Study on the Variation Characteristics of Haze Weather in HubeiProvince during 1980-2012

Tianxing SU,Mingfang XU,Xiang ZHOU,Zaiqiang YANG,Jijian YUAN,Haiyan ZHANG

1.Huangshi Meteorological Bureau of Hubei Province,Huangshi 435000,China;

2.Jiangsu Key Laboratory of Agricultural Meteorology,Nanjing University of Information Science&Technology,Nanjing 210044, China

Study on the Variation Characteristics of Haze Weather in HubeiProvince during 1980-2012

Tianxing SU1*,Mingfang XU1,Xiang ZHOU1,Zaiqiang YANG2,Jijian YUAN1,Haiyan ZHANG1

1.Huangshi Meteorological Bureau of Hubei Province,Huangshi 435000,China;

2.Jiangsu Key Laboratory of Agricultural Meteorology,Nanjing University of Information Science&Technology,Nanjing 210044, China

This paper,using the method of"the combination of 14 o’clock relative humidity,visibility and weather phenomena",selected haze days during 1980-2012 from 13 stations of Hubei Province,and studied years of variation characteristics of haze weather in Hubei Province.The results showed that the average annual haze days showed a fluctuant rising trend in whole from 1980 to 2012,but there were many peak value and valley value during the whole changing process;haze days of most stations showed an increasing trend,among which the stations with less than 50 d haze days had a more obvious increasing trend,and the spatial distribution of annual mean haze days had distinct inhomogeneity.Haze days of Hubei Province presented the distribution characteristics of more in autumn and winter,and less in spring and summer,in which haze days during December-January were the most, and haze days during July-August were the least.Terrain had a big impact on local haze days,piedmont leeward zones were prone to haze days,mountainous regions were just the opposite.The research suggested that we should combine different situations with different stations instead of exclusively from the mean value of multiple stations when we analyze the mean change of haze days in a broader area,to investigate the overall changing trend and the reasons.

Haze;Hubei;Spatial and temporal distribution;Terrain

W ith the rapid development of socialeconomy and the acceleration of urbanization, the pollution of atmospheric aerosol, like haze,has been increasingly serious,which has caused the growing number of visibility degradation.Before the economy opened up,during economic low-developed period,urban haze was seldom seen,thereby didn’t attract people’s attention;because of low occurrence frequency of haze weather,the quality of weather was notvery importantthen.By now,urban haze has become a common phenomenon,the occurrence of haze has been of greatsignificance in identifying urban air quality,therefore,it has been given more and more attention by all fields of society.Before 2013,domestic judgment and recognition on haze were only based on definition using relative humidity and a little bitof aberration[1],and without a unitive evaluation index,subjective factors played a decisive role,so the authenticity,continuity and comparability of haze weather observationaldata were discounted.Experts from both home and abroad made long-term climatic analysis on haze using the combination of the essence and the forming mechanism of haze,and through observational data of visibility and relative humidity,and ruling outvision obstruction from other weather phenomena,but not using surface meteorological observations,to get the haze days indirectly[2].

Foreign scholars had studied the composition of fog and haze,and climatic characteristics[3],and also did some studies on the impactof regional haze phenomena on the climate[4].In recent years,haze weather appears frequently in China,its long lasting duration and wide distribution generate great effect.Wu Dui et al.[5]made an in-depth exploration on the spatialand temporal distribution features of haze weather in mainland China.Fan Yinqi et al.[6]found that atmospheric visibility of 11 cities all showed a decreasing trend in Hebei Province during 1960-2002,seasonal difference was becoming smaller,and the falling range of summer visibility was the largest. Liao Yufang etal.[7]analyzed the variation characteristics of haze days in Hu’nan Province during 1961-2006, and came to the conclusion that since 1970s,annual haze days of Hu’nan have been increasing dramatically, extrema have been renewed constantly,the intensity increased and the range of heavy haze areas expanded. Wei Wenxiu etal.[8]drew a conclusion that the frequency distribution of haze days was closely related to the terrain of Hebei Province.Zhao Pusheng et al.[9]analyzed the haze characteristics of BTH(Beijing,Tianjin and Hebei)regions and found that monthly change of haze days in these regions showed obvious double peaks features,namely haze days of summer and winter were more than others.Jin Jun et al.[10]summarized ash haze weather characteristics of Zhejiang Province during 1960-2008,taking the case of Hangzhou City,and analyzed the causes of haze weather of Hangzhou City,the results showed that pollutant discharge was the immediate cause causing high frequency of haze weather.Tong Yaoqing et al.[11]analyzed climatic characteristics and causes of haze weather in Nanjing areas,the results indicated that haze days of6 stations in Nanjing areas had the seasonalcharacteristics of winter＞spring＞autumn＞summer,haze daysincreased obviously.Jin Limei et al.[12]studied climatic characteristics and changing rule of fog and haze days in Shanghaifrom the aspects of time and space.Liu Aijun et al.[13]analyzed climatic characteristics and causes of haze weather in Guangzhou City according to the observational data of Guangzhou Meteorological Station during 1961-2002,and concluded that annual haze days showed a rising trend in general,and interannualvariation of haze days was mostly related to air pollutantconcentration.

Currently,the study on haze climatic variation of Hubei is less.The paper studied the spatial distribution characteristics,annual mean haze days,monthly and seasonal variation rules of haze days of Hubei Province using multiple stations data for many years,the research results provided important reference for the impact of climatic change and urban developmentto Hubeihaze.

Materials

Handling method of materials

The study used 14 o’clock observationaldata,visibility and relative humidity were less than 10.0 km and 90%,respectively,14 o’clock weather phenomena codes were 01,02,03, 04,05,10 and 42,which was named as a haze day.Before 1980(including 1980),the record on atmospheric visibility in the ground meteorologicalobservation had 9 levels[14-15],the details were as Table 1,since 1981,the record and compilation of visibility have adopted actual observed value (with km as a unit,has kept one decimalplace),for uniformity,the unitand decimal places of the visibility observational record of 1980 were converted to the same as 1981.

Data statistics and station selection

14 o’clock meteorologicaldata on visibility,relative humidity and weather phenomena codes from 13 stations with relative complete data and even distribution of geographic position in Hubei Province during 1980-2012 were selected,the stations were Fangxian,Laohekou,Zaoyang,Zhongxiang,Macheng,Enshi,Wufeng,Yichang,Jingzhou,Laifeng,Jiayu,Yingshan and Huangshi.Supporting materials were weather phenomena data from the ground observation monthly reportof the above stations,mainly for filling up the missing record.

Spatial and Temporal Distribution Characteristics of Haze Days in Hubei Province

Spatialdistribution of haze

Fig.1 is the geographicaldistribution chartof13 stations,covering most areas of the whole Hubei Province, including mountainous regions,piedmont,intermountain basin and plain. Wufeng station belongs to mountainous regions,Laifeng,Enshi and Fangxian stations are intermountain basin,Laohekou,Yixian and Yingshan stations are parts of piedmont areas, Zaoyang,Zhongxiang,Jingzhou, Macheng,Jiayu and Huangshistations are located in plain areas.

Haze days of 13 stations during 1980-2012 were figured out as Table 1,the distribution interval of annual mean haze days was 1.8-100.1 d, Fangxian’s haze days were the least, conversely,the mostwas Yichang,the gap was even more than 56 times,all indicated that the spatialdistribution of haze days in Hubei Province had evident unevenness.For others,annual mean haze days of Fangxian and Wufeng were less than 5 d;Macheng, Jingzhou,Jiayu and Yingshan’s annual mean haze days were among 5-20 d;Zaoyang,Zhongxiang and Enshi’s annual mean haze days were among 20-50 d;annual mean haze days of Laohekou,Yichang,Laifeng and Huangshi were more than 50 d, especially for Laohekou and Yichang, the annualmean haze days were 92.6 and 100.1 d,respectively,namely more than 1/4 days in one year.

The variation of annual mean haze days

Fig.2 is the variation curve of annualmean haze days of 13 stations in HubeiProvince,and the mean value of the whole province was 35.9 d,haze days showed a fluctuant rising trend in whole from 1980 to 2012,linear rising rate was 0.9 d/10 a,in which there were two peaks,respectively in early 1990s and early 21st,century;three valley value were in early 1980s,late 1990s and early 21st,as wellas 2010. During 1980-1983,annualmean haze days decreased,then increased,and even had reached to 46.1 d until1991; during 1991-2001,it decreased to 30.8 d,then increased,from 2003 to2007,it basically maintained in 37-42 d;afterwards,decreased to 30.4 d in 2010,in 2012,increased to 37.2 d.

Table 1 The visibility editing mode before 1981

Because of the wide range,broad area and different terrain of whole Hubei Province,total haze days had certain regional difference,different regions also had different year evolution.Based on this,the paper discussed and classified different stations,classifying 13 stations into 4 categories:5-20,20-50,＞50 and＜5 d. Due to low probability of haze days, Fangxian and Wufeng with less than 5 haze days hadn’t been discussed in this paper.The other 3 categories curve graphs are as follows(Fig.3, Fig.4 and Fig.5):

As shown in Fig.3,in less haze stations,except for Macheng,haze days of Jingzhou,Jiayu and Yingshan stations had a linear growth trend in 33 years,the growing rate were 1.6 d/10 a,0.4 d/10 a and 3.2 d/10 a respectively,and Yingshan’s growing trend was the most obvious.Although Macheng’s haze days showed a weak linear decreasing trend in 33 years, haze days in recent 20 years had an evidentrising trend.

In relative more haze days stations(Fig.4),annual haze days of Zhongxiang and Zaoyang increased at the rate of 5.5 d/10 a and 2.6 d/10 a, respectively,after 2010,the growth was obvious;for Enshi,it decreased at the rate of 1.0 d/10 a,in recent 20 years,the decreasing trend was obvious.For extremely more haze days stations(Fig.5),Laohekou’s haze days increased rapidly at the rate of 12.8 d/10 a,but from 2003 to 2012,it declined from 177 to 25 d. Haze days of Yichang had a slowly increasing trend at the rate of 0.7 d/10 a,after 2005,its increasing trend became obvious.Huangshi and Laifeng both presented a declining rate of 6.2 d/10 a,and their most obvious periods were 1999-2003 and 1980-1993,respectively.

In conclusion,haze days increased with time in some regions of Hubei Province during 1980-2012, and parts of regions decreased with time,but most regions had an increasing trend,and less than 50 annual mean haze days had a more obvious increasing trend;for the stations with more than 50 annualmean haze days, Laohekou’s increasing trend was very obvious,but after 2003,its declining rate was also very significant;Yichang, as the most annual mean haze days, although had an increasing trend,the increasing rate was slow,especially during 1996-2004,it showed an obvious decreasing trend;Laishi and Laifeng both had a declining trend.

Therefore,combined with the analysis of Fig.1,the slow rising trend of annual mean haze days in the whole province and the appearance of peaks and valleys were generated by different contributions of more haze stations and less haze stations.Although haze days of most stations showed a rising trend,annual total haze days in these stations were less. So the contribution was relatively less; on the contrary,more haze days stations presented a declining trend or declined obviously in a certain period; the above two made the haze days in the whole province have a rising trend. In the early 1990s,most stations had peak value,and in the whole province, also had peaks;from the late 1990s to early 21stcentury,5 stations’haze days were valley value,among which Yichang showed obvious valley value, thereby the average valley value ofthe whole province came up;5-7 years after the 21stcentury,haze days of most stations began to increase,especially Laohekou and Yichang stations,then the whole province’s haze days reached the second peak;because Laohekou and Huangshias the espe-cially more haze stations remained in a low level after 2007,generating the second valley in 2010.As can be seen,the average change of haze days in the large areas can’tstartfrom the mean value of stations exclusively, we should combine with different situations of different stations and discuss the overallchange and the causes.

Table 2 The elevation and haze days distribution of13 stations in Hubei Province

Monthly and seasonal variation characteristics ofhaze

It was founded by analyzing the data that monthly and seasonal variation characteristics of haze days of 13 stations had some similarities;by summarizing monthly haze days of 13 stations in 33 years and calculating the average value,the variation of monthly mean haze days of Hubei Province was got;based on the seasons division of March,April and May as the spring,June,July and August as the summer,September,October and November as the autumn,December, January and February as the winter, the seasonalvariation of average haze days of 13 stations was reached.As shown in Fig.6a,the variation of monthly mean haze days of Hubei Province had obvious high and low value variation characteristics,namely January and December were the most haze days,even reached 6.8 and 6.4 d,respectively;February and March decreased obviously;April further decreased;during April and September, the haze days remained in less than 2 d;July and Augustwere the least,0.9-1.0 d each month;from October to January the following year,haze days increased obviously.From Fig.6b, winter was the most haze days season in HubeiProvince,reached 16.9 d,and accounted for 51.1%ofthe whole year haze days;on the contrary,summer was the least haze days season,only had 3.1 d;spring and autumn were transition seasons between more haze days and less haze days,autumn haze days were more than spring, namely 7.3 and 5.7 d,respectively. Autumn and winter haze days accounted for 73.2%of the whole province haze days.

The causes of more haze days in autumn and winter,and less haze days in spring and summer in Hubei Province were:air activity was frequent in autumn and winter,in most cases,Hubei Province was located in cold anticyclone moving south,the air was dry,air pressure was stable and wind was weak,causing the obstruction for the diffusion and dilution of ground dust and automobile exhaust, thus generated the appearance and continuation of haze days.In spring and summer,there was a lotofrain,so the air pollutants were washed away, which was notconducive to the formation ofhaze weather.

The Influence of Terrain on Haze Weather of Hubei Province

As seen from Table 2,except for Fangxian,haze days of Wufeng were the least,conversely,haze days of Laohekou and Yichang in Wushan Mountain piedmont areas were the most,and annual mean haze days were around 100 d,which was ten times of Wufeng,however,for Yingshan,also belongs to piedmont areas, haze days were only 11.3 d;the reasons were:different air pollutants degrees of different stations,and differentpiedmont locations.Based on the above,autumn and winter were the main haze seasons in Hubei Province, northwest wind was prevailing in autumn and winter,Wushan Mountain in West Hubei had blocking and weakening effect on weather system,thus eastern foothills were the"havens", because atmospheric stability was higher there,making the obstruction for the diffusion ofpollutants.Yingshan is located in southern foothills ofDabie Mountain in the northwest-southeast direction,the direction was consistent with autumn and winter weather system,and the southern foothills had not "havens"effect,so haze days of Yingshan were less than Laohekou and Yichang.Furthermore,annual mean haze days of intermountain basin stations and plain stations were basically between piedmontstations and mountainous stations.And haze days of intermountain basin stations were more than these of plain stations,because the surrounding elevation was higher than middle,thus it wasn’t conducive to the diffusion of pollutants,and plain was conducive to the diffusion.In similarterrain,the difference of haze days in different stations was connected with localcharacteristics,for example, Fangxian station,although located in intermountain basin,its urban development was mainly in agriculture, forestry and tourism,the pollutant discharge amount was relative less,so haze days were less;Huangshi station,although in plain areas,the terrain was beneficial to the diffusion of pollutants,its urban development mainly depended on heavy industry like steel, cement,etc.,therefore,haze days of Huangshiwere significantly more than other plain stations,and even more than Enshi,Laifeng,etc.

Conclusions and Prospects

(1)The annual mean haze days within Hubei Province were among 1.8-100.1 d,and the spatialdistribution had obvious unevenness.

(2)The annualmean haze days ofHubei Province were 35.9 d.The annualmean haze days showed a fluctuantrising trend in whole from 1980 to 2012,and the rising rate was 0.9 d/10 a,among which there were many peak value and valley value.

(3)Haze days of most stations within HubeiProvince presented an increasing trend during 1980-2012,and stations with less than 50 annualmean haze days had a more obvious increasing trend;for the stations with more than 50 annualmean haze days, Laohekou’s increasing trend was very obvious,but after 2003,its declining rate was also very significant;Yichang, as the most annual mean haze days, although had an increasing trend,the increasing rate was slow,especially during 1996-2004,it showed an obvious decreasing trend;Laishi and Laifeng both had a declining trend. The analysis on the average change of haze days in the large areas can’t start from the mean value of stations exclusively,we should combine with different situations of different stations and discuss the overall change and the causes.

(4)Haze days of Hubei Province presented the distribution characteristics of more in autumn and winter,and less in spring and summer,in which haze days during December-January were most,and haze days during July-August were least.The main reasons were:air pressure was stable in autumn and winter,in spring and summer,there was a lotofrain,the influence of four seasons weather on haze formation was different.

(5)Terrain had a big impacton localhaze days,piedmont leeward zones were the most haze areas,the second was intermountain basin,the following was plain,mountainous haze days were the least;haze days were also connected with local production activities.

(6)This paper,using the method of"the combination of14 o’clock relative humidity,visibility and weather phenomena",selected haze days;although it avoided inaccurate statistics of haze days by human factors,there were limit stations data due to long history,therefore,the study on weather variation characteristics of 13 stations in Hubei Province was relative less, had some limitations.Thus we need to collect more complete data and use more perfect handling methods to study in the future.

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Responsible editor:Nanling WANG

Responsible proofreader:Xiaoyan WU

*Corresponding author.E-mail:sutianxing2323@163.com

Received:November 8,2014 Accepted:January 5,2015