Fig. 4: Relationships between the proportions of trimethylarsine oxide (TMAsVO) in precipitation (sub)events and contributing moisture sources, dissolved organic carbon content and the sea salt proxy.
From: Marine and terrestrial contributions to atmospheric deposition fluxes of methylated arsenic species
a shows the variability of TMAsVO proportions (% sum of arsenic (As) species concentrations) in the clusters C1-C4 defined by different contributing moisture sources in Fig. 3b. The boxplots show the interquartile range, representing the middle 50% of the data, which fall between the upper quartile (75% data below that score) and the lower quartile (less than 25% below that score). The whiskers refer to the 5th/95th percentiles. b and c show the variability of TMAsVO proportions as a function of dissolved organic carbon (DOC) and the sodium to strontium concentration ratio (Na:Sr, sea salt proxy), respectively. The size of data points corresponds to the DOC concentrations in precipitation samples. All symbols in b and c are colour coded according to moisture source clusters shown in Fig. 3b. Different letters (x, y) in a denote significance levels based on Mann-Whitney-U test (p < 0.05). For all clusters with the same letter, the difference between species proportion is not statistically significant. Indicated correlation coefficient in b is significant (n = 26, p < 0.05), the 90% confidence interval of the regression line (dashed line) is shown in grey, and the error bars represent the uncertainty of quantification by HPLC-ICP-MS/MS performed in duplicate (average relative standard deviation of TMAsVO measurements: 4 ± 3%), with invisible error bars indicating standard deviations within the symbol. The ellipses drawn around the points indicate suggested source contributions. The corresponding figure for dimethylarsinic acid (DMAsV) and inorganic As (iAs) is shown in Supplementary Fig. 10.
