Observations of NOy, CO, and SO2 and the origin of reactive nitrogen in the eastern United States

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Abstract
We have developed a technique to quantify better the relative significance of reactive nitrogen sources at a given site by measuring NOy, SO2, and CO. Measurements taken on Maryland's eastern shore of the Chesapeake Bay indicate that, on average, a minimum of 20% of the NOy is coming from coal‐fired point sources. Measurements in Shenandoah National Park, Virginia, and near Arendtsville, Pennsylvania, indicate that these minimum fractions are 34% and 32%, respectively. The remainder is coming predominantly from mobile sources, though there are some NOy sources whose influence cannot be determined with this technique. If the emissions inventories are taken to be correct, half the emitted NOy has been lost (probably deposited as nitrate) by the time it reaches the site. Analysis of air parcel back trajectories reveals that the likely source of elevated SO2 levels, and therefore point source emissions of NOy, is the industrialized Midwest of the United States.