Analysis of Houston Aerosols as Ice Nucleating Particles During TRACER

Changes in ice nucleating particles (INPs) have an uncertain impact on the formation, lifetime, and precipitation of deep convective clouds. As part of the TRacking Aerosol and Convection interaction ExpeRiment (TRACER) campaign, the team at Texas A&M University deployed three Davis Rotating Uniform size-cut Monitors (DRUMs) throughout Houston to analyze INPs in the region. Two of the instruments were located at fixed sites (Department of Energy’s main site in La Porte, Texas and the ancillary site in Guy, Texas), which sampled continuously for the duration of TRACER’s intensive operational period (June-September 2022). The third DRUM was housed within the Texas A&M Rapid Onsite Atmospheric Measurement Van (ROAM-V) mobile instrument platform, which deployed on select days to coastal and inland sites. The DRUMs collect ambient aerosol in four size bins: >3, 3-1.2, 1.2-0.34, and 0.34-0.15 μm. After the campaign, aerosol samples from each DRUM were analyzed at Texas A&M University using a custom 16-droplet array ice nucleation apparatus. Ice nucleation experiments for each instrument’s 3^rd size bin (1.2-0.34 μm) reveals a similarly broad range of nucleation temperatures, from -31 to -14 °C, throughout the campaign. Each site is dominated by weakly to moderately effective INPs (most frequent nucleation temperature: ~ -25 °C). However, multiple less-frequent modes of effective (-20 to -10 °C) INPs are also present at each site, indicating diverse aerosol populations. Initial analysis of the other DRUM stages suggests the frequency of effective ice nucleation increases with particle diameter. The characterization of the ice nucleating ability for Houston’s aerosols can be used to help constrain local/regional convection-permitting models.