Development of stripping coil-ion chromatograph method and intercomparison with CEAS and LOPAP to measure atmospheric HONO

Abstract

Nitrous acid (HONO) is the major precursor of OH radicals in polluted areas. Accurate measurement of HONO provides vital evidence for exploring the formation of secondary pollution. Stripping coil (SC) equipped with ion chromatograph (IC) or spectrograph as one of wet chemical methods has been already used to measure HONO. The reliability of the method mainly depends on the collection efficiency and the interference from other species. In this study, a SC-IC method was set up to measure HONO. The performance of the method was assessed in the chamber using two kinds of absorption solutions i.e. ultrapure water and 25 μM Na2CO3 solution under different concentrations of SO2. Results indicated that HONO concentrations absorbed by ultrapure water and Na2CO3 solution were almost identical in the absence of SO2 in the chamber and both the collection efficiencies were >99%. However, the collection efficiency of ultrapure water decreased with the increase of SO2, indicating that the presence of SO2 resulted in the penetration of HONO. The collection efficiency kept >90% when the concentration of SO2 was no >23 ppbv. Comparing with the situation without SO2, HONO performed a remarkable increase with the presence of SO2 when using Na2CO3 absorption solution, indicating that the extra generation of HONO from the reaction between SO2 and NO2 in alkaline solution. Consequently, ultrapure water as the absorption solution could provide a high collection efficiency and avoid the interferences from SO2 when the concentration of SO2 was below 23 ppbv. High correlations (slope = 0.94–1.06, r2 > 0.90) were found during the intercomparisons between SC-IC and other three techniques, suggesting the SC-IC method developed in this study was able to measure atmospheric HONO in the field campaigns.