From Wave Crest to Wind Drift: Ocean-Atmosphere Microplastics in Three Mexican Coastal Zones

SALVADOR REYNOSO-CRUCES, Harry Alvarez-Ospina, Luis A. Ladino, Roberto Rosal, Carlos Edo, Universidad Nacional Autónoma de México

     Abstract Number: 380
     Working Group: Aerosol Processes and Properties in Changing Environments in the Anthropocene

Abstract
Global plastic production reached 400 Mt in 2022 and could exceed 1 Gt yr⁻¹ by 2050, intensifying concern about microplastics (MPs; 1 µm–5 mm). We quantified MPs at the ocean–atmosphere interface of three Mexican coastal sites, i.e., Veracruz (Gulf of Mexico), Manzanillo (Mexican Pacific), and Cozumel (Caribbean Sea), to assess the concentrations, polymer composition, and cross-boundary transfer of MPs. Morning and afternoon aerosols were collected with a high-flow impinger, and seawater profiles (0–10 m) were obtained with a horizontal Van Dorn bottle. MPs were isolated, digested, visually presorted, and confirmed by micro-FTIR. Strict quality-assurance protocols minimized contamination, and size-corrected abundances were derived from random FTIR subsamples.

Nine polymers were identified in 108 airborne and 72 water samples. Polyester dominated (46 %), followed by acrylics and polyethylene. Mean airborne concentrations were 3.9, 3.2, and 2.8 MPs m⁻³ in Veracruz, Manzanillo and Cozumel, respectively, and declined 45 % during afternoon offshore breezes. Seawater contained 17 MPs m⁻³ at the ocean surface; however, only 4 MPs m⁻³ were observed at 9 m depth. Although fibers represented 70 % of airborne MPs, this fraction was lower (60 %) in seawater, indicating preferential aerosolization of these buoyant and elongated particles. Orthogonal partial least squares discriminant analysis (OPLS-DA) revealed overlapping spectral fingerprints between airborne and surface water samples, and statistical coupling with wind vectors showed aerosolization within three hours of sea-spray generation. Artificial non-plastic dyed cellulose particles were 1.4-fold more abundant than MPs in aerosols, underscoring the need for chemical verification.

Our results show that ports are focal points for MPs exchange, modulated by diurnal breezes and polymer buoyancy. These baseline data constrain emerging emission models and highlight the need to integrate atmospheric pathways into Mexican plastic-waste strategies.