中国大气环境治理的新启示--来自武汉疫情管控期间的自然实验

New implications of air pollution control in China:based on natural experiments during the COVID-19 lockdown in Wuhan

在武汉疫情管控期间,企业经济活动和机动车活动水平明显大幅下降,大部分污染源基本停止排放,意味着在此期间全国各地区应该出现优良天气,但是事实上在我国部分地区却出现了严重雾霾天气,这种反预期现象引起人们的普遍关注,甚至怀疑我国大气环境治理是否存在失误。根据这种反预期现象,提出环境污染应当是由流量污染和存量污染共同决定的猜想。为验证这一猜想,分别假设了两种情况:第一种只有流量污染,第二种既有流量污染又有存量污染,并用武汉疫情管控前后的实际排放数据模拟得到空气质量状况,寻找雾霾形成的规律,然后与武汉疫情管控前后实际监测数据进行对比,确定反预期现象的原因。实际数据和模拟数据对比发现,实际情况与假设1不符,与假设2相符。据此认为,大气污染是由当期排放的污染与积累的存量污染共同决定。在此基础上,进一步分析存量污染造成的经济损失,分析表明:2007年被低估1.64亿元,到2017年被低估3.83亿元;在消散率为0.05、贴现率为0.01时,流量、存量和流量与存量损失的差额分别为6.5亿元、50.5亿元和44.0亿元,这意味着2007—2017年总的经济损失被低估44.0亿元。在消散率为0.3、贴现率为0.1时,流量、存量和流量与存量损失的差额分别为4.6亿元、10.5亿元和5.9亿元,这意味着2007—2017年总的经济损失被低估5.9亿元。研究发现,长期累积形成的存量污染是一个被忽视的大气污染源,从而解释了在武汉疫情管控期间低水平经济活动条件下仍然会出现重度大气污染的经验事实。其政策含义在于,制定反污染政策需要根据存量污染的特征进一步完善相关政策设计。

During the lockdown imposed by the Chinese government when COVID-19 broke out in Wuhan,corporate production and motor vehicle activities decreased significantly.Most pollution sources basically stopped emitting pollution,suggesting that there should have been good air quality in all cities of China during this period,but severe haze still existed in some cities as a matter of fact.This counter-expectation phenomenon has attracted widespread attention;people wonder if misconduct existed in the process of air pollution control.Based on this understanding,this study put forward the conjecture that air pollution should be determined by both flow pollution and stock pollution.In order to verify this conjecture,this paper put forward two hypotheses:the first involved only flow pollution,and the second involved both flow pollution and stock pollution.Furthermore,the actual emission data before and after the COVID-19 lockdown in Wuhan were used to simulate the detection value of air quality,and then a comparison between the actual and simulated data was made to find out the cause of the counter-expectation phenomenon.The results showed that the actual situation was inconsistent with hypothesis 1,but was consistent with hypothesis 2.Based on this finding,this paper concluded that air pollution should be determined by both flow pollution and stock pollution.The economic loss caused by stock pollution was further analyzed.The result showed that the economic loss caused by stock pollution was underestimated by 0.164 billion yuan in 2007,and by 2017 it was underestimated by 0.383 billion yuan.When the dissipation rate was 0.05 and the discount rate was 0.01,the loss of flow pollution,that of stock pollution,and the difference between flow pollution and stock pollution were 0.65 billion yuan,5.05 billion yuan,and 4.40 billion yuan respectively,which meant that the total economic loss from 2007 to 2017 was underestimated by 4.40 billion yuan.When the dissipation rate was 0.3 and the discount rate was 0.1,the loss of flow pollution,that of stock pollution,the difference between flow pollution and stock pollution were 0.46 billion yuan,1.05 billion yuan and 0.59 billion yuan respectively,which meant that the total economic loss from 2007 to 2017 was underestimated by 0.59 billion yuan.This study has found that long-term accumulation of stock pollution is a neglected source of air pollution,which explains the empirical fact that severe air pollution still occured under low levels of economic activities during the COVID-19 lockdown in Wuhan.The policy implications of this study suggest that improvement of anti-pollution policies is needed according to the characteristics of stock pollution.