When a cars engine runs it reacts N2 and O2 during combustion under high heat creating NO as a by product. NO is a harmful chemical to be released into the air because it can undergo further chemical reactions leading to NO2. Together, NO and NO2 are referred to as NOx. These chemicals are important because they are involved in numerous photochemical reactions that lead to the creation of low altitude ozone O3, which is a primary component of smog. NOx can also react to create acid rain. According to the EPA (2003), vehicles contributed to 55 % of the total man made source of NOX emissions (http://www.epa.gov/air/urbanair/nox/index.html). We all drive cars, so each of us has a level of responsibility in creation of smog and acid rain; it is important to us to understand just how much Nox is being released by our cars.
Particulate matter is also created by the engines mechanical processes and released in emissions. Particulates also contribute to smog and therefore contribute to health problems correlated with this phenomenon. Some studies have even correlated increased levels of smog to death rate (Baird and Cann, 2005). The sizes of particles are important because the small, man made particles are inhaled directly into lungs; our bodies are not adapted to processing or filtering them or otherwise protecting us. Larger particles can be trapped by our bodies, and are less harmful to the environment because they do not stay in the air as long before settling out. The size and the amount of particulate matter that is released by our vehicles was also a focus of the study.
In order to investigate these two common pollutants from car emissions we conducted an experiment to identify the concentration of NOx and the size and concentration of particulate matter in seven different car models. The cars that were tested ranged in age from 1979 to 2001 and included small models such as a Corolla and Jetta. The NOx was tested by collecting air samples directly from the tail pipe of the running cars. Air samples were mixed with an NO absorbing solution that then reacted to give us a measurable amount of color. A UV vis-spectrophotometer was used to measure this difference in color. By creating a set of standard solutions with known concentrations that were measured by the UV vis- spectrophotometer a calibration curve was calculated. The concentration of the NOx in the car emissions could then be visually compared to the standard solutions and a concentration was calculated in units of parts per million (ppm). This tells us how many particles of NOx there are in relation to all the particles in the air. The particulate matter was measured separately using a Scanning Mobility Particle Sizing (SMPS) device. This device calculates the concentration and size of particulate matter using several pieces of machinery and a computer.
Figure 1 illustrates NOx concentration data from four of the cars that were tested. We observed that total NOx generally starts out at a relatively high range, and decreases for most cars after warm-up. This trend likely results from the fact that all cars that we tested use catalytic converters designed to reduce emissions, which do not begin to work until the cars are warm. Newer cars were built under emission regulations that have become increasingly more stringent. This is supported by the data that showed overall NOx was the highest in older vehicles and the lowest in newer vehicles.
The data from Scanning Mobility Particle Sizing (SMPS) system of the 2001 Jetta and the 1979 Corolla (Figure 2) show the amount of particles at the range of sizes from 0-1000 nm in diameter. The important thing to notice is that for the Corolla the majority of particles are released before the car has warmed up and before the catalytic converter starts to work. For the Jetta the opposite is true, the majority of the particles are released after the car has warmed up. The sizes of the particles are slightly smaller also in the Jetta than the 100 nm particles released during the cold start of the Corolla. The regulation of large particulate matter in the newer Jetta might be allowing for the smaller particles to be released and go less noticed.
All of the data helps us to make observations about the composition of car emissions and connect it directly to creation of air pollution. As the world continues to modernize man made pollutants are becoming more noticeable and problematic. Specifically, increased vehicle emissions of NOX and particulates are polluting most moderately sized cities. Understanding how cars release these harmful pollutants increases our awareness of the issue and hopefully will help us to create future solutions
No comments:
Post a Comment