Table 2.

Percentage changes of the average concentrations of air pollutants at Alert Level 1, 2 and 3 in relative to the pre-lockdown concentrations during COVID-19 lockdown in China.

Period	Area	PM2.5	PM10	SO2	CO	NO2	O3
Alert Level 1	NEC	−33.0%	−31.4%	−23.0%	−27.6%	−49.1%	47.8%
	NW	−28.7%	−1.8%	−5.7%	−20.5%	−44.0%	55.2%
	NCP	−34.5%	−32.0%	−28.2%	−31.7%	−53.2%	77.7%
	MG	−28.9%	−19.2%	−20.3%	−34.3%	−48.7%	52.8%
	TP	−23.8%	−8.7%	−9.4%	−15.6%	−41.2%	12.7%
	YR	−34.4%	−33.7%	−7.5%	−21.5%	−53.1%	62.0%
	CS	−17.7%	−21.3%	−17.4%	−23.3%	−53.2%	48.4%
	SC	−17.0%	−27.5%	−23.2%	−20.6%	−49.2%	11.9%
Alert Level 2	NEC	−59.0%	−47.3%	−46.9%	−47.4%	−54.6%	68.3%
	NW	−43.2%	21.5%	−31.9%	−52.3%	−50.0%	62.4%
	NCP	−58.3%	−37.2%	−42.2%	−51.1%	−38.6%	87.4%
	MG	−64.2%	−40.3%	−40.9%	−59.8%	−57.1%	69.0%
	TP	−32.2%	−3.3%	−19.5%	−29.1%	−36.9%	24.7%
	YR	−48.0%	−28.7%	3.1%	−24.8%	−25.5%	69.0%
	CS	−26.1%	−12.8%	−0.8%	−25.7%	−19.7%	63.1%
	SC	−16.0%	−14.9%	−11.1%	−15.0%	−19.0%	7.3%
Alert Level 3	NEC	−19.3%	−6.7%	−43.6%	−37.9%	−34.9%	86.2%
	NW	−36.3%	48.9%	−41.1%	−61.5%	−46.1%	79.2%
	NCP	−59.8%	−34.6%	−39.7%	−52.6%	−30.5%	115.5%
	MG	−63.3%	−29.6%	−48.1%	−63.6%	−50.3%	91.6%
	TP	−20.7%	21.7%	−24.1%	−33.8%	−26.2%	25.5%
	YR	−43.4%	−16.0%	20.9%	−31.6%	−3.4%	99.0%
	CS	−24.6%	−6.1%	13.4%	−29.1%	−6.1%	99.9%
	SC	−5.4%	−2.5%	5.2%	−13.0%	−3.1%	23.2%