中國城市嚴重的空氣污染與企業及家庭對燃煤的依賴密切相關。因此,以天然氣等清潔能源替代燃煤被視為治理空氣污染的重要手段。在能源替代政策的推進下,"煤改氣"工程正在眾多大城市如火如荼地進行。在此背景下,本文針對清潔能源替代問題進行經濟學討論,并對城市"煤改氣"政策施行效果進行實證檢驗。本文首先利用包括西氣東輸等天然氣長輸管道項目作為外生沖擊,考察了城市天然氣供應對空氣污染的影響。利用城市面板數據回歸的結果發現,長輸管道的聯通對城市空氣污染有顯著地遏制作用,而這種作用在煤炭城市更為明顯。在穩健性檢驗部分,利用城市液化石油氣代替天然氣進行安慰劑檢驗,發現天然氣長輸管道對于液化石油氣的供給并沒有顯著促進作用,后者也未影響天然氣替代煤炭對城市空氣污染的減排效應。其次,在考察城市特征對天然氣長輸管道聯通影響的基礎上,考察途經城市是否存在選擇效應,結果發現空氣污染、煤炭消費等變量對管道聯通均無顯著影響,表明城市天然氣管道聯通并不存在明顯的選擇效應。在機制分析部分,進一步分析城市天然氣管道長度、供應量與使用人口對空氣污染的影響,發現天然氣主要通過替代城市民用燃煤來遏制空氣污染,對工業燃煤造成的污染則減排作用不明顯。最后,從價格角度討論了天然氣難以通過替代工業燃煤遏制空氣污染的可能原因,并分析了"煤改氣"政策在現階段的局限性。

Serious air pollution in China’s urban areas is closely related to firm’s and household’s coal consumption. Therefore,the replacement fire coal with natural gas and other types of clean energy is deemed to be the crucial means to control air pollution.Promoted by the energy substitution policy,the ‘coal to gas’ engineering is taking place like a raging fire in numerous big cities.Under this background,this paper carries out economic discussion about the issue of energy substitution policy and conducts empirical tests on the effect of the execution of the ‘coal to gas’ policy. The paper firstly uses the west-east natural gas long-distance pipeline project as exogenous shocks to investigate the effect of natural gas consumption on urban air pollution. Estimating with urban panel data,we find that city’s pipeline connection significantly reduces air pollution and it is more prominent in coal cities. As for the robustness test on the research result,this paper firstly carries out a placebo test through the substitution of the liquefied petroleum gas for natural gas. According to the test results,natural gas long-distance pipeline can’t significantly promote the supply of the liquefied petroleum gas. In addition,the latter doesn’t influence the reduction effect of the substitution of natural gas for fire coal on the city air pollution. Secondly,this paper also inspects the influence of the urban characteristics on the connection of natural gas long-distance pipeline to study whether the cities on the way of transportation can exert selection effect. The results show that the air pollution,coal consumption and other variables don’t have significant influence on the connection of the pipeline. Consequently,the connection of the natural gas pipeline won’t exert a significant selection effect. As for the mechanism analysis,this paper further analyzes the effect of city’s natural gas pipe lengthen,gas supply,and accessed population. By virtue of the data on the per capital industrial and civilian coal consumption as well as the data on various industrial and civilian air pollutants,we find that natural gas mainly substitutes urban civil coal consumption rather than industrial coal consumption to improve air quality. Finally,we discuss this difference from the aspect of natural gas pricing and analyze the limitation of ‘coal to gas’ policy at current stage.