Abbreviations	Full name
BTH	Beijing-Tianjin-Hebei
CMA	China meteorological administration
COC	centre of China
DU	Dobson units
MLS	microwave limb sounder
MSL	mid-southern Liaoning
MYC	mean year-on-year changes
NOx	nitrogen oxides
OCC	ozone column concentration
OCCLT	OCC in the lower troposphere
OMI	ozone monitoring instrument
PBLH	planetary boundary layer height
PRD	Pearl river delta
QTP	Qinghai--Tibet plateau
SCB	Sichuan basin
TOC	total organic carbon
UCS	Urumqi-Changji--Shihezi
VOCs	volatile organic compounds
YRD	Yangtze river delta