Characteristics of Meteorological Elements and Pollutant Concentration in the Boundary Layer of Radiation Fog on Jiangsu Coast Based on Unmanned Aerial Vehicles

To further investigate the vertical distribution characteristics of meteorological elements and pollutant concentrations in the boundary layer during radiation fog, a comprehensive observation experiment was conducted in Donghai County, Jiangsu province using unmanned aerial vehicles (UAVs) in the winter of 2020. The findings revealed that the thickness of the inversion layer on foggy days is tens to hundreds of meters thicker than on sunny days, with a strength increase of 0.5–1°C (100 m)⁻¹. On foggy days, wind shear occurs at low altitudes, while the wind shows minimal vertical variation. By contrast, on sunny days, wind speed remains relatively stable at low altitudes; however, the wind direction rotates clockwise with height. Radiation fog with a deep single-layer inversion structure exhibits greater intensity compared to fog with a double-layer inversion structure. During the same radiation fog event, fog intensity remains unaffected by changes in wind direction, while lower wind speeds are more conducive to the formation of dense fog. From the perspective of pollutant vertical distribution, total volatile organic compound (TVOC) concentrations at the same height within the inversion layer are higher on sunny days than on foggy days. Before and during the generation stage of radiation fog, the rate of SO₂ concentration decreases with height and is significantly higher than that during the same period on sunny days. The vertical variations in O₃ and NO₂ on clear and foggy days are strongly negatively correlated, with the O₃ gradient near the ground on foggy days being much steeper than on clear days. Concentrations of PM_1.0, PM_2.5, and PM₁₀ are more than twice as high on foggy days compared to sunny days, while CO remains relatively stable with minimal vertical variation during radiation fog. TVOC, NO₂, PM_1.0, PM_2.5, and PM₁₀ are affected by the strong inversion layer during radiation fog, leading to their accumulation within the inversion layer. After the fog dissipates, the cumulative change rate of these pollutants decreases significantly compared to pre-fog conditions. The reduction in cumulative change rate is more pronounced for particulate pollutants than for gases, with larger particles showing a greater decrease than smaller ones. At night, NO and other reducing substances emitted from the ground struggle to move upward, resulting in much lower O₃ consumption in the upper layer compared to the lower layer. Consequently, O₃ concentrations in the upper layer are significantly higher than those in the lower layer at night. During the day, enhanced solar radiation and the development of an unstable boundary layer promote the downward mixing of O₃ from the upper atmosphere, leading to an increase in O₃ levels and PM_2.5 emissions; this results in a more consistent vertical variation of O₃ and PM_2.5 during the daytime.