Indirect method for determining the dry deposition velocity of submicron particulate matter on leaves

Abstract

Plant leaves, as natural receptors of airborne particles, can retain particles onto their surfaces, and absorb gaseous pollutants, thus mitigating air pollution and improving air quality. Dry deposition is considered the main process for particle removal from the atmosphere, and its velocity (Vd) is a crucial parameter for describing the process. Wind tunnels, a conventional approach to determine Vd, are costly and require substantial space, and regular inspections to maintain their systematic integrity. Hence, this study established a simpler and more straightforward method based on relevant research to obtain the submicron particulate matter (aerodynamic diameter ≤1 μm; PM1) Vd on plant leaves. This method involves determining the attenuation pattern of particle concentration in a smog chamber. The Vd values of six tree species (three broadleaved and three coniferous) were obtained through the indirect method. In addition, we determined the Vd of the same tree species with a wind tunnel and compared the values from both methods. Through the paired-samples t-test, it's found that there is no significant difference (sig. = 0.59) between these two methods, which means that the indirect method is feasible to determine Vd. We also compared our results with those from other researches, and we found that the Vd values in our study might be lower because leaves and shoots were used in this research, while branches or seedings were selected in the literature. Overall, when applying such values to predictive models or in concrete studies, researchers must consider factors such as real-time meteorological conditions (humidity, temperature, etc.) and pollutant concentration. The indirect method requires less space and is less costly than the wind tunnel method; therefore, it can easily be used to conduct experiments under controlled conditions, which is helpful for simulating various scenarios.