Comparison of NO₂ and SO₂ measurements using different passive samplers in tropical environment

This report describes the results of an inter-comparison study conducted for the sampling and analysis of NO₂ and SO₂ by using different type of passive samplers in tropical urban environment. For this purpose, field experiments were proposed to be conducted by two round robin tests from Sept. 2007 to Aug. 2008 in Singapore. A set of different types of passive samplers have been exposed to ambient air at atmospheric research station in National University of Singapore along with suitable active samplers (as reference method) for a sufficient period of time (3-4 weeks). Annular denuder system (ADS) active sampling data showed that NO₂ concentration level (23.8-28.1 ppb) in Singapore was slightly higher than the WHO guideline but SO₂ concentration (12.5-14.9 ppb) was approximately twice the value of WHO guideline. For the two round robin tests, accuracy analysis by using active sampling data as reference demonstrated that grand mean values from passive air sampling (PAS) and active sampler average concentrations, for both NO₂ and SO₂, are in close agreement with each other. Precision evaluation based on the triplicate samplers co-located at the same sampling site - Singapore showed that most of the passive samplers applied here had repeatability. ANOVA statistical analysis also showed no significant difference between the measurement data obtained by different type of passive samplers for both round robin tests in Singapore.