Increase of ozone concentrations, its temperature sensitivity and the precursor factor in South China

Abstract

A B S T R A C TConcerns have been raised about the possible connections between the local and regional photochemical problem and global warming. The current study assesses the trend of ozone in Hong Kong and the Pearl River Delta (PRD) in South China and investigates the interannual changes of sensitivity of ozone to air temperature, as well as the trends in regional precursors. Results reveal, at the three monitoring sites from the mid-1990s to 2010, an increase in the mean ozone concentrations from 1.0 to 1.6 mg m (3 per year. The increase occurred in all seasons, with the highest rate in autumn. This is consistent with trends and temperature anomalies in the region. The increase in the sensitivity of ozone to temperature is clearly evident from the correlation between ozone (OMI [Ozone Monitoring Instrument] column amount) and surface air temperature (from the Atmospheric Infrared Sounder) displayed in the correlation maps for the PRD during the prominently high ozone period of JulyÁ September. It is observed to have increased from 2005 to 2010, the latter being the hottest year on record globally. To verify this temporal change in sensitivity, the ground-level trends of correlation coefficients/regression slopes are analysed. As expected, results reveal a statistically significant upward trend over a 14-year period (1997Á2010). While the correlation revealed in the correlation maps is in agreement with the corresponding OMI ozone maps when juxtaposed, temperature sensitivity of surface ozone also shows an association with ozone concentration, with R 00.5. These characteristics of ozone sensitivity are believed to have adverse implications for the region. As shown by ground measurements and/or satellite analyses, the decrease in nitrogen oxides (NO 2 ) and NO x in Hong Kong is not statistically significant while NO 2 of the PRD has only very slightly changed. However, carbon dioxide has remarkably declined in the whole region. While these observations concerning precursors do not seem to adequately support an increasing ozone trend, measured surface levels of formaldehyde, a proxy for volatile organic compound (VOC) emissions, have risen significantly in the PRD (2004Á2010). Hence, the reactive VOCs in the PRD are likely to be the main culprit for the increase of ozone, as far as precursors are concerned. Despite the prevailing problem, model simulations suggest prospects for improvement in the future.

Observed trends in ground-level O<sub>3</sub> in Monterrey, Mexico, during 1993–2014: comparison with Mexico City and Guadalajara

“…The recurrent downward spikes in the O 3 annual cycles within the MMA between July and August result from high wind speeds (> 10 km h −1 on average) that disperse O 3 precursors and increase the boundary layer height (ProAire-MMA, 2008). The peak in O 3 observed in September is characteristic of humid regions and can be ascribed to an increase in OH radicals derived from the increment in RH during the rainy season (Lee et al, 2014). A marked increase in RH within the MMA during September is consistent with the increase in O 3 observed as reported by Lee et al (2014).…”

“…The peak in O 3 observed in September is characteristic of humid regions and can be ascribed to an increase in OH radicals derived from the increment in RH during the rainy season (Lee et al, 2014). A marked increase in RH within the MMA during September is consistent with the increase in O 3 observed as reported by Lee et al (2014). Over the Midwestern and (Zheng et al, 2007).…”

Springtime warming and biomass burning causing ozone episodes in South and Southwest China

“…We use the statistical correlation of ozone (ozone total column) with surface temperature to show the spread of ozone across China. This correlation denotes the sensitivity of ozone to temperature which has previously revealed ozone blackspots of the PRD and the Sichuan basin in Southwest China (Lee et al 2014). The inter-comparison between satellite ozone data and surface ozone data (S4a) lends support to this method which conveniently tracks the temporal and spatial changes of ozone distribution.…”

Long-term O<sub>3</sub>–precursor relationships in Hong Kong: field observation and model simulation

“…Further investigation found that temperature and solar radiation in summer increased (p < 0.05) in these years (see Fig. S11), whereas they had no significant change in other seasons (the reasons remain unclear), consistent with the fact that an increase in temperature and solar radiation would enhance the photochemical reaction rates, resulting in O 3 increase in summer (Lee et al, 2014). On the other hand, the unchanged winter O 3 trend was in line with the unchanged NO x and TVOC values in winters of the past 10 years.…”