Inhibition of New Particle Formation (NPF) in an Experimental Fores: Effect of NOx in a Biogenic Environment

Abstract:

In this study, the underlying mechanisms of the repression of new particle formation (NPF) in an experimental forest in central Taiwan (23.92 °N, 120.77 °E) during the spring (March) of 2014 were investigated. During the intensive observation period, only a single episode of NPF was detected even with suitable conditions (i.e. sulfur dioxide levels and condensation sink) in most of the sampling dates. To account for the cause of the infrequent particle formation, parameters such as meteorological conditions, OH radical scavenging of isoprene and the effect of NOx pollutant were explored in this study. Among the stated parameters, only the effect of NOx, which was expressed as the proportion of monoterpene and NOx mixing ratio (MT/NOx), showed a significant difference between the NPF (2.138 ppbC/ppb) and the non-NPF (0.8584 ppbC/ppb) events. Based on the backward trajectory analysis, the elevated NOx concentration measured in the experimental forest was possibly transported from urban areas with large emissions of inorganic contaminants. Our results underscore a potential link between anthropogenic activities and aerosol nucleation processes, which in turn can change the global budget of aerosol and its contribution to radiative forcing.