment of KoreaforsupportingthisworkthroughtheEnvironmentResearch &DevelopmentProgram(NIER–2011–1315)andalsoacknowledge OMIteamforkindlyprovidingthesatellitedata. 

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