Connection of organics to atmospheric new particle formation and growth at an urban site of Beijing

In the present work, we aim to elucidate the roles of low-volatility organic vapors in atmospheric new particle formation in urban Beijing. Proposed organic molecules are derived from both the ambient measurement and the reasonable proxy. Several representations for the nucleation theories involving sulfuric acid and organic vapors are evaluated. The particle nucleation rates show good correlations both with sulfuric acid and organic vapors, suggesting that both play an important role in the atmospheric new particle formation. For the entire data set, the best fit (R = 0.79, slope = 1.1) between the observed and modeled particle nucleation rates is achieved with the homogenous nucleation theory of sulfuric acid (both homomolecularly and heteromolecularly) with separate coefficients in J = KSA1[H2SO4]2 + KSA2[H2SO4][Org]. In addition, sulfuric acid concentration only contributes a small fraction (<15%) to the total observed growth rate. The growth rates of 7–30 nm particles show positive correlation with the organic vapors oxidized by ozone, suggesting that particle nucleation may be controlled by the light intensity or OH concentration, while the growth of nucleation mode particles seems to be limited more by the concentrations of the organic precursors.