A sampling and measurement system for motorcycle exhaust PM2.5
Date Issued
2015
Date
2015
Author(s)
Lai, Ji-Ying
Abstract
Motorcycle was an important transportation tool in tropical and subtropical countries. It becomes even more popular nowadays because of convenience, mobility and economy. In 2014, Taiwan had more than 14 million motorcycles, accounting for 64.7% of all motor vehicles. Many studies have been conducted to measure the quantity of regulated air pollutants such as CO, HC and NOx from motorcycles .In addition to these regulated air pollutants, the unregulated constituents can be significant because of particulate matter formation in urban areas and their potential health effects on human. Hence, the main objective of the present study was to develop a sampling and measurement system for PM2.5 emission from motorcycles. The sampling and measurement system was designed to include a chamber adapter connecting to tailpipe, a dehumidifying unit, an aerosol size-selective device, and an appropriate measurement instrument. The test particles were generated by using a 125 cc four-stroke engine controlled by a dynamometer. The particle size distribution, hygroscopic properties, and water content of emissions were evaluated before choosing the particle separator and dehumidifier. The effects of temperature, humidity, condition time on the filter weighting were evaluated. The particle penetration of VPR in different temperature were measured by SMPS. Several real-time aerosol instruments (SMPS, FMPS, CPC, AE51) were employed to measure the aerosol number concentration and/or size distribution, mass concentration, or black carbon. These measurements were then compared with the mass of filter samplers. The results indicated that the engine emission at idle mode (1750 rpm) had a CMD of 0.05 μm, GSD of 1.8, and number concentration of 104~105 #/cm3. The particles generated from motorcycle engine did not growth even if the RH was up to 100 %. Hence, the purpose of dilution was to decrease the sample temperature and avoid the water condensed on the sampling line. The sample water content was ranging from 7 % to 10 %, depending on the speed. Therefore, the dilution ratio of 10 was sufficient to avoid water condensation, but the drawback was the resultant low particle concentration. The Nafion dryer had almost no particle loss for particles from 30 to 750 nm, and had excellent dehumidifying efficiency, but it was expensive. The ice bath was cheap and simple to operate. It efficiently decreased the temperature and humidity of the motorcycle exhaust. The cyclones showed the same separation efficiency curve with the US EPA PM2.5 sampling convention. The results indicated that the PTFE filter was the most appropriate media for sampling particulate matter. The mass decrease due to semi-volatile matter decreased with increasing temperature of the sampling filter holder. The VPR reduced the particle size and resulted in the underestimation of particle number concentration, probably due to some of the particles smaller than 2.5 nm, the lower detection limit of ultrafine condensation particle counter. The aerosol emission measurements from motorcycles indicated that the particle mode was around 50 nm. The mass and number concentrations of carburetor engines were 730.4 μg/m3 and 2×106 #/cm3, respectively. For electronic injection engines, the mass and number concentrations were 139.6 μg/m3 and 1.2×105 #/cm3, respectively. The regression analysis showed that the correlation coefficients of the filtered mass against FMPS, SMPS, CPC and AE51 measurements were 0.761, 0.828, 0.798 and 0.950, respectively. Therefore, the combination of an ice bath, a cyclone, and the black carbon aerosol monitor (AE51) appeared to be most ideal for motorcycle exhaust PM2.5 measurements.
Subjects
Mobile sources
Particulate matter
Type
thesis