Laboratory development and field evaluation of a new diffusive sampler to collect nitrogen oxides in the ambient air

Abstract.

Diffusive samplers for the determination of NO_x and NO₂ based on collection on a coated carbon paper filter have been developed. NO is first oxidized to NO₂ and then collected on the reactive surface. When NO₂ and NO_x samplers are exposed simultaneously, NO can be calculated by difference. The sampler has been derived from a Palmes design as recently modified by Bertoni et al. for the determination of BTX (benzene, toluene, xylenes). Laboratory tests were conducted in controlled atmosphere to evaluate linearity, uptake rate, face velocity effects, sample stability, influence of relative humidity, precision and accuracy. The samplers are capable of reliable measurements of the two species at common levels of a polluted atmosphere in urban settings yielding average concentration levels over 1 month and beyond.

The uptake rate of NO₂ was found to be 11.7 mL/min in a very good agreement (within 5%) with the value calculated from theory. The measured uptake rate for NO_x was determined in experiments involving sampling at different concentration levels in comparison to chemiluminescence (CL) measurements. The precision of the measurements for co-located passive samplers was better than 5%. The accuracy of the data collected is within ±20% of the actual value measured by CL. The laboratory and field results show that the NO_x and NO₂ samplers meet the data quality goal requested by the first EU Directive 1999/30/EU for these pollutants.