How aging process changes characteristics of vehicle emissions? A review

Abstract

With increasing road and non-road vehicles in use, air quality and human health have been under greater pressure in recent years. Generally, changes involving aerosol-based vehicular pollutants are aging processes, which can alter vehicle emissions to varying degrees. We summarize the effects of the aging process on vehicle emission characteristics in this review. The initial statuses of the hygroscopicity, size distribution, phase partitioning, morphology, and chemical composition of vehicle emissions are described. Changes in these properties are produced by a series of actions, including physical means and photochemical reactions, which are characterized by the organic aerosol (OA) atomic ratio and mass spectra. Moreover, the vehicle driving cycle, after-treatment technologies and fuels affect these properties in various ways. The key driving forces of the aging mechanism of vehicle emissions mainly include diffusion, phase partitioning, and organic gas oxidation. Future research requirements to support vehicle-related air pollution control are also discussed, involving topics such as cloud condensation nuclei (CCN) and ice nucleation (IN) of aged diesel particles, reacting phases, unknown precursors or formation pathways, aged OA and source appointment, and emission controls. To what degree the aging process changes vehicle emission properties needs further study.

Keywords:

• Aging process
• chemical properties
• physical properties
• vehicle emissions

Conflict of interest

The authors declare no competing financial interest.

Additional information

Funding

This work was supported by National Key R&D Program under Grant [2016YFC0201504], Excellent Young Scholars under Grant [41822505], the National Research Program for Key Issues in Air Pollution Control under Grant [DQGG0201&0207], the National Natural Science Found of China under Grant [91544110 and 41571447], Beijing Nova Program under Grant [Z181100006218077], Special Fund of State Key Joint Laboratory of Environment Simulation and Pollution Control under Grant [16Y02ESPCT], and National Program on Key Basic Research Project under Grant [2014CB441301].