The Influence of the Saharan Dust on Air Quality and Mixed-Phase Cloud Formation in the Yucatan Peninsula

Several studies have suggested that the Yucatan Peninsula is influenced by mineral dust from the Sahara Desert, especially in July associated with the strengthening of the Caribbean low level jet. The arrival of African mineral dust to Mexican territory can result in: i) a modification of the soil composition, ii) an increase in particulate matter (PM) levels, iii) an increase in the concentration and variability of microorganisms (including opportunistic pathogens), and iv) an alteration of the local precipitation patterns given that mineral dust particles can catalyze ice cloud formation.

Three short-term field campaigns were conducted to confirm the arrival of African dust into the Yucatan Peninsula, one in Sisal (21.16°N, 90.04°W) and two in Merida (20.98°N, 89.64°W) in July 2017 and July 2018. Aerosol particles were monitored with optical particle counters (e.g., a LasAir for particle size distribution, and a condensation particle counter, CPC, for total particle concentration), in addition to PM_2.5 and PM₁₀ monitors. Aerosol chemical composition was obtained by two different techniques, X-ray fluorescence (XRF) and Ion-exchange Chromatography (IC), from aerosol particles collected with Partisol and MiniVol samplers. The concentration and composition of culturable microorganisms (i.e., bacteria and fungi) were also determined. Finally, the concentration of ice-nucleating particles (INPs) was obtained with the UNAM – Micro orifice uniform deposit impactor – Droplet freezing technique (UNAM-MOUDI-DFT). The experimentally obtained results were complemented by satellite data, and HYSPLIT back-trajectories.

Combining the off-line and on-line sensors, the arrival of mineral dust particles from the Saharan desert into the Yucatan Peninsula was confirmed for two consecutive years. High concentration of mineral dust tracers (e.g., Fe, Al, K, and Si) were found upon the arrival of the African plumes. Furthermore, the PM_2.5, PM₁₀, total aerosol particle concentration, and microorganism’s concentration were found to be higher upon the arrival of the Saharan dust, with a more pronounced increase in 2018. The African plumes contained a variety of microorganisms those of which were identified, while very efficient INPs were found to be brought into the Yucatan Peninsula during the arrival of Saharan dust air masses.