Measurement of air-surface exchange of speciated nitrogen and sulfur compounds in a coastal environment

Ian Rumsey1 and John T. Walker2

Ecosystem exposure and vulnerability to atmospheric deposition of nitrogen and sulfur compounds is increasingly being assessed by the United States Environmental Protection Agency’s (U.S. EPA’s) primary regulatory tool, the Community Multiscale Air Quality Model (CMAQ). Further development of the model’s dry deposition algorithms requires observational datasets across a range of different conditions including variations in meteorology, atmospheric chemistry and surface conditions. Observational datasets for coastal environments, which often have different meteorological and atmospheric chemistry conditions in comparison to inland, have historically been data-limited with respect to direct dry deposition measurements. Therefore, such datasets, will help determine the influence of coastal atmospheric physical and chemical processes on speciated dry nitrogen and sulfur deposition. In this study, the Monitor for AeRosols and GAses in ambient air (MARGA) instrument is deployed in a coastal environment near Charleston, South Carolina. The MARGA is an on-line ion-chromatography-based measurement instrument which simultaneously measures multiple gas and aerosol species at an hourly resolution, allowing the opportunity to develop long term multi-species air-surface exchange measurements. This study uses the MARGA 2S system, which includes two sampling boxes interfaced to a single analytical instrument. Concentration measurements are used in conjunction with the micrometeorological aerodynamic gradient method to determine air-surface exchange fluxes of gases (NH3, HNO3, HNO2, and SO2) and aerosols (NH4+, NO3-, and SO42-). The presentation describes preliminary measurements of air concentrations and fluxes above a grass field, during the late summer and fall of 2016. The general features of compound-specific concentrations and fluxes, including relationships with atmospheric physical and chemical processes, are discussed. 


1College of Charleston,
2U.S. EPA,