Measurements of ultrafine particles carrying different number of charges in on- and near-freeway environments

• Published in: Atmospheric environment (1994) 2012-12, Vol.60, p.564-572
• Main Authors: Lee, Eon S., Xu, Bin, Zhu, Yifang
• Format: Article
• Language: English
• Subjects: Analog computers; Applied sciences; atmospheric chemistry; Atmospheric pollution; Charge; Charged particles; Decay; Decay rate; Diesel; Diesel fuels; electrical charges; Exact sciences and technology; Freeway; Freeways; highways; Nucleation; particles; Pollutants physicochemistry study: properties, effects, reactions, transport and distribution; Pollution; Ultrafine particle
• ISSN: 1352-2310; 1873-2844
• DOI: 10.1016/j.atmosenv.2012.06.085

This paper presents measurements of electrical charges on ultrafine particles (UFPs) of different electrical mobility diameters (30, 50, 80, and 100 nm) in on- and near-freeway environments. Using a tandem Differential Mobility Analyzer (DMA) system, we first examined the fraction of UFPs carrying different number of charges on two distinctive freeways: a gasoline-vehicle dominated freeway (I-405) and a heavy-duty diesel truck dominated freeway (I-710). The fractions of UFPs of a given size carrying one or more charges were significantly higher on the freeways than in the background. The background UFPs only carried up to two charges but freeway UFPs could have up to three charges. The total fraction of charged particles was higher on the I-710 than I-405 across the studied electrical mobility diameters. Near the I-405 freeway, we observed a strong decay of charged particles on the downwind side of the freeway. We also found fractional decay of the charged particles was faster than total particle number concentrations, but slower than total ion concentrations downwind from the freeway I-405. Among charged particles, the highest decay rate was observed for particles carrying three charges. Near the I-710 freeway, we found strong net positive charges on nucleation mode particles, suggesting that UFPs were not at steady-state charge equilibrium near freeways. ► Electrical charges on ultrafine particles (UFPs) were measured on- and near-freeways. ► The fractions of charged UFPs were significantly higher on the freeways than in the background. ► Charged particles decayed faster than total particles but slower than ion downwind from the freeway. ► Strong net positive charges were found on nucleation mode particles near freeways.