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

The seasonal evolution of inline-formulaO₃ 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 (inline-formulaO₃), 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 (inline-formulaNO₂, a marker of inline-formulaNO_x (nitrogen oxides)) partial column deduced from the Ozone Monitoring Instrument (OMI); surface meteorological data; and a back trajectory cluster analysis technique. A broad inline-formulaO₃ 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 inline-formulaO₃ columns in June are inline-formula1.55×10¹⁸ molecules cminline-formula⁻² (56 DU (Dobson units)), and in December they are inline-formula1.05×10¹⁸ molecules cminline-formula⁻² (39 DU). Tropospheric inline-formulaO₃ columns in June were inline-formula∼50 % higher than those in December. Compared with the SON/DJF season, the observed tropospheric inline-formulaO₃ levels in MAM/JJA are more influenced by the transport of air masses from densely populated and industrialized areas, and the high inline-formulaO₃ level and variability in MAM/JJA is determined by the photochemical inline-formulaO₃ production. The tropospheric-column inline-formulaHCHO∕NO₂ ratio is used as a proxy to investigate the photochemical inline-formulaO₃ production rate (inline-formulaPO₃). The results show that the inline-formulaPO₃ is mainly nitrogen oxide (inline-formulaNO_x) limited in MAM/JJA, while it is mainly VOC or mixed VOC–inline-formulaNO_x limited in SON/DJF. Statistics show that inline-formulaNO_x-limited, mixed VOC–inline-formulaNO_x-limited, and VOC-limited inline-formulaPO₃ accounts for 60.1 %, 28.7 %, and 11 % of days, respectively. Considering most of inline-formulaPO₃ is inline-formulaNO_x limited or mixed VOC–inline-formulaNO_x limited, reductions in inline-formulaNO_x would reduce inline-formulaO₃ pollution in eastern China.