Brake wear-derived particles:Single-particle mass spectral signatures and real-world emissions

Brake wear is an important but unregulated vehicle-related source of atmospheric particulate matter(PM).The single-particle spectral fingerprints of brake wear particles(BWPs)provide essential information for understanding their formation mechanism and atmospheric contributions.Herein,we obtained the single-particle mass spectra of BWPs by combining a brake dynamometer with an online single particle aerosol mass spectrometer and quantified real-world BWP emissions through a tunnel observation in Tianjin,China.The pure BWPs mainly include three distinct types of particles,namely,Bacontaining particles,mineral particles,and carbon-containing particles,accounting for 44.2%,43.4%,and 10.3%of the total BWP number concentration,respectively.The diversified mass spectra indicate complex BWP formation pathways,such as mechanical,phase transition,and chemical processes.Notably,the mass spectra of Ba-containing particles are unique,which allows them to serve as an excellent indicator for estimating ambient BWP concentrations.By evaluating this indicator,we find that approximately 4.0%of the PM in the tunnel could be attributable to brake wear;the real-world fleet-average emission factor of 0.28 mg km
1 veh
1 is consistent with the estimation obtained using the receptor model.The results presented herein can be used to inform assessments of the environmental and health impacts of BWPs to formulate effective emissions control policies.

Effect of cOVID-19 lockdown on the characterization and mixing state of carbonaceous particles in the urban atmosphere of Liaocheng, the North China Plain

To investigate the effect of covID-19 control measures on aerosol chemistry,the chemical compositions,mixing states,and formation mechanisms of carbonaceous particles in the urban atmosphere of Liao-cheng in the North China Plain(NCP)were compared before and during the pandemic using a single particle aerosol mass spectrometry(SPAMS).The results showed that the concentrations of five air pollutants including PM2.5,PM1o,SO2,NO2,and cO decreased by 41.2%-71.5%during the pandemic compared to those before the pandemic,whereas O3 increased by 1.3 times during the pandemic because of the depressed titration of O3 and more favorable meteorological conditions.The count and percentage contribution of carbonaceous particles in the total detected particles were lower during the pandemic than those before the pandemic.The carbonaceous particles were dominated by elemental and organic carbon(ECOC,35.9%),followed by elemental carbon-aged(EC-aged,19.6%)and organic carbon-fresh(OC-fresh,13.5%)before the pandemic,while EC-aged(25.3%),ECOC(17.9%),and secondary ions-rich(SEC,17.8%)became the predominant species during the pandemic.The carbonaceous particle sizes during the pandemic showed a broader distribution than that before the pandemic,due to the condensation and coagulation of carbonaceous particles in the aging processes.The relative aerosol acidity(Rra)was smaller before the pandemic than that during the pandemic,indicating the more acidic particle aerosol during the pandemic closely related to the secondary species and relative humidity(RH).More than 95.0%and 86.0%of carbonaceous particles in the whole period were internally mixed with nitrate and sulfate,implying that most of the carbonaceous particles were associated with secondary oxidation during their formation processes.The diurnal variations of oxalate particles and correlation analyses suggested that oxalate particles before the pandemic were derived from aqueous oxidation driven by RH and liquid water content(LwC),while oxalate particles during the pandemic were originated from O3-dominatedphotochemical oxidation.