Triplet State Formation of Chromophoric Dissolved Organic Matter in Atmospheric Aerosols: Characteristics and Implications

Abstract

<p><strong>Abstract.</strong> There is chromophore dissolved organic matter (CDOM) in the atmosphere, which may form triplet-state chromophoric dissolved organic matter (<sup>3</sup>CDOM*) to further driving the formation of reactive oxygen species (ROS) under solar illumination. <sup>3</sup>CDOM* contributes significantly to aerosol photochemistry and plays an important role in aerosol aging. We quantify the ability to form <sup>3</sup>CDOM* and drive the formation of ROS by primary, secondary and ambient aerosols. Biomass combustion has the strongest <sup>3</sup>CDOM* generation capacity and the weakest vehicle emission capacity. Ambient aerosol has a stronger ability to generate <sup>3</sup>CDOM* in winter than in summer. Most of the triplet states generation conform to first-order reaction, but some of them do not due to the different quenching mechanism. The structural-activity relationship between the CDOM type and the <sup>3</sup>CDOM* formation capacity shows that the two types of CDOM identified, which similar to the nitrogen-containing chromophores contributed 88 % to the formation of <sup>3</sup>CDOM*. The estimated formation rate of <sup>3</sup>CDOM* can reach ~ 100 μmol m<sup>−3</sup> h<sup>−1</sup> in the atmosphere in Xi'an, China, which is approximately one hundred thousand-times the hydroxyl radical (•OH) production. This study verified that <sup>3</sup>CDOM* drives at least 30 % of the singlet oxygen (<sup>1</sup>O<sub>2</sub>) and 31 % of the •OH formed by aerosols using the spin trapping and electron paramagnetic resonance technique.</p>