Abstract
Abstract. The sinks of hydrocarbons in the atmosphere are usually described by oxidation reactions in the gas and aqueous (cloud) phases. Previous lab studies suggest that in addition to chemical processes, biodegradation by bacteria might also contribute to the loss of organics in clouds; however, due to the lack of comprehensive data sets on such biodegradation processes, they are not commonly included in atmospheric models. In the current study, we measured the biodegradation rates of phenol and catechol, which are known pollutants, by one of the most active strains selected during our previous screening in clouds (Rhodococcus enclensis). For catechol, biodegradation is about 10 times faster than for phenol. The experimentally derived biodegradation rates are included in a multiphase box model to compare the chemical loss rates of phenol and catechol in both the gas and aqueous phases to their biodegradation rate in the aqueous phase under atmospheric conditions. Model results show that the degradation rates in the aqueous phase by chemical and biological processes for both compounds are similar to each other. During day time, biodegradation of catechol is even predicted to exceed the chemical activity in the aqueous phase and to represent a significant sink (17 %) of total catechol in the atmospheric multiphase system. In general, our results suggest that atmospheric multiphase models may be incomplete for highly soluble organics as biodegradation may represent an unrecognized efficient loss of such organics in cloud water.
Highlights
Monocyclic aromatic compounds in the atmosphere are of great interest due to their influence on ozone formation (Hsieh et al, 1999) and their potential to form secondary organic aerosol (Ng et al, 2007)
We have demonstrated that pH variation has a low impact on microbial biodegradation ability, as was shown in the case of carboxylic acids by 17 strains isolated from clouds (Vaïtilingom et al, 2011) or phenol by Pseudomonas aeruginosa (Razika et al, 2010)
This insensitivity to the solution pH can be explained by the fact that the biodegradation experiments are performed with bacteria and not purified enzymes
Summary
Monocyclic aromatic compounds in the atmosphere are of great interest due to their influence on ozone formation (Hsieh et al, 1999) and their potential to form secondary organic aerosol (Ng et al, 2007). Their main sources include combustion processes of coal, oil and gasoline. Phenol’s much higher water solubility (KH = 647 M atm−1) as compared to benzene (KH ∼ 0.2 M atm−1) leads to nanomolar levels in cloud water: 5.5–7.7 nM at the Puy de Dôme (France) (Lebedev et al, 2018), 30–95 nM at Great Dun Fell (Lüttke et al, 1997), and 37 nM in the Vosges Mountains (Levsen et al, 1993). Phenolic compounds have been shown to comprise 2 %–4 % of the total organic particulate matter at several locations in the northeastern US
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