The γ decreased with increasing the O2 content and the O3 concentration. The HONO yield was found to be independent of the O2 content. The HONO yield inversely depended on the O3 concentration. Aging of HA by O2 and O3 led to the lower reactivity of HA toward NO2. Mechanism of effects of O2 and O3 on the reaction of NO2 with HA was discussed.