Atmospheric particulate deposits onto outdoor surfaces creating environmental films reflecting the local climate and pollution conditions. Chemical analyses of these films have shown how seasonal changes impact their makeup, but there is still much to learn about the morphology. Different physical forms of molecular species exhibit different reactivity. We have collected samples in two-month intervals over a time period of 24 months, analyzed their chemical makeup and changes in interfacial chemical functionality with exposure to high relative humidity (RH%). Bright field microscopy is used to report surface coverage, identify microorganism growth, and report density of deposited particles. Results show that warmer months encourage higher biotic activity. We also see higher chloride concentrations in winter months suggesting that road salting affects film composition. Warmer months have higher amounts of total dissolved solids (TDS) measurements suggesting summer films may contribute more mass to water run-off during rain events than winter films. Interfacial spectroscopy traces salts (sulfates and nitrates) within the films. Increasing RH% (from ca. 0% to 70%) causes films to absorb significant amount of water. In films with higher NOx content, we see increasing of water-associated -OH stretching (3250cm-1) but also increased nitrate stretching (1320 and 1420cm-1). This has implications of higher contributions to NOx chemistry. Overall, we have seen that the collected environmental films’ surface coverage, chemical makeup, and rain discharge vary with seasonality. These results will help us understand how to predict the impact of environmental films over different seasons, allowing them to be built into current environmental models.

Seasonality studies of collected environmental films using interfacial spectroscopy

ACS Fall 2021

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