Identifying the sources of nucleation mode particles by analyzing black carbon coating thickness in urban atmospheres

Abstract

Nucleation mode particles (NMPs, less than 25 nm in diameter) are ubiquitous in the atmosphere and have a negative impact on human health and climate. New particle formation (NPF) from extremely low volatile vapors is the dominating source of NMPs globally, but direct emissions from on-road vehicles are also an important source in the urban boundary layer. However, quantifying the contribution of NMPs in the urban boundary layer from NPF and direct emissions is a challenge owing to the complex sourcing and evaluation processes of NMPs. Here, black carbon coating thickness, together with the quantity of a fingerprint organic aerosol marker related to on-road vehicle emissions (HOA, hydrocarbon-like organic aerosol), was utilized to distinguish and determine the two main sources of NMPs. Owing to the constrains of this approach, the influence of upward wind on NMP transportation was excluded. Statistical analysis showed that NPF was the dominant source of NMPs under NPF, non-NPF, and haze conditions, whereas direct vehicle emissions remained a relatively constant contributor.