Impact of temperature dependence on the possible contribution of organics to new particle formation in the atmosphere

Other literature type English OPEN
Yu, Fangqun ; Luo, Gan ; Nadykto, Alexey B. ; Herb, Jason (2016)

Secondary particles formed via new particle formation (NPF) dominate cloud condensation nuclei (CCN) abundance in most parts of the troposphere and are important for aerosol indirect radiative forcing (IRF). Laboratory measurements have shown that certain organic compounds can significantly enhance binary nucleation of sulfuric acid and H<sub>2</sub>O. According to our recent study comparing particle size distributions measured in nine forest areas in North America with those predicted by a global size-resolved aerosol model, current H<sub>2</sub>SO<sub>4</sub>-Organics nucleation parameterizations appear to significantly over-predict NPF and particle number concentrations in summer. The lack of the temperature dependence in the current H<sub>2</sub>SO<sub>4</sub>-Organics nucleation parameterization has been suggested to be a possible reason for the observed over-prediction. In this work, H<sub>2</sub>SO<sub>4</sub>-Organics clustering thermodynamics from quantum-chemical studies has been employed to develop a scheme to incorporate temperature dependence into H<sub>2</sub>SO<sub>4</sub>-Organics nucleation parameterization. We show that temperature has a strong impact on H<sub>2</sub>SO<sub>4</sub>-Organics nucleation rates, and may reduce nucleation rate by ~ one order of magnitude per 10&thinsp;K of the temperature increase. The particle number concentrations in summer over North America based on the revised scheme is a factor of more than two lower, in much better agreement with the observations. With the temperature-dependent H<sub>2</sub>SO<sub>4</sub>-Organics nucleation parameterization, the summer month CCN concentrations in the lower troposphere in the northern hemisphere are about 10&ndash;30&thinsp;% lower and the aerosol first IRF about 0.5&ndash;1.0&thinsp;W/m<sup>2</sup> less negative compared to the temperature independent one. This study highlights the importance of the temperature effect and its impacts on NPF in global modeling of aerosol IRF.
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