<p>Nitrogen compounds such as nitrogen dioxide (NO<sub>2</sub>) and ammonia (NH<sub>3</sub>) contribute significantly to air pollution and environmental degradation. Fine-grained networks of sensors for ambient nitrogen compounds can be used to inform policy makers and farmers about the effectiveness of techniques to reduce emissions of nitrogen compounds. We are developing a low-cost self-sustaining sensor system that can be deployed outdoors in large numbers in and around agricultural areas to measure the concentration of NH<sub>3</sub>, NO<sub>2</sub>, temperature and humidity with a high spatiotemporal resolution. We use off-the-shelf electrochemical sensors to measure nitrogen compounds. A preliminary comparison between the NH<sub>3</sub> measurements taken by our sensor system and by a differential optical absorption spectroscopy instrument (miniDOAS) demonstrate encouraging results. After calibration, the measurements from our system show fairly good agreement with hourly-averaged miniDOAS measurements, at concentrations down to ~20 µg/m<sup>3</sup>. We are currently setting up a larger validation study to further assess the performance and robustness of our system in different outdoor agricultural environments. Our sensor system has the potential to greatly expand the availability and affordability of NH<sub>3</sub> monitoring across wide areas, enabling farmers and policymakers to gain insights on the effectiveness of potential nitrogen reduction measures.</p>