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Solubility and speciation of atmospheric iron in buffer systems simulating cloud conditions
Abstract The solubility of iron (Fe) in atmospheric particulate matter (PM) is important to understand its chemistry and potential bioavailability to ocean phytoplankton. However, current studies on Fe solubility and its speciation are highly uncertain partly due to inconsistencies in analytical protocols. In this study, cloud-processing of atmospheric PM was simulated in acetate, formate, and oxalate buffers (pH=4.30±0.05) at 0.5, 1, 5, and 20mM. Colorimetric analysis of Fe(II)–ferrozine complex showed that Fe solubility increased by an order of magnitude when acetate and formate concentrations increased from 0.5mM to 5mM, with a higher fraction of soluble Fe in acetate than in formate at lower buffer concentration (0.5mM). Measured pH of sample extracts revealed that weak buffers are unable to maintain pH, presumably due to acidic or alkaline components of PM, requiring an optimum concentration (5mM in this study) of acetate and formate for Fe solubility measurements. Similar extraction procedures revealed that oxalate buffer inhibits the formation of Fe(II)–ferrozine complex, especially with Fe(III)-containing solutions, rendering it unsuitable for Fe solubility measurements by Ferrozine method. Application of the optimized analytical method to PM samples from different environments showed quite variable Fe solubility, with the lowest (<1%) in dust-impacted samples and the highest (5%) in urban samples. The highest solubility (6.8%) was observed in ambient PM2.5 samples influenced by anthropogenic sources (car emissions) with more than 90% of soluble Fe in the form of Fe(II). Results from this study highlight the importance of the type and strength of buffer at a given pH for Fe solubility and provide further evidence of a higher Fe solubility in urban PM samples compared to desert dust.
Highlights ► We discuss the effect of extracting buffer solutions on iron solubility and speciation. ► A robust extraction method is proposed and applied to a variety of atmospheric environments. ► Results show a variable but low (<10%) iron solubility. ► Most soluble iron was under the form of iron (II).
Solubility and speciation of atmospheric iron in buffer systems simulating cloud conditions
Abstract The solubility of iron (Fe) in atmospheric particulate matter (PM) is important to understand its chemistry and potential bioavailability to ocean phytoplankton. However, current studies on Fe solubility and its speciation are highly uncertain partly due to inconsistencies in analytical protocols. In this study, cloud-processing of atmospheric PM was simulated in acetate, formate, and oxalate buffers (pH=4.30±0.05) at 0.5, 1, 5, and 20mM. Colorimetric analysis of Fe(II)–ferrozine complex showed that Fe solubility increased by an order of magnitude when acetate and formate concentrations increased from 0.5mM to 5mM, with a higher fraction of soluble Fe in acetate than in formate at lower buffer concentration (0.5mM). Measured pH of sample extracts revealed that weak buffers are unable to maintain pH, presumably due to acidic or alkaline components of PM, requiring an optimum concentration (5mM in this study) of acetate and formate for Fe solubility measurements. Similar extraction procedures revealed that oxalate buffer inhibits the formation of Fe(II)–ferrozine complex, especially with Fe(III)-containing solutions, rendering it unsuitable for Fe solubility measurements by Ferrozine method. Application of the optimized analytical method to PM samples from different environments showed quite variable Fe solubility, with the lowest (<1%) in dust-impacted samples and the highest (5%) in urban samples. The highest solubility (6.8%) was observed in ambient PM2.5 samples influenced by anthropogenic sources (car emissions) with more than 90% of soluble Fe in the form of Fe(II). Results from this study highlight the importance of the type and strength of buffer at a given pH for Fe solubility and provide further evidence of a higher Fe solubility in urban PM samples compared to desert dust.
Highlights ► We discuss the effect of extracting buffer solutions on iron solubility and speciation. ► A robust extraction method is proposed and applied to a variety of atmospheric environments. ► Results show a variable but low (<10%) iron solubility. ► Most soluble iron was under the form of iron (II).
Solubility and speciation of atmospheric iron in buffer systems simulating cloud conditions
Upadhyay, Nabin (author) / Majestic, Brian J. (author) / Herckes, Pierre (author)
Atmospheric Environment ; 45 ; 1858-1866
2011-01-05
9 pages
Article (Journal)
Electronic Resource
English
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