Spatiotemporal variability of surface extinction coefficient based on two-year hourly visibility data in mainland China

Abstract Visibility is an important indicator for weather and air quality. Historical subjective visibility observations suffer from large uncertainty. Based on hourly instrumental visibility data at 2356 meteorological stations during 2016–2017 in mainland China, this study presents a closer look at the spatiotemporal variability of visibility-derived surface extinction coefficient (σe). The data reveal that the regional haze is concentrated over North China Plain, the Sichuan Basin and Central China. Seasonal variations of σe in different regions are similar, although their seasonal variation amplitudes show subtle spatial dependence. σe generally decreases from January to April or May, then remains relatively lower values until August and finally starts to increase gradually until December. The largest seasonal variation is found in Xinjiang Autonomous region where the regional mean σe ranges from 0.55 km−1 in January (maxima) to 0.12 km−1 in June (minima). Winter haze is often found at urban agglomerations in Northeast China. Pronounced diurnal variation of σe is evident, especially in winter and in northern China. Peak values are generally observed between 7:00 and 9:00 a.m. and they appear later in winter relative to summer. Lower values are generally found between 13:00 and 15:00 p.m. A large-spread of regional aerosol pollution with rapid evolution in North China Plain is well captured by the visibility network. Automatic visibility network is a great supplement for air quality monitoring network. Much attention should be paid to its great potential in air quality study.