AIM-IC: Applications to nitrous acid (HONO) in the ambient atmosphere and precipitation monitoring

The Ambient Ion Monitor-Ion Chromatography (AIM-IC) instrument offers the ability to observe atmospheric constituents that form ionic species in aqueous solution. Applied to online analysis of the atmosphere, the AIM-IC achieves 1hr time resolution of 10 anion and 6 cation chemical species with sub-ppb detection of trace gases and 10-100 ng m-3 detection of particulate matter constituents.Continuous monitoring with the AIM-IC has provided observations of nitrous acid (HONO) and particulate nitrite (NO2-) in the urban atmosphere of Toronto, ON. Characterization of the NO2 interference in the AIM-IC has shown low artefact levels that are likely only important to consider during daylight hours where ambient HONO is low. Ambient observations have shown episodes of rapid nighttime accumulation of HONO and NO2 - to nearly equal abundances, particularly during periods of strong diurnal temperature change.A method for collection and offline analysis of precipitation has been developed simultaneously to examine the impact of precipitation scavenging as a sink of trace gases and particulate matter.