Hygroscopicity of Microplastic and Mixed Microplastic Aqueous Ammonium Sulfate Systems

Abstract

A growing body of research suggests the presence and long-range transport of microplastics in the atmosphere. However, the interactions between these microplastics and atmospheric aerosol are poorly understood. Environmental microplastics vary in color, morphology, and chemical composition and become oxidized over time by UV, mechanical, and biological action. Once introduced to the atmosphere, these microplastics will likely become mixed with atmospheric aerosol. Determining how microplastics interact with aerosol particles and how they may alter aerosol physical properties, including water uptake and loss, is necessary to understand the impact of these microplastics on our environment. Herein, we investigate the effect of microplastics on the water activity of bulk water and ammonium sulfate solutions. We compare a variety of plastic compositions and microplastic morphologies including plastics that have been aged by UV irradiation and mechanical forces in the lab. In addition, we investigate the water uptake and loss in microplastic samples through dynamic vapor sorption. We find an increase in total water sorption for UV-aged plastics compared to pristine plastics. Finally, we investigate the effect of fractional surface coverage on the equilibration time scale.

Efficient Atmospheric Transport of Microplastics over Asia and Adjacent Oceans

“…MPs may become slightly hydrophilic after prolonged UV-aging. 48 However, our simulations showed that wet scavenging contributed <2% of the total atmospheric removal of MPs and thus had only minor effects on the atmospheric transportability of MPs. The spatial pattern of MPs’ wet deposition was similar to that of precipitation, with strong monsoonal variations ( Figure S2 ).…”

“…We assumed MPs to be hydrophobic and that wet scavenging of MPs involved only the washout by precipitation (Text S1). MPs may become slightly hydrophilic after prolonged UV-aging . However, our simulations showed that wet scavenging contributed <2% of the total atmospheric removal of MPs and thus had only minor effects on the atmospheric transportability of MPs.…”

Buoyancy and Brownian motion of plastics in aqueous media: predictions and implications for density separation and aerosol internal mixing state

“…Characterizing solid inclusions in aerosol droplets without influencing them proves difficult 35,36 and new techniques are needed meet this challenge. A better understanding of the mixing state of plastic inclusions in ambient aerosol is necessary to predict how these plastics will alter our current understanding of aerosol properties such as diffusion of water in and out of the droplets, 7 chemistry occurring on the surface of the plastic or due to the leaching of chemical species from the plastic into the aqueous phase, [56][57][58] and their ability to act as ice nuclei. 59…”

“…3–6 Environmental aging not only alters the size of plastic pieces but may also increase their density, and alter their colour and surface chemistry. 2,7,8 Nano- and microplastics are ubiquitous in our environment and have been found in surface waters, 9,10 soils, 11,12 ice cores, 13 urban center atmospheric fallout, 14,15 and remote terrestrial environments. 16–19…”

“…[3][4][5][6] Environmental aging not only alters the size of plastic pieces but may also increase their density, and alter their colour and surface chemistry. 2,7,8 Nano-and microplastics are ubiquitous in our environment and have been found in surface waters, 9,10 soils, 11,12 ice cores, 13 urban center atmospheric fallout, 14,15 and remote terrestrial environments. [16][17][18][19] Much of the work investigating environmental plastics has focused on the microplastic size range even though nanoplastics are expected to greatly outnumber microplastics.…”