Measurements of NOx in Remote & Polluted Environments

A laser induced fluorescence instrument was tested for NOx measurements. Laboratory tests at the University of York indicated that the instrument could be efficiently used for NO2 measurements in a polluted atmosphere, with the installation of a gas phase titration system also showing promising results for NO characterisation. However, deployment at the Cape Verde Atmospheric Observatory for measurements in the remote marine boundary layer resulted in a significant over-estimation of NO2 mixing ratios. The LIF instrument measured NO2 levels that were around 8 times higher than those measured by a standard chemiluminescence analyser. The measurement inaccuracy was concluded to be a result of some kind of leak within the instrument. This meant that NO2 in the laboratory would also have been detected, resulting in greatly enhanced mixing ratios than would have been expected. This led to the conclusion that, in its current configuration, the instrument would not be suitable for long-term NO2 measurements in the remote boundary layer. This, along with consumable restrictions meant that the laser induced fluorescence was not used for NO measurements at the Cape Verde Atmospheric Observatory.
A photolytic chemiluminescence analyser was used to measure NOx emissions from oil and gas rigs in the North Sea as part of the airborne “Oil and Gas” campaign in the summer of 2015. Substantial NOx enhancements were observed during the campaign, with numerous exceedances of 10,000 pptv (10 ppbv). The direct integration method was used to derive NOx emissions coming from a specific set of rigs in the North Sea. These were then scaled up to evaluate the NAEI estimates for the whole North Sea drilling region. This study found that the NOx emissions from oil and gas rigs in the North Sea are poorly represented by the NAEI, with over 40,000 tons per year being unaccounted for. Such a substantial discrepancy highlights the need for regular assessment of inventory estimates, as these provide a basis for air quality directives and legislation, which in turn, are put in place to protect and improve local and regional air quality.