Measurement report: Ice nucleating abilities of biomass burning, African dust, and sea spray aerosol particles over the Yucatan Peninsula

Abstract. Most precipitation from deep clouds over the continents and in the intertropical convergence zone is strongly influenced by the presence of ice crystals, whose formation requires the presence of ice nucleating particles (INP). Although there are a large number of INP sources, the ice nucleating abilities of aerosol particles emitted from oceans, deserts, and wildfires are poorly described at tropical latitudes. To fill this gap in knowledge, the UNAM-MicroOrifice Uniform Deposit Impactor-Droplet Freezing Technique (UNAM-MOUDI-DFT) was built. Aerosol samples were collected in Sisal and Merida, Yucatan (Mexico) under the influence of cold fronts, biomass burning (BB), and African dust (AD), during five short-term field campaigns between January 2017 and July 2018.

The three different aerosol types were distinguished by characterizing their physicochemical properties. Marine aerosol (MA), BB, and AD air masses were found to contain INP; the highest concentrations were found for AD (from 0.071 L⁻¹ to 36.07 L⁻¹), followed by MA (from 0.068 L⁻¹ to 18.90 L⁻¹), and BB (from 0.063 L⁻¹ to 10.21 L⁻¹). However, MA had the highest surface active site density (ns) between −15 °C and −30 °C. Additionally, supermicron particles contributed more than 72 % of the total INP concentration independent of aerosol type; MA had the largest contribution from supermicron particles.