There is currently much concern over particles suspended in the ambient air, their effects on people and the environment throughout the world. The suspended particles can cause adverse health effects, reduce visibility and over the course of time wear buildings. Primary air quality concerns are of particles, their effects and their key characteristics. Particle number concentration (NC) of traffic emissions is an important element of the study, specifically heavy duty diesel engine emissions. Particle number concentration is the number of particles of a specific size in a unit of air; in this study they are measured by the number of particles of a specific size range per cubic centimeter (#/cc). Particulate matter (PM) are microscopic pieces of matter that can be formed in the atmosphere or emitted by a source, and can be characterized by their diameter size range. Fine particulate matter are particles of diameters 2.5 μm or smaller and Ultra Fine (UF) PM are particles of 0.1 μm and smaller.
The current regulated PM 2.5 particles are the mass concentration (MC) of those with a fifty percent cutoff diameter at 2.5 μm. The regulation for PM does not evaluate the size range of the particles or their quantitative number count. The size of the particle is important in that it determines it's potential to travel through the respiratory system. As there are many studies that measure particulate matter and determine the important affecting characteristics, there are also concerns of the PM from diesel emissions and their impacts. Diesel fuel and gasoline are both usually created from petroleum, although gasoline is more refined (World Book Inc., 2005). Vehicular emissions have been studied for many years and it's important that distinctions are made between gasoline and diesel emissions. This study compares the mass and number concentrations of diesel emissions to a prior study of gasoline emissions done at The University of Texas at El Paso. The purpose of the study is to characterize the particles' mass and number concentrations, as well as to distinguish diesel particulate emissions from gasoline (petrol) particulate emissions at a truck stop.
The study took place outside an IdleAire office located in a Petro truck stop parking lot. The Petro truck stop is located in El Paso, Texas along the Interstate Highway 10 corridor. Mass concentrations of PM 2.5 and PM 10 along with particle number concentrations of over 190 particle size ranges were measured. The number concentration and mass concentration of particles from 0.3 μm to 20 μm were measured by the Aerodynamic Particle Sizer spectrometer (APS), Model 3321 of TSI. Number concentrations of diameters from 5.94 nm to 225 nm were measured by the Scanning Mobility Particle Sizer (SMPS), TSI (SMPS) Model 3936, with a 0.70 μm impactor that discards the larger particles. The mass concentrations of PM 2.5 and PM 10 were measured by two Tapered Element Oscillating Microbalances (TEOM series 1400a, Rupprecht & Patashnick Co. Inc.). All instruments were collocated outside the IdleAire office and placed in a designated shelter to protect the instruments from excessive heat and moisture.
This study found that the plateaus and peaks in the diurnal mass concentration graphs did not adequately represent the number concentration trend unless there was an abundance of ultra-fine particles identified. Size distribution graphs show the majority of these particles to be in the ultra-fine size range between 0.01 μm and 0.06 μm which are much finer than the PM 2.5 regulations. When graphs were compared to a UTEP study, Investigation of the Nocturnal PM Peaks for Evidence for Association with Population Health: Diurnal Variations in Ambient Fine and Ultrafine Particles Concentrations in El Paso, Texas by Jessica Gamez which was assessed in a gasoline dominant parking area, the Petro emissions showed up to ten times more particle concentration, especially in the ultra-fine range. Therefore, it is evident that mass concentrations measurements are not equivalent to number concentrations, omitting vital information as to what's in the atmosphere. This is proven by the divergent mass and number concentration graphs that are only remotely comparable during extremely large amounts of suspended particulates. The study consequently illustrated the mass concentrations to represent a different and less accurate result than number concentrations. The study shows diesel engines to emit significantly more ultra-fine particles than gasoline engines, proving their emissions to be more detrimental to our health and increasing the vulnerability to exposure.
