Received: 24 Jun 2016 – Discussion started: 25 Jul 2016 – Revised: 27 Oct 2016 – Accepted: 05 Nov 2016 – Published: 22 Nov 2016
Abstract. Characterization of daytime sources of nitrous acid (HONO) is crucial to understand atmospheric oxidation and radical cycling in the planetary boundary layer. HONO and numerous other atmospheric trace constituents were measured on the Mediterranean island of Cyprus during the CYPHEX (CYprus PHotochemical EXperiment) campaign in summer 2014. Average volume mixing ratios of HONO were 35 pptv (±25 pptv) with a HONO ∕ NOx ratio of 0.33, which was considerably higher than reported for most other rural and urban regions. Diel profiles of HONO showed peak values in the late morning (60 ± 28 pptv around 09:00 local time) and persistently high mixing ratios during daytime (45 ± 18 pptv), indicating that the photolytic loss of HONO is compensated by a strong daytime source. Budget analyses revealed unidentified sources producing up to 3.4 × 106 molecules cm−3 s−1 of HONO and up to 2.0 × 107 molecules cm−3 s−1 NO. Under humid conditions (relative humidity > 70 %), the source strengths of HONO and NO exhibited a close linear correlation (R2 = 0.72), suggesting a common source that may be attributable to emissions from microbial communities on soil surfaces.
There are many studies which show discrepancies between modeled and measured nitrous acid (HONO, precursor of OH radical) in the troposphere but with no satisfactory explanation. Ideal conditions to study the unknown sources of HONO were found on Cyprus, a remote Mediterranean island. Budget analysis of trace gas measurements indicates a common source of NO and HONO, which is not related to anthropogenic activity and is most likely derived from biologic activity in soils and subsequent emission.
There are many studies which show discrepancies between modeled and measured nitrous acid (HONO,...
