Abstract
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.
Highlights
Air pollution, with its short- and long-term impacts on environment and human health, has been a globally recognized problem due to rapid population growth, industrialization and urbanization in recent decades
In order to assess the collection efficiency of Annular denuder system (ADS) with coating solution (Na2CO3 - glycerine in water/methanol) under tropical conditions with high ambient temperature and relative humidity, two sequential pairs of ADS was deployed with flow rate 20 L/min at National University of Singapore (NUS) atmospheric research station and five samples were collected on daily basis right before each round robin test
The Reynolds number, Re, which in a laminar stream must be less than 2000, was calculated as where γ is the kinematic viscosity of air, d1 and d2 are the internal and external diameters of the annulus, F is the flow rate; based on the data obtained from the pre-experimental period, Re was calculated as around 400
Summary
With its short- and long-term impacts on environment and human health, has been a globally recognized problem due to rapid population growth, industrialization and urbanization in recent decades. Nitrogen dioxide (NO2) and sulfur dioxide (SO2) are the most monitored criteria air pollutants in ambient air because of their effects on the human respiratory system, their contributions to the acidification of the ecosystems, the acidity of airborne particulate matter and its health impacts and the role of NO2 in the formation of photochemical oxidants (Plaisance et al, 2002; Cox, 2003). Both NO2 and SO2 can impact visibility as their corresponding oxidation products are incorporated into ambient aerosols. Routine monitoring of NO2 and SO2 at a global network of sampling locations with reliable measurement methods is needed to investigate both temporal and spatial changes in air quality on local to global scales (Lefohn and Shadwick, 1991; Hewitt, 2001)
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