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 20. mM. Colorimetric analysis of Fe(II)-ferrozine complex showed that Fe solubility increased by an order of magnitude when acetate and formate concentrations increased from 0.5. mM to 5. mM, with a higher fraction of soluble Fe in acetate than in formate at lower buffer concentration (0.5. mM). 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 (5. mM 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.
Original language | English (US) |
---|---|
Pages (from-to) | 1858-1866 |
Number of pages | 9 |
Journal | Atmospheric Environment |
Volume | 45 |
Issue number | 10 |
DOIs | |
State | Published - Mar 2011 |
Keywords
- Buffer solution
- Clouds
- Iron solubility
- Particulate matter
- Soluble iron
- Speciation
ASJC Scopus subject areas
- General Environmental Science
- Atmospheric Science