Temporal And Spatial Variations Of Tropospheric NO₂ From Satellite Observations In Gansu Province

At present, China’s ecological environment governance is facing an unprecedented huge challenge, in which the atmospheric environmental pollution has become an important factor affecting the implementation of sustainable development strategy and environmental diplomacy.Therefore, it is of great significance to master the distribution and change of the main pollutants in the atmosphere in the early warning and control of the environment.Nitrogen dioxide（NO₂） is the main pollution gases in the atmosphere, is one of the precursors of the acid rain, photo-chemical smog and other phenomenon of serious environmental pollution.Atmospheric NO₂ concentration continuous increase is the great harm to the environment, ecological environment and human health. Gansu province is located in the northwest of China,and there is little research on the spatial and temporal distribution characteristics of NO₂ in this region, in recent years, with the rapid development of industry and economy in Gansu Province, the anthropogenic emission sources of NO₂ are increasing rapidly, and the NO₂ concentration in the atmosphere is also increasing day by day. Therefore, grasping the status of NO₂ pollution in the area, the law of temporal and spatial variation and the pollution sources is of great importance to the prevent and control air pollution and also to improve air quality.This paper uses OMINO₂ data which is interpreted by NASA EOS-ARUR satellite borne sensor OMI,through the application of VISAN software and python language to deal with the data which is stored in band format, the output, extraction,filtering and input of the NO₂ column etc. are completed,database establishment,spatial and temporal distribution map drawing and analysis are also completed.The spatial and temporal distribution characteristics and the change trend of tropospheric NO₂ column concentration in Gansu province were studied for the first time.The spatial distribution diagram and the Sinusoidal simulation diagram of the tropospheric NO₂ column concentration from 2008 to 2015 were drawn.Evaluation of air quality levels of tropospheric NO₂ column concentration in Gansu province and（prefecture）city.The results obtained are as follow:（1）Based on the spatial distribution map of the annual mean value of the tropospheric NO₂ column, the spatial distribution of NO₂ column density in Gansuprovince is obvious. With a high concentration at the center of the cluster formation,and along the central spreading around the ring, the median range appears to increase year by year and obviously contiguous trend, and low value range by compressed phenomenon, such as two high value center of Lanzhou, Baiyin respectively high value area and in Jiayuguan City, the singularity, Longnan attachment value distribution in the belt. Located in high, medium numerical with the transitional zone between the Linxia Hui Autonomous Prefecture, Dingxi City and with the second-highest value of Long Dong, northeastern border of Tianshui area, low value area is distributed in Jiuquan, Gannan Tibetan Autonomous Prefecture, which is far away from the high value center.（2）Based on the annual mean, seasonal mean and daily mean time distribution of tropospheric NO₂ column concentrations in Gansu province in 2008 ²015: From the point of view of interannual variation, the tropospheric NO₂ column of Gansu Province densities have increased year by year and began to decline trend in 2013,showing the “∩” type distribution; From the seasonal change, the concentration of NO₂ column in Gansu province has obvious seasonal characteristic, a general summer > spring > winter > autumn, regions of Lanzhou City as the representative of "winter high summer low" mode, and represented by Jiuquan City "winter low summer high" two modes; In Gansu province from the point of change, the average concentration of NO₂ column month mathematical simulations show as the sine curve,simulation precision is higher, has obvious seasonal variation law, that the area affected by human impact on weaker and less anthropogenic sources, is dominated by emissions from natural sources of regional. A typical city five months mean sine simulation results indicate different sources in different regions, including Lanzhou,Tianshui, and Qingyang City tropospheric NO₂ column concentration of human activities affect change by more intense,Jinchang City, Jiuquan City, goodness of fit is high, the actual value and the fitted values did not differ much, fitting more accurate,more obvious cyclical changes, changes in the concentration of tropospheric NO₂ column more affected by natural factors.（3）Based Correlation Analysis of tropospheric NO₂ column density and the Air Quality Index（AQI）, dividing the concentration of NO₂ column indicate air qualitypollution level in gansu province, ambient air quality in gansu province is given priority to with a good, has the certain light pollution. That is, from 2008 ²015,Gansu and its land（state） city air quality has two types, good and light pollution.Pollution levels for the good of the region accounted for more than 89.98%⁹9.56%of the area of Gansu Province, light pollution is only 0.44%¹0.02%. Most of lightly polluted areas are mainly distributed in Lanzhou City and minority of Baiyin,Pingliang, Qingyang City. For eight years, the most contaminated area hours 0.44%,the maximum 10.02% of the province area, which in 2015 in Gansu Province, under the direction of NO₂, the air quality is best. Good region accounted for 99.56%, 2011 is bad, good area of the smallest, accounting for 89.98%.（4）Based on tropospheric NO₂ column density statistical average for many years,the 14 prefectures（States） are divided into five types in Gansu Province, the first category is Lanzhou（about 6.0×1015molec/cm2）, followed Qingyang, Pingliang City,Baiyin City 5.0×1015molec/cm2 or more), and the third category is the Linxia Hui Autonomous Prefecture, Tianshui, Jiayuguan City, Dingxi City（4.5×1015molec/cm2 or more）, the fourth category is Jinchang City, Longnan City, Wuwei City（4.0×1015molec/cm2 or more）, the fifth class of Gannan Tibetan Autonomous Prefecture, Zhangye city, Jiuquan City（both 4.0×1015molec/cm2 or less）. To facilitate further research, from the above five categories in the selection of a typical representative（Lanzhou city, Qingyang city, Tianshui and Jiuquan city） concentration and the time and space distribution of the troposphere NO₂ column calculates the sine simulation model, model parameter display: From the sinusoidal model A value represents the concentration of NO₂ column from high to low troposphere is arranged as follows: Lanzhou City > Qingyang City> Tianshui City> Jinchang City> Jiuquan City, the overall highest concentration of Lanzhou City, reached 6.083×1015molec/cm2,Jiuquan City, lowest 3.59×1015molec/cm2; On behalf of the B value from the high to low order: Tianshui City> Qingyang City> Jiuquan City> Jinchang City> Lanzhou City, on the biggest growth for Tianshui City, reached 0.0035×1015molec/cm2, growth in the smallest of Lanzhou City, negative, indicates that Lanzhou City tropospheric column NO₂ concentration control has been a downward trend; From month growth trend B/A descending order of Tianshui City> Qingyang City> Jiuquan City>Jinchang City> Lanzhou City, the largest city of Tianshui, indicating that the concentration of tropospheric NO₂ column size and rapid growth; smallest for the Lanzhou City, is negative, indicating no increase in Lanzhou falling trend, Qingyang City, Jinchang City, Jiuquan City, on growth is positive, but the value is small,indicating that the column NO₂ concentration of the troposphere slow growth;Amplitude C order from big to small is Jinchang City> Jiuquan City> Lanzhou City>Qingyang City > Tianshui City, which the magnitude of the large change in Jiuquan City, variations of Tianshui city is the smallest, and latitude and temperature of reduce,tropospheric NO₂ column density variation amplitude decreases. From the point of view of cyclical changes, Lanzhou City high value appears in winter, low value in summer, reflecting the characteristics of "higher in winter and lower in", the rest is realized for "in summer and lower in" trend.（5）In this paper, we analyzed the influence of natural factors including terrain features, wind direction and wind speed, temperature and precipitation and other factors on the column concentration.And by using the population GDP, industrial GDP,civilian car ownership, energy consumption and other statistical data of Gansu Province from 2008 to 2015, through the correlation analysis between the concentration of NO₂ and the column, pointed out that the air quality of human factors in Gansu Province, the influence of coal consumption and industrial GDP on tropospheric NO₂ column concentration is obvious. Finally, according to the research of this paper, we put forward the related control measures.