Oxidative Potential and Chemical Characteristics of Ambient PM2.5 in Guangzhou, China
<p>The dithiothreitol (DTT) assay is widely used to characterize the Oxidation Potential (OP) of atmospheric particulate matter (PM), which can cause adverse effects on human health. However, it&#8217;s under debate which chemical species determines the consumption rate of DTT. During January and April 2018, we measured the improved DTT assay of daily PM<sub>2.5</sub> samples collected in Guangzhou, China with complimentary measurements of water-soluble ions, organic/elemental carbon (OC/EC) and metal elements. The average sampled air volume normalized consumption rate of DTT (DTT<sub>v</sub>) was 4.67 &#177;1.06 and 4.45 &#177; 1.02 nmol min<sup>-1</sup> m<sup>-3</sup>, in January and April, respectively while the average PM<sub>2.5</sub> mass normalized consumption rate of DTT (DTT<sub>m</sub>) was 13.47 &#177; 3.86 and 14.66 &#177; 4.49 pmol min<sup>-1</sup> &#956;g<sup>-1</sup>. Good correlations were found between DTT<sub>v</sub> and concentration of PM<sub>2.5</sub>, OC, and EC while no correlation was found between DTT<sub>m</sub> and concentrations of water-soluble ions, OC, EC or metal element, which is consistent with most early observations. We also evaluated the contribution of soluble metals to DTT assay by addition of EDTA, a strong metal chelator. We found that nearly 90% of DTT<sub>v</sub> and DTT<sub>m</sub> were reduced by EDTA, suggesting a dominant role of soluble metals in determining the response of DTT to ambient PM<sub>2.5</sub>. Based on responses of DTT to soluble metals in literature, we found that Cu(II) and Mn(II) are the major contributors to OP of PM<sub>2.5</sub> in Guangzhou. The correlation coefficient between DTT<sub>m </sub>and OC shows a clear increase after addition of EDTA, implying that the response of DTT to quinones is not strongly suppressed by EDTA.</p>