Simultaneous Sampling of NO, NO2, HONO and HNO3 in the Atmosphere by a Filter-Pack Method

Abstract

A simultaneous sampling method for gaseous nitric oxide (NO), nitrogen dioxide (NO₂), nitrous acid (HONO) and nitric acid (HNO₃) was developed by a filter-pack sampling method to measure these concentrations at low cost in areas where monitoring stations are not available or at multiple locations. HONO and HNO₃ gases were collected with a conventional filter-pack method. NO₂ was collected with a guaiacol-impregnated filter at a flow rate of 0.3 dm³ min⁻¹. NO was collected using guaiacol by oxidizing it to NO₂ with potassium permanganate at a 0.3 dm³ min⁻¹ flow rate. The optimum concentration of KMnO₄ in the immersion solution for the impregnated filter was 0.16 mol dm⁻³ (in 0.51 mol dm⁻³ H₂SO₄). The concentrations of NO and NO₂ measured by the filter-pack method were in good agreement with those measured by the chemiluminescence method. It was calculated that 60 ppb NO could be oxidized to NO₂ with the KMnO₄-impregnated filter for 183 hours at a 0.3 dm³ min⁻¹ flow rate. This is enough time for sampling in a real environment. This method was applied to measure NO, NO₂, HONO and HNO₃ in the atmosphere at three points around Osaka, Japan.