[Characteristics of Primary Pollutants of Air Quality in Cities Along the Taihang Mountains in Beijing-Tianjin-Hebei Region During 2014-2016].

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 PM, O-8h, NO and PM from most to least important in Beijing, and PM, PM, O-8h, NO, SO and CO in the other four cities. Three-year average percentages of days with PM as the primary pollutant in each city were similar (53.3%-58.1%), however, percentages of days with PM as primary pollutant increased, while percentages of O-8h decreased basically, from north to south. Except for Handan with a significant descending trend, percentages of days with PM as primary pollutant varied slightly in the other four cities during the study period, and percentages of O-8h of Shijiazhuang, Xingtai and Handan increased significantly in 2016. Percentages of NO slightly declined year by year in Beijing, and the other four cities mainly showed the opposite trend. Monthly variation curves of days with PM and O-8h as primary pollutants showed "W" and "inverted U" types respectively, while the high value interval of days with PM as primary pollutant occurred between March and May. With the exception of Beijing, peak of monthly variation curves for days with NO 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 PM and/or PM as primary pollutants increased level by level, with percentages of PM trending downwards and PM upwards. Meanwhile, days with O-8h as the primary pollutant mostly appeared in the range between "moderate" and "unhealthy" levels, and NO was only prominent in "moderate" level.