Tower observed vertical distribution of PM2.5, O3 and NOx in the Pearl River Delta

The vertical structure characteristics of the concentrations of PM2.5, O-3 and NOx are analyzed in conjunction with the meteorological data collected in December 2017 from a new meteorology tower in the Pearl River Delta region. The results show that: (1) The concentration of PM2.5 generally decreased with height, while the magnitude of the decrease differed between the polluted and the clean situations. The concentration of O-3 increased with height, and it increased more drastically during the polluted days than during the clean days. The vertical distribution of NOx concentration was quite similar to that of PM2.5, while the gradient of NOx concentration was much steeper below 220 m and was more gentle over 220 m. (2) The diurnal cycles of PM2.5 were different at different heights, while the diurnal cycles of O-3 and NO. were similar at all heights. A diurnal pattern with a single peak appearing during 14:00 to 16:00 Local Standard Time was observed for PM2.5 at higher altitudes (220 m and 335 m), hinting that the secondary formation contributed significantly to PM2.5 at higher layers. (3) The correlation coefficients between PM2.5 and O-3 were weak near the ground but increased with height and maintained their positive values. O-3 and NOx were generally negatively correlated, and the correlation coefficients between the two pollutants decreased with height. The correlation between PM2.5 and NOx was always significant at all heights of the observation.