Nitrogen Oxide Emissions from Stationary Sources (Ion Chromatographic Method) – USEPA Method 7A

USEPA Method 7A is used for the determination of nitrogen oxide (NOx) emissions from stationary sources.
 
A grab sample is collected in an evacuated flask containing a dilute sulfuric acid-hydrogen peroxide absorbing solution.  The nitrogen oxides, excluding nitrous oxide (N₂O), are oxidized to nitrate and measured by ion chromatography.
 
Biased results are observed with this method when sampling under conditions of high sulfur dioxide concentrations (above 2000 ppm).