Planetary Boundary Layer Effect on Vertical Transport of Black Carbon Concentration Under Different Meteorological Conditions
Abstract
: Unlike other pollutants, aerosols, especially the absorbing aerosols, consisting mainly of "black carbon" (BC), interact strongly with the planetary boundary layer (PBL). This study determines the impact of the evolution of PBL and long-range transport on equivalent BC (eBC) concertation under different metrological conditions such as clear sky, foggy (visibility <= 1km), and hazy day (visibility <= 5 km during the non-fog day), high relative humidity and temperature; also, diurnal and seasonal variability was evaluated. The mean eBC concentration was found to be the lowest during summer, followed by autumn and spring, and the highest in winter for the year 2020. In contrast, the average PBL height was the lowest in autumn, followed by summer and winter, and the highest in spring. The resulting behavior was due to the higher number of rainy days during the summer. The eBC concentration at ground level showed several peaks throughout the day. The peaks during mornings and evenings were likely due to local sources and the PBL diurnal evolution. Elevated eBC concentrations during noon and late-night have also been observed, driven by the transport of aerosols from distant sources. The long-range transport of aerosols was confirmed by air mass back trajectories analysis using the HYSPLIT model. The eBC concentration was higher below the PBL than above the PBL. Several case studies were also studied to find the impact of different meteorological conditions. The development of PBL was suppressed by fog and haze, further weakening the vertical mixing of aerosols, leading to higher eBC concentration at the ground. High RH
(ALMOST EQUAL TO 100%) with high temperature (28 °C) yields the highest PBL height and higher eBC concentration at 4m compared to 230 m.