NO2 and HONO concentrations measured with filter pack sampling and high HONO/NO2 ratio in Ho Chi Minh city, Vietnam

Nitrogen dioxide and nitrous acid (HONO) in the atmosphere were simultaneously measured with a filter pack (FP) method in Ho Chi Minh City, Vietnam (HCM), in 2017 and 2018. To collect NO2 effectively, the absorption performance of NO2 by the FP method with a triethanolamine (TEA)-impregnated filter was improved. After HNO3 and HONO in the sample air were collected by NaCl and Na2CO3 impregnated filters, respectively, at 2.0 or 4.0 dm3 min−1, NO2 was collected. The air flow was divided into two lines after the HNO3 and HONO filter pack, and one line was used for collecting NO2. With a 0.1 dm3 min−1 flow rate and 20 wt% TEA in the impregnating solution, the collection efficiency of NO2 was almost 100%. The present method was applied for the measurement of HONO and NO2 in HCM in August 2017 and 2018. The average concentrations (29–48 h average) of NO2 and HONO were 17.1 ± 5.7 ppb (average ± 1 standard deviation) and 2.2 ± 0.6 ppb, respectively. The average HONO/NO2 ratio of 13.4 ± 3.5% was significantly higher by a considerable margin than reported values in the literature.