Primary pollutants of air quality in Beijing, Baoding, Shijiazhuang, Xingtai, and Handan cities along the Taihang Mountains were analyzed to investigate their spatial distribution characteristics and temporal variation trends during 2014-2016. The results showed that the primary pollutants were ranked as PM2.5, O3-8h, NO2 and PM10 from most to least important in Beijing, and PM2.5, PM10, O3-8h, NO2, SO2 and CO in the other four cities. Three-year average percentages of days with PM2.5 as the primary pollutant in each city were similar (53.3%-58.1%), however, percentages of days with PM10 as primary pollutant increased, while percentages of O3-8h decreased basically, from north to south. Except for Handan with a significant descending trend, percentages of days with PM2.5 as primary pollutant varied slightly in the other four cities during the study period, and percentages of O3-8h of Shijiazhuang, Xingtai and Handan increased significantly in 2016. Percentages of NO2 slightly declined year by year in Beijing, and the other four cities mainly showed the opposite trend. Monthly variation curves of days with PM2.5 and O3-8h as primary pollutants showed "W" and "inverted U" types respectively, while the high value interval of days with PM10 as primary pollutant occurred between March and May. With the exception of Beijing, peak of monthly variation curves for days with NO2 as the primary pollutant was occurred in October in the other four cities. From "moderate" to "hazardous" levels for air quality, the percentages of days with PM2.5 and/or PM10 as primary pollutants increased level by level, with percentages of PM10 trending downwards and PM2.5 upwards. Meanwhile, days with O3-8h as the primary pollutant mostly appeared in the range between "moderate" and "unhealthy" levels, and NO2 was only prominent in "moderate" level.
Keywords: Beijing-Tianjin-Hebei Region; air quality; cities along Taihang Mountains; primary pollutants; variation characteristics.