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

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.


Distribution of each AA in the cloud samples.The bottom and top lines of the box correspond to the 25th and 75th percentiles, respectively. The middle line represents the median. The ends of the whiskers are the 10th and 90th percentiles, and the filled circle is an outlier. The y-right scale shows the total AA concentration.
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f1: Distribution of each AA in the cloud samples.The bottom and top lines of the box correspond to the 25th and 75th percentiles, respectively. The middle line represents the median. The ends of the whiskers are the 10th and 90th percentiles, and the filled circle is an outlier. The y-right scale shows the total AA concentration.

Mentions: Figure 1 illustrates the concentrations of each AA in the cloud samples, showing that the average concentrations of ILE, PHE, SER and TRP exceeded 0.25 μM (see Table 1 for the AA abbreviations and relative concentrations). The median values of the single-AA concentrations were lower than 0.5 μM, and concentrations of ILE and TRP were the highest, with an average value of 0.3 and 0.4 μM respectively. The total AA concentration, defined as the median value of the sum of the AA concentration in each sample, ranged from 1 to 4 μM. The average concentrations of AA in cloud water samples were lower than those measured in fog water by Zhang et al.13 (2.6–99 μM, mean ± 1σ = 20 ± 27 μM) and in dew water samples in Germany by Scheller32 (0.5–110 μM, mean = 22.5 μM). The concentrations found here were relatively similar to those reported in rainwater by Gorzelska et al.33 (≈ 0.4 μM) and Mopper and Zika34 (6.5 μM). Fog and dew water were expected to be more concentrated than cloud water because they are influenced relatively strongly by local sources and lead to less dilution of particle compared to the cloud droplets. The sampling procedure may also have contributed to this difference because of the potential evaporation of the liquid sample. The high TRP concentration cannot be directly correlated to the hydrolysis of proteinaceous matter. However, TRP was recently demonstrated to be strongly correlated with the formation of high-molecular-weight compounds with spectroscopic characteristics similar to those of HULIS, which can also be considered as a potential TRP reservoir3035. Muller et al.36 evaluated TRYptophan LIke Substances (TRYLIS) in rain using fluorescence emission. These authors found that the TRP concentration was higher in samples from marine origins, suggesting that the presence of TRYLIS promoted the development of ice-precipitation at ‘warmer’ temperatures. Nevertheless, the detection of this compound in the fluorescence matrix was not suitable for the discrimination of free and combined TRP.


Improving the characterization of dissolved organic carbon in cloud water: Amino acids and their impact on the oxidant capacity
Distribution of each AA in the cloud samples.The bottom and top lines of the box correspond to the 25th and 75th percentiles, respectively. The middle line represents the median. The ends of the whiskers are the 10th and 90th percentiles, and the filled circle is an outlier. The y-right scale shows the total AA concentration.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: Distribution of each AA in the cloud samples.The bottom and top lines of the box correspond to the 25th and 75th percentiles, respectively. The middle line represents the median. The ends of the whiskers are the 10th and 90th percentiles, and the filled circle is an outlier. The y-right scale shows the total AA concentration.
Mentions: Figure 1 illustrates the concentrations of each AA in the cloud samples, showing that the average concentrations of ILE, PHE, SER and TRP exceeded 0.25 μM (see Table 1 for the AA abbreviations and relative concentrations). The median values of the single-AA concentrations were lower than 0.5 μM, and concentrations of ILE and TRP were the highest, with an average value of 0.3 and 0.4 μM respectively. The total AA concentration, defined as the median value of the sum of the AA concentration in each sample, ranged from 1 to 4 μM. The average concentrations of AA in cloud water samples were lower than those measured in fog water by Zhang et al.13 (2.6–99 μM, mean ± 1σ = 20 ± 27 μM) and in dew water samples in Germany by Scheller32 (0.5–110 μM, mean = 22.5 μM). The concentrations found here were relatively similar to those reported in rainwater by Gorzelska et al.33 (≈ 0.4 μM) and Mopper and Zika34 (6.5 μM). Fog and dew water were expected to be more concentrated than cloud water because they are influenced relatively strongly by local sources and lead to less dilution of particle compared to the cloud droplets. The sampling procedure may also have contributed to this difference because of the potential evaporation of the liquid sample. The high TRP concentration cannot be directly correlated to the hydrolysis of proteinaceous matter. However, TRP was recently demonstrated to be strongly correlated with the formation of high-molecular-weight compounds with spectroscopic characteristics similar to those of HULIS, which can also be considered as a potential TRP reservoir3035. Muller et al.36 evaluated TRYptophan LIke Substances (TRYLIS) in rain using fluorescence emission. These authors found that the TRP concentration was higher in samples from marine origins, suggesting that the presence of TRYLIS promoted the development of ice-precipitation at ‘warmer’ temperatures. Nevertheless, the detection of this compound in the fluorescence matrix was not suitable for the discrimination of free and combined TRP.

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.