Nonlinear Response Relationship Between Ozone and Precursor Emissions in the Pearl River Delta Region Under Different Transmission Channels

Abstract

With the rapid development of urbanization, ozone (O3) pollution is an ongoing occurrence in the Pearl River Delta (PRD) region in China. The effective control of O3 pollution is a great challenge owing to the nonlinear relationship between O3 and precursor emissions and the effect of meteorological conditions. Based on the regional air quality model CAMx-OSAT (ozone source apportionment technology), O3 formation regimes were determined, and inter-city transportation across PRD was quantified under different transmission channels. The results showed that spatial differences were observed for the O3 formation regimes under different transmission channels. The VOCs-sensitive regime was mainly located in the central areas of the PRD region, and the NOx-sensitive regime was distributed in the suburban areas of the PRD regions under calm wind conditions. When the northeast wind was prevailing, the polluted air mass of the urban agglomeration was transmitted southwesterly downward, resulting in the downwind areas being transformed to VOCs-sensitive; the upwind areas were still NOx-sensitive. Under the southeast wind, the VOCs-sensitive regime had a banding distribution along the southeast-northwest direction, and the remaining areas were NOx-sensitive. With the influence of transmission channels, downwind cities were significantly affected by the transmission of upwind urban agglomerations (41%-87%), whereas the local formation was the main contributor under the calm wind conditions (60%-87%). To explore the relationship between O3 and precursor emissions, a series of sensitivity tests were designed. The results showed that maximized areas (20%-36%) with reductions in O3 can be achieved by reducing VOCs and NOx in the corresponding sensitive regimes, and the maximized level with the reduction in O3 can be fulfilled by reducing VOCs in the VOCs-sensitive regime. For the typical city Jiangmen, the area that met the standard increased the most under the calm wind (11%) and southeast wind (8%) conditions when VOCs and NOx were reduced in the corresponding sensitive regimes. Additionally, under northeast wind conditions, reducing VOCs in the VOCs-sensitive regime can more effectively control O3, as the area up to the standard increased by 140%.