Impact Of Emission From Typical Energy Industry Base On Local Air Quality In Northwest China

Along with the implementation and operation of the national strategy for energy safety in the21st century and the Grand Western Development（GWD）programme since the 2000s,energy industries have gained rapid development in energy abundant northwest China which might deteriorate air quality and harsh ecological environment in this part of China.This PhD study examined the interactions between the changes in national energy development policies and the emission of NO_X and SO₂ from different areas as well as the shifting of energy industry from eastern China to western China in the past decade.This study focused on several“hot spots”in a large-scale national energy industrial base in northwest China,where SO₂ emissions have been significantly increasing in recent decades.To examine the effect of the GWD programme on air quality in northwest China,we selected two primary precursors,i.e.NO₂ and SO₂,which are the major emission pollutants in energy industries.Ozone Monitoring Instrument（OMI）retrieved columnar SO₂ and NO₂ from2005-2015 were used to assess the temporal-spatial distribution of these two precursor gases across northwest China.The two large-scale national energy bases,Midong-Wujiaqu Energy and Chemical Industrial Base and the Ningdong Energy and Chemical Industrial Base（NECIB）,where the OMI measured columnar SO₂ exhibited strongest incline from 2005 to 2016,were selected to assess the effect of the energy and chemical industry development on the air quality in local and surrounding regions by using satellite remote sensing technique,WRF-Chem modeling,and field sampling.The major findings from this PhD study are summarized below.（1）SO₂ has been increasing since 2005²015 in northwest China。Results show highest provincial SO₂ levels in Shanxi province,followed by Gansu,Xinjiang,Ningxia,and Qinghai.The long-term satellite derived data revealed that,in contrast to Beijing-Tianjin-Hebei（BTH）,Yangtze River Delta（YRD）,and Pearl River Delta（PRD）where widespread SO₂ decline was observed,columnar SO₂ in northwest China has been increasing,especially in Urumqi-Midong-Wujiaqu of Xinjiang,and Yinchuan and its surrounding area.Columar NO₂ shows a dramatical increase in BTH,YRD and PRD but a moderate increase in northwest China.（2）Development of MWIZ affects Urumqi city ambient air quality.The preliminary results from this PhD study revealed that mean columnar SO₂ in Midong-Wujiaqu Industrial Zone（MWIZ）was considerably higher than that in Urumqi city but there was a good association of the columnar SO₂ from 2005-2016 between MWIZ and Urumqi city at the correlation coefficient of R=0.504（p<0.005）.Measured daily air concentrations between these two region also showed significant correlation（R>0.586,p<0.005）.WRF-Chem simulations showed strong SO₂ atmospheric transport from MWIZ to Urumqi city in the wintertime subject to the prevailing winds,revealing a source-receptor relationship between the energy base and the city.The mean winds and composite anomalies of winds in several high PM_2.5 episodes occurring in Urumqi in the wintertime confirmed that the prevailing northly winds provided a main atmospheric pathway delivering air pollutants from MWIZ,located in the north of Urumqi City,to this capital city.The WRF-Chem predicted that SO₂ emissions from MWIZ contributed 38%of SO₂ concentration to Urumqi City in February 25 2016 during which a heavy PM_2.5 pollution episode occurred in the city.（3）Development of NECIB leads to high coincentrations of NMHCs.In the NECIB,where the one of the world largest coal liquefaction is located,two sampling sites were set up to investigate potential emissions of NMHCs.The one was located in an energy-chemical industrial base and the other in a coal chemical industrial base.Ambient air samples of VOCs were collected using SUMMA pre-evacuated 2-L electro-polished stainless steel canisters in NECIB from 22 to 31 December 2016,and NMHCs（57）were analyzed on a gas chromatography-mass selective detector/flame ionization detector（GC-MSD/FID）.The mean concentrations of NMHCs averaged over the sampling period were 39.31±18.77 ppbv in the energy chemical industrial base and 49.05±44.37 ppbv in the coal chemical industrial base,respectively.The composition of NMHCs at the two sampling sites were similar,with alkanes（accounting for 63%of total NMHCs level）>alkenes/acetylene（29%）>aromatics（8%）.Ethane,propane,acetylene,n-butane,and ethylene were the major components of NMHCs in NECIB,accounting for more 65%of the total NMHCs concentration.We detected high concentrations of alkanes and alkenes which were released mainly from industrial activities.The atmospheric levels of n-butane,normal pentane,ethylene,and propylene could be attributed to the volatilization of petroleum and its production.Source apportionment also suggested that acetylene was primarily emitted from coal combustion and most isobutane was generated from automobile exhaust.The order of the reactivities of NMHCs with OH is alkenes/acetylene>alkanes>aromatics.This suggests that alkenes/acetylene,mainly including propylene,ethylene,1-butylene,cis-2-butene,and isoprene,could be the primary contributor to O₃formation in the NECIB.Therefore,alkenes emission control is likely an effective measure for decreasing O₃ level in this region and its surroudings.Given continuous expansion and development of energy industry in these large-scale national energy industrial bases under the national strategy for the 21^st century energy safety,it is expected that air pollution in these emission“hot spots”would be further deteriorated which could otherwise affect local ecosensitve environment due to sparse vegetation coverage and precipitation.Further efforts should be made to study and mitigate environmental pollution associated with energy industry expansion and development,so as to improve ecological environment in northwest China.