Minimizing sampling uncertainties associated with NOy measurements

Background/Question/Methods

Fossil fuel burning, land use change, and associated disturbance processes are anthropogenic forcings that enhance total reactive nitrogen (NO_y) emissions. Most ecosystems in North America are nitrogen limited. An overload of NO_y in such ecosystems can affect the photochemical production of ozone, the ecosystem’s nutrient status, and the transport of atmospheric nitrogen from localized boundary layers to the free atmosphere. It is for these reasons that the National Ecological Observatory Network (NEON) will measure atmospheric NO_y concentrations across the United States. Ultimately these measurements will be used to derive NO_y fluxes.

Accurate measurement of NO_y is a function of uncertainties inherent in the sampling design. Alleviating these uncertainties will better inform current knowledge of atmospheric and ecological responses to NO_y. Here, attention is given to the sampling design with the aim of investigating and minimizing the main variables directly influencing measurement uncertainty of atmospheric NO_y.

Results/Conclusions

The variables influencing measurement uncertainty of the sampling design are i) the length of sampling line between the inlet and the converter (catalyst), ii) the temperature and relative humidity of the sampling line, iii) the material of the sampling line, and iv) the frequency of calibration / validation of the system. The optimal sampling configurations that minimize measurement uncertainty will be used to design the reactive nitrogen measurement systems at NEON. More accurate measurements of atmospheric NO_y concentrations and fluxes will result from this research, allowing ecosystem processes involving reactive nitrogen to be examined on a continental scale.