Evaluation of Detection Efficiency of HONO, HNO₃, and SO₂ by a MARGA Wet Rotating-Denuder

Atmospheric gaseous compounds emitted from fossil fuel combustions and vehicles have a great impact on atmospheric chemistry by producing secondary aerosols via chemical reactions in the atmosphere or acting as precursors for tropospheric ozone formation. To fully understand chemical reaction mechanisms of secondary aerosols and ozone, accurate measurements of precursor gases are required. MARGA (Monitor for AeRosols and Gases in Ambient Air) is widely used for online monitoring of precursor gases such as HONO, HNO3, SO2, and NH3. In this study, the detection efficiency of a 2060 MARGA was evaluated by comparing with an offline sampling using an annular denuder followed by an ion chromatography analysis during 25 November 2021 similar to 17 February 2022. It was found that the detection efficiencies of precursor gases by the 2060 MARGA were significantly lower than those by the annular denuder system. SO2 and HONO concentrations measured by the 2060 MARGA were 62.3% and 49.9%, respectively, lower than those by the annular denuder system whereas HNO3 was 11.8% lower. This study also found that adsorption losses of these gases on the inner surface of sampling lines couldn't explained the difference between these two methods.