Ozone seasonal evolution and photochemical production regime in the polluted troposphere in eastern China derived from high-resolution Fourier transform spectrometry (FTS) observations

Abstract. The seasonal evolution of O 3 and its photochemical production regime in a polluted region of eastern China between 2014 and 2017 has been investigated using observations. We used tropospheric ozone ( O 3 ), carbon monoxide (CO), and formaldehyde (HCHO, a marker of VOCs (volatile organic compounds)) partial columns derived from high-resolution Fourier transform spectrometry (FTS); tropospheric nitrogen dioxide ( NO 2 , a marker of NO x (nitrogen oxides)) partial column deduced from the Ozone Monitoring Instrument (OMI); surface meteorological data; and a back trajectory cluster analysis technique. A broad O 3 maximum during both spring and summer (MAM/JJA) is observed; the day-to-day variations in MAM/JJA are generally larger than those in autumn and winter (SON/DJF). Tropospheric O 3 columns in June are 1.55×10 18 molecules cm −2 (56 DU (Dobson units)), and in December they are 1.05×10 18 molecules cm −2 (39 DU). Tropospheric O 3 columns in June were ∼50 % higher than those in December. Compared with the SON/DJF season, the observed tropospheric O 3 levels in MAM/JJA are more influenced by the transport of air masses from densely populated and industrialized areas, and the high O 3 level and variability in MAM/JJA is determined by the photochemical O 3 production. The tropospheric-column HCHO∕NO 2 ratio is used as a proxy to investigate the photochemical O 3 production rate ( PO 3 ). The results show that the PO 3 is mainly nitrogen oxide ( NO x ) limited in MAM/JJA, while it is mainly VOC or mixed VOC– NO x limited in SON/DJF. Statistics show that NO x -limited, mixed VOC– NO x -limited, and VOC-limited PO 3 accounts for 60.1 %, 28.7 %, and 11 % of days, respectively. Considering most of PO 3 is NO x limited or mixed VOC– NO x limited, reductions in NO x would reduce O 3 pollution in eastern China.