Simulation of Gas‐Particle Partitioning of Semi‐Volatile <i>n‐</i>Alkanes and PAHs in Nanjing, China, and Denver, United States: Effects of Vapor Pressure and Surface Adsorption Estimation

Abstract The concentration data of semi‐volatile n‐ alkanes and PAHs in the gas phase and in PM 2.5 were obtained from Nanjing and Denver. First, the gas‐particle partitioning coefficients of the target compounds were calculated and compared with the predictions based on the equilibrium absorptive partitioning theory. Although the vapor pressure ( p o L ) estimation method was selected to improve the agreement between measured and predicted partitioning coefficients, n‐ alkanes in Denver and PAHs in both cities exhibited stronger sorption to PM 2.5 than predicted. By including the adsorption mechanism, the average logarithms and temporal variations of the partitioning coefficients were well simulated in both Nanjing and Denver. The partitioning of n‐ alkanes in Nanjing can be primarily explained by the absorption mechanism, while the adsorption mechanism dominates that for n‐ alkanes in Denver and PAHs in both cities. To obtain an optimal simulation, the p o L of n‐ alkanes and PAHs was estimated using the SPARC and SIMPOL—two group contribution methods, respectively, and the difference between desorption and vaporization enthalpies was set between 2 and 3 kcal mol −1 for n‐ alkanes in Denver and PAHs in both cities. Therefore, the estimation of p o L and surface adsorption should be carefully considered when parameterizing the gas‐particle partitioning of non‐polar organic compounds in future field and modeling studies.