[Determination Method and Characteristics of Particle Size Multiplier of PM_2.5 in Road Dust]

The particle size multiplier is a valuable parameter for depicting the particle size distribution characteristics of road dust and calculating road dust emissions. In order to realize the localization of the particle size multiplier, the AP-42 and TRAKER methods were used for sampling on typical and different types of roads in Baoding in March 2019. Then, the particle size multiplier of road dust PM_2.5 (K_2.5) was calculated using the correction formula, and the characteristics were analyzed. The results indicated:① The K_2.5 obtained separately by AP-42 and TRAKER were 0.21 g·VKT^-1 and 0.23 g·VKT^-1 on average, which correlated well, with a high correlation coefficient of 0.6. The PM_2.5 emission factors calculated using the K_2.5 of the different methods were almost at the same value, indicating that TRAKER method based on a laser sensor could measure and calculate the K_2.5 and could be directly used to obtain the particle size multiplier or be converted using the fitting equation. ② The characteristics of the K_2.5 in Baoding were ranked as:ExpresswayK_2.5 characteristics demonstrated that the average K_2.5 was higher than 0.15 g·VKT^-1 (the value recommended by US EPA) in Baoding City, which would cause an underestimate of road dust emissions and increase the uncertainty of the emissions inventory if the recommended value from the EPA were adopted. The K_2.5 in Baoding City is relatively high, indicating that the road dust contains a significant number of micro particles, increasing the contribution of road dust to urban atmospheric PM_2.5.