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Biodegradable plastic mulch films (BDMs) are essential in the production of vegetable and specialty crops due to their promotion of increased crop yield and quality. Unlike conventional polyethylene (PE) mulches, BDMs can be tilled into the soil after crop harvest to undergo biodegradation, thereby leading to minimal environmental impact. Agricultural weathering impacts both the performance of BDMs during crop production as a barrier to weeds and biodegradability of BDMs in the soil. To better understand the relative importance of climatic factors, the change of physicochemical properties of BDMs during single-season, 3-4 month, field trials for vegetable production at two diverse climates (Knoxville, TN and Mount Vernon, WA) across four successive years (2015-2018) was evaluated. Mulch treatments consisted of four commercially available BDMs composed primarily of polybutylene co-adipate-co-terephthalate (PBAT) that differed in color and polymeric feedstock, a black experimental BDM prepared from polylactic acid/polyhydroxybutyrate (PLA/PHA) blend, and conventional PE mulch. Solar radiation, an important factor to degradation of mulches, was higher in WA than TN in most sampling years. Yet, degradation occurred more greatly for BDMs in TN, which is attributable to higher temperatures in TN. Mulch deterioration did not very extensively between years. Loss of mechanical properties and color was greater than chemical property changes. Differences in the extent of molecular weight decrease between years correlated significantly with solar radiation exposure at the two locations. A black-colored PBAT-based BDM was less susceptible to degradation than equivalent clear and white-on-black films, due to carbon black acting as a photostabilizer. The impact of weathering also differed between three commercially available PBAT-based films. The PLA/PHA mulch was more susceptible to degradation than PBAT-based BDMs, particularly in the warmer location, TN, partially due to a leaching out of PHA and lower-molecular weight polymer molecules. The extent of change for physicochemical properties of BDMs due to agricultural weathering is greatly affected by polymeric composition, and is greater in warmer climates. Keywords Agricultural (environmental) weathering • Biodegradable plastic mulch film • Mulch degradation • Polylactic acid (PLA) • Polybutylene co-adipate-co-terephthalate (PBAT)

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Abstract. Organic sulfur and sulfate compounds, tracers for sources and atmospheric processes, are not currently measured in national monitoring networks such as the Interagency Monitoring of Protected Visual Environments (IMPROVE). The goal of this paper is to begin to assess the stability of organic sulfur and sulfate containing compounds on polytetrafluoroethylene (PTFE) filters and the suitability of Fourier-transform infrared (FT-IR) spectroscopy to measure these compounds. Stability assessment is needed because PTFE samples collected by IMPROVE are typically stored 6–9 months prior to analysis. For this study, two organosulfur compounds, methanesulfonic acid (MSA) and hydroxymethanesulfonate ion (HMS), and two organosulfate compounds, methyl sulfate (MS) and 2-methyltetrol sulfate (2-MTS), are collected individually on PTFE filters. Gravimetric mass measurements is used to assess mass stability over time. FT-IR spectra are evaluated to assess the capability of measuring the compound from PTFE filters by assessing the compound stability or chemical changes over time. Ion chromatography (IC) and Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) are used as an additional tool to assess stability or chemical changes over time. MS has the highest potential to be measured by FT-IR in IMPROVE samples. For MS, a simple organosulfate, the mass changes are within measurement uncertainty and FT-IR spectra indicate no compositional change over a 4-month period, suggesting MS can be measured using FT-IR. IC and ICP-OES support the conclusion that MS is stable on the filter. However, for 2-MTS, the other organosulfate measured in this study, spectral changes after a month on the filter suggests it decomposes into other organosulfates or an inorganic sulfate. MSA in IMPROVE samples can be measured, but only as a lower bound, due to volatility off of the filter as indicated by FT-IR and gravimetry. FT-IR and IC both show that MSA is not chemically changing over the course of the study. Measurements by all methods indicate HMS is unstable on PTFE filter and IC and FT-IR indicate that it likely converts to inorganic sulfate. Future work includes the evaluation of these compounds in as ambient aerosol sample matrix to determine any differences in stability and identify interferences that could limit quantification.

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