资源环境科技发展态势分析平台

We conducted the first real-time continuous vertical measurements of particle extinction (b(ext)), gaseous NO2, and black carbon (BC) from ground level to 260m during two severe winter haze episodes at an urban site in Beijing, China. Our results illustrated four distinct types of vertical profiles: (1) uniform vertical distributions (37% of the time) with vertical differences less than 5 %, (2) higher values at lower altitudes (29 %), (3) higher values at higher altitudes (16 %), and (4) significant decreases at the heights of similar to 100-150m (14 %). Further analysis demonstrated that vertical convection as indicated by mixing layer height, temperature inversion, and local emissions are three major factors affecting the changes in vertical profiles. Particularly, the formation of type 4 was strongly associated with the stratified layer that was formed due to the interactions of different air masses and temperature inversions. Aerosol composition was substantially different below and above the transition heights with similar to 20-30% higher contributions of local sources (e. g., biomass burning and cooking) at lower altitudes. A more detailed evolution of vertical profiles and their relationship with the changes in source emissions, mixing layer height, and aerosol chemistry was illustrated by a case study. BC showed overall similar vertical profiles as those of b(ext) (R-2 = 0.92 and 0.69 in November and January, respectively). While NO2 was correlated with b(ext) for most of the time, the vertical profiles of b(ext) / NO2 varied differently for different profiles, indicating the impact of chemical transformation on verti-cal profiles. Our results also showed that more comprehensive vertical measurements (e.g., more aerosol and gaseous species) at higher altitudes in the megacities are needed for a better understanding of the formation mechanisms and evolution of severe haze episodes in China.