Comment on egusphere-2023-1072

Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> Particulate Free amino acids (FAAs) are essential components of organonitrogen that have critical climate impacts, but they are usually considered stable end products from protein degradation. In this work, we investigated the decay glycine (GC) as a model FAA under photolysis of different particulate nitrate salts using an in-situ micro-Raman system. Upon changes of the relative humidity (RH) cycle between 3 and 80 % RH, ammonium nitrate (AN)+GC mixed particles did not exhibit any phase change, whereas sodium nitrate (SN)+GC mixed particles crystallized at 60 % and deliquesced at 82 % RH. Under light illumination at 80 % RH, AN+GC particles showed almost no spectral changes, while rapid decays of glycine and nitrate were observed in SN+GC particles. The interactions between nitrate and glycine in AN+GC particles suppressed crystallization, but also hindered nitrate photolysis and glycine decay. On the other hand, glycine formed a complex with Na⁺ in deliquescent SN+GC particles and allowed unbonded nitrate to undergo photolysis and trigger glycine decay, though nitrate photolysis was greatly hindered upon particle crystallization. Our work provides insights into how FAAs may interact with different nitrate salts under irradiation and lead to distinct decay rates, which facilitates further investigations on their atmospheric lifetime estimation.