Interactive comment on “Light-induced protein nitration and degradation with HONO emission”

Proteins can be nitrated by air pollutants (NO2), enhancing their allergenic potential. This work provides 15 insight into protein nitration and subsequent decomposition in the presencet of solar radiation. We also investigated 16 light-induced formation of nitrous acid (HONO) from protein surfaces that were nitrated either online with 17 instantaneous gas phase exposure to NO2 or offline by an efficient nitration agent (tetranitromethane, TNM). Bovine 18 serum albumin (BSA) and ovalbumin (OVA) were used as model substances for proteins. Nitration degrees of about 19 1% were derived applying NO2 concentrations of 100 ppb under VIS/UV illuminated condition, while simultaneous 20 decomposition of (nitrated) proteins was also found during long-term (20h) irradiation exposure. Measurements of 21 Ggas exchange measurements onf TNMnitrated proteins revealed that HONO can be formed and released even 22 without contribution of instantaneous heterogeneous NO2 conversion. However, fumigation with NO2 exposure was 23 found to increase HONO emissions substantially. In particular, a strong dependence of HONO emissions on light 24 intensity, relative humidity (RH), NO2 concentrations and the applied coating thickness were found. The 20 hours 25 long-term studies revealed sustained HONO formation, even if concentrations of the intact (nitrated) proteins were 26 too low to be detected after the gas exchange measurements. A reaction mechanism for the NO2 conversion based on 27 the Langmuir-Hinshelwood kinetics is proposed. 28