Amines play important roles in atmospheric chemistry by acting as precursors to carcinogenic products (e.g., nitrosamines) and contributing to particle formation and growth. Due to these important roles, both natural and anthropogenic sources of amines to the atmosphere have been extensively catalogued. In this study, we explored the potential for the agricultural application of amines as herbicide-amine salts to contribute as a previously unrecognized source of atmospheric amines. In agriculture, amines (e.g., dimethylamine, DMA; isopropylamine, IPA) are frequently included in formulations of common herbicides (e.g., glyphosate, 2,4-D, dicamba) to increase herbicide solubility and/or reduce the vapor pressure of semi-volatile herbicides (i.e., dicamba) that volatilize themselves. Because herbicide-amine salts are sprayed as droplets that deposit and dry on soil and leaf surfaces, we first demonstrated that DMA volatilized both during drying of a solution containing equimolar 2,4-D as well as from the residue phase generated after drying. We found that both DMA and IPA volatilized when included in salts of all three common herbicides at equimolar concentrations during and after drying, indicating the generalizability of this phenomenon across herbicide-amine salts. Using U.S. herbicide use rates, we estimated the potential for herbicide-amine salts to serve as significant sources of amines to the atmosphere. We determined that approximately 4 Gg N of amine is applied agriculturally in the U.S. annually, primarily as highly volatile DMA and IPA, suggesting that herbicide-amine salts may act as important regional sources for atmospheric amines particularly in rural areas. While the estimated contribution by herbicide-amines is small relative to the global flux of amines to the atmosphere, which is estimated to be 285 Gg N global input of amines, our calculation only considers U.S. herbicide use, which accounts for ~12% of the worldwide value. Information on global herbicide use would better constrain the contribution of herbicide-amine salts relative to overall amine inputs into the atmosphere.

Amine volatilization from herbicide salts as an unrecognized source of amines to the atmosphere

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