Effects of boundary layer dynamics and meteorology on ultrafine particle formation and growth

Abstract

It is currently not well understood how the planetary boundary layer (PBL) dynamics affects the formation and growth of ultrafine particles in the atmosphere, because of the limited co-located aerosol size distributions and lidar measurements. Here we show, from long-term in-situ observations, a clear link between boundary layer processes and surface aerosol dynamics. Aerosol size distributions in the diameter range from 7 to 300 nm were measured with a scanning mobility particle sizer (SMPS) at the University of Alabama Huntsville campus in 2016, 2017, and 2022. The backscatter of larger aerosols was measured using a co-located lidar ceilometer. Meteorological surface parameters including temperature, relative humidity, station pressure, wind speed and direction, solar radiation, and precipitation were also measured. New particle formation (NPF) and long growth (over 12 h) events occurred most frequently during the winter, unlike many other locations where NPF events occur more frequently in spring and fall, indicating that cooler temperatures play important roles in ultrafine particle formation in the warm subtropical environment. During the summer with strong solar radiation, there were more short-time growth events (less than 6 h), likely associated with convection within the boundary layer. Our observations also show cold fronts affect the measured aerosol size distributions because the combination of precipitation scavenging and cleaner air can provide thermodynamic conditions favorable for NPF and aerosol growth. These results highlight the importance of meteorology on aerosol formation and growth.