AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Boundary Layer Characteristics and PM2.5 Concentration Diurnal Variation on Cloudless Days in Beijing Based on UHF Wind-profiler and Related Meteorological and Air Quality Observations
YUFANG TIAN, Daren Lyu, Institute of Atmospheric Physics,Chinese Academy of Sciences
Abstract Number: 860 Working Group: Remote and Regional Atmospheric Aerosol
Abstract Based on boundary layer wind-profiler observations, this study revealed important characteristics of the diurnal variation of atmospheric refractive index structure parameter (Cn2) on cloudless days in Beijing. By investigating the vertical distribution of Cn2 on a total of 114 completely cloudless days over a two-year period (March 2011 to March 2013), three patterns of Cn2 diurnal variation were found. Pattern 1 showed weak diurnal variation, happening in winter months and with low humidity. Pattern 3 showed obvious diurnal variation, with larger Cn2 at nighttime and smaller values during daytime, detected in high humidity months. In the transition months, with transitional characteristics between patterns 1 and 3, there was Pattern 2. Patterns 1, 2 and 3 accounted for 40.3%, 12.3% and 47.4% of cloudless days, respectively. Variations in characteristics between the three patterns were found to be related to the variation in dominant air flow, terrain effects, and echoing mechanisms. Higher humidity and echoes scattering from anisotropic structures in the refractive index resulted in higher Cn2.
Since this study covered the characteristics of the whole boundary layer, which provided information on a variety of boundary layer processes, the closely related air pollutant properties in each pattern were also investigated.
PM2.5 concentrations were highest in Pattern 1 and lowest in Pattern 3. The concentrations of PM2.5 demonstrated diurnal variation for each pattern, with larger values at nighttime, corresponding to the higher humidity at nighttime than during daytime. However, the differences in PM2.5 concentrations between nighttime and daytime were largest in Pattern 1 and smallest in Pattern 3. These characteristics were the combined result of the lower atmospheric wind speed, the Cn2-indicated turbulence intensities in the daytime and the function of higher humidity at nighttime, the inversion layer occurrence rate, and vertical motions.