Abstract
Recently, deteriorating ozone (O(3)) pollution in China brought the precise diagnosis of O(3) sensitive chemistry to the forefront. As a dominant precursor of OH radicals, atmospheric nitrous acid (HONO) plays an important role in O(3) production. However, its measurement unavailability in many regions especially for second- and third-tier cities may lead to the misjudgment of the O(3) sensitivity regime derived from observation-based models. Here, we systematically assess the potential impact of HONO on diagnosing the sensitivity of O(3) production using a 0-dimension box model based on a comprehensive summer urban field campaign. The results indicated that the default mode (only the NO + OH reaction is included) in the model could underestimate ∼87% of observed HONO levels, leading to an obvious decrease (∼19%) of net O(3) production in the morning, which was in line with the previous studies. The unconstrained HONO in the model was found to significantly push O(3) production toward the VOC-sensitive regime. Additionally, it is unrealistic to change NO (x) but constrain HONO in the model due to the dependence of HONO formation on NO (x) . Assuming that HONO varied proportionally with NO (x) , a stronger NO (x) -sensitive condition could be achieved. Therefore, effective reduction of NO (x) should be given more attention together with VOC emission control for O(3) mitigation.