Overestimation of urban nitrogen dioxide by passive diffusion tubes: a comparative exposure and model study

摘要: Abstract A detailed comparative trial of passive diffusion tubes (PDT) for measurement NO 2 in urban air has been undertaken Edinburgh, UK. Acrylic, foil-wrapped and quartz were exposed parallel 1-week 4-week periods at three sites equipped with continuous analysers NO, x O 3 . Standard acrylic PDTs significantly overestimated concentrations relative to chemiluminescence analysers, by an average 27% over all exposures. No significant difference was observed between standard (both UV blocking). The mean ratio (UV transmitting) 1.06. Quartz PDT data suggest a tendency situ photolysis offset (but non-quantifiable way) the effect chemical overestimation. exposures yielded systematically lower concentration than from four sequential same period. reduction apparent sampling rate time mostlikely arises trapped Hourly , 20 used as input numerical model tube operation incorporating reaction co-diffusing within tube. calculated overestimation 22% simulations is close analyser (24% exposure periods), showing that within-tube chemistry can account discrepancies two techniques. Overestimation generally increased /NO ratios decreased. Accurate quantitative correction measurements not possible. Nevertheless, correlated both suggesting retain qualitative measure variation particular location.