Contribution of biogenic nitric oxide in urban ozone: Raleigh, NC, as a case study

Anthropogenic emissions from industrial and automotive sources within the confines of the city of Raleigh, NC have been documented by the North Carolina Department of Environment, Health and Natural Resources, Division of Environmental Management, but no direct biogenic emissions of nitric oxide (NO) from soils has yet been measured. In this study, emissions of NO were measured in Raleigh, NC, and its surrounding suburbs, in an attempt to determine the portion of the total NOx ( = NO + NO2) budget which can be attributed to biogenic sources. Residential and commercial lawns, and golf courses receiving normal fertilizer applications were chosen as the primary biogenic source of NO. Soil NO fluxes were measured using a dynamic chamber technique from 11 sites and ranged in value (hourly averages calculated from 15 min readings) from 1.24 to 23.7 ng N m−2 s−1. These hour averages were then combined with estimates of lawn acreage within the city proper, and in the surrounding suburbs, in order to develop a budget for giogenic NO emissions in Raleigh. This budget was then compared to the budget used in the Environmental Protection Agencyʹs (EPA) Regional Oxidant Model (ROM) for photochemical modeling. Results from this comparison suggest that less than 1 % of the total NOx budget for Raleigh, NC is emitted by natural processes, and that approximately 1.2% of the nitrogen applied as fertilizer is lost via soil NO emissions. Thus, the effects of biogenic NO may be neglected in the development of a reliable plan for reducing ozone in the urban atmosphere.