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Improving the characterization of dissolved organic carbon in cloud water: Amino acids and their impact on the oxidant capacity

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ABSTRACT

Improving our understanding of cloud chemistry depends on achieving better chemical characterization (90% of the organic carbon [OC] fraction remains uncharacterized) and, consequently, assessing the reactivity of this complex system. In this manuscript, we report for the first time the concentrations of 16 amino acids (AAs) in 25 cloud water samples. The concentrations of individual AAs ranged from a few nM up to ~2.0 μM, and the average contribution of AAs corresponded to 9.1% (4.4 to 21.6%) of the dissolved OC (DOC) concentration. Considering their occurrence and concentrations, AAs were expected to represent an important hydroxyl radical (HO•) sink in aqueous cloud samples. In this work, we estimated that approximately 17% (from 7 to 36%) of the hydroxyl radical-scavenging ability of the DOC could be attributed to the presence of AAs, whereas comparing the AAs suggested that an average of 51% (from 22 to 80%) of their reactivity with HO• could account for the presence of tryptophan. These results clearly demonstrate that the occurrence and reactivity of AAs must be considered to better estimate the chemical composition and oxidant capacity of the cloud aqueous phase.

No MeSH data available.


HO• scavenging rates (k′) of AAs, TRP and DOC.These values were determined based on the average values of ,  and  using the concentrations and second-order rate constants reported in Tables S1 and S3. The  value was taken from Arakaki et al.39.
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f4: HO• scavenging rates (k′) of AAs, TRP and DOC.These values were determined based on the average values of , and using the concentrations and second-order rate constants reported in Tables S1 and S3. The value was taken from Arakaki et al.39.

Mentions: Figure 4 shows the contributions of all AAs, TRP and DOC to the scavenging rate constant of the hydroxyl radical in terms of their average concentrations. Up to 51% of the total reactivity of HO•, which is expressed as , was attributable to TRP (~ 6.76 ± 3.98 × 103 s−1) among all AAs ( ~1.28 ± 0.51 × 104 s−1). Interestingly the concentration of TRP was expected to be lower than those of other AAs because of its high reactivity with HO•, suggesting the presence of a possible source of TRP in cloud water28. Moreover, as recently reported, the oxidation of TRP in cloud waters led to the formation of formate and acetate in 20% yields, with other nitrogen derivatives also likely produced (up to 60% of the uncharacterized carbon)30. These findings demonstrated that TRP oxidation could be responsible for a large fraction of the HO• scavenged in natural samples.


Improving the characterization of dissolved organic carbon in cloud water: Amino acids and their impact on the oxidant capacity
HO• scavenging rates (k′) of AAs, TRP and DOC.These values were determined based on the average values of ,  and  using the concentrations and second-order rate constants reported in Tables S1 and S3. The  value was taken from Arakaki et al.39.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5120292&req=5

f4: HO• scavenging rates (k′) of AAs, TRP and DOC.These values were determined based on the average values of , and using the concentrations and second-order rate constants reported in Tables S1 and S3. The value was taken from Arakaki et al.39.
Mentions: Figure 4 shows the contributions of all AAs, TRP and DOC to the scavenging rate constant of the hydroxyl radical in terms of their average concentrations. Up to 51% of the total reactivity of HO•, which is expressed as , was attributable to TRP (~ 6.76 ± 3.98 × 103 s−1) among all AAs ( ~1.28 ± 0.51 × 104 s−1). Interestingly the concentration of TRP was expected to be lower than those of other AAs because of its high reactivity with HO•, suggesting the presence of a possible source of TRP in cloud water28. Moreover, as recently reported, the oxidation of TRP in cloud waters led to the formation of formate and acetate in 20% yields, with other nitrogen derivatives also likely produced (up to 60% of the uncharacterized carbon)30. These findings demonstrated that TRP oxidation could be responsible for a large fraction of the HO• scavenged in natural samples.

View Article: PubMed Central - PubMed

ABSTRACT

Improving our understanding of cloud chemistry depends on achieving better chemical characterization (90% of the organic carbon [OC] fraction remains uncharacterized) and, consequently, assessing the reactivity of this complex system. In this manuscript, we report for the first time the concentrations of 16 amino acids (AAs) in 25 cloud water samples. The concentrations of individual AAs ranged from a few nM up to ~2.0 μM, and the average contribution of AAs corresponded to 9.1% (4.4 to 21.6%) of the dissolved OC (DOC) concentration. Considering their occurrence and concentrations, AAs were expected to represent an important hydroxyl radical (HO•) sink in aqueous cloud samples. In this work, we estimated that approximately 17% (from 7 to 36%) of the hydroxyl radical-scavenging ability of the DOC could be attributed to the presence of AAs, whereas comparing the AAs suggested that an average of 51% (from 22 to 80%) of their reactivity with HO• could account for the presence of tryptophan. These results clearly demonstrate that the occurrence and reactivity of AAs must be considered to better estimate the chemical composition and oxidant capacity of the cloud aqueous phase.

No MeSH data available.