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-formulaNOx (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-formulaNOx) limited in MAM/JJA, while it is mainly VOC or mixed VOC–inline-formulaNOx limited in SON/DJF. Statistics show that inline-formulaNOx-limited, mixed VOC–inline-formulaNOx-limited, and VOC-limited inline-formulaPO3 accounts for 60.1 %, 28.7 %, and 11 % of days, respectively. Considering most of inline-formulaPO3 is inline-formulaNOx limited or mixed VOC–inline-formulaNOx limited, reductions in inline-formulaNOx would reduce inline-formulaO3 pollution in eastern China.
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