PM2.5 is lethal and one of the largest causes of heart disease and cancer. It is proven that if you live within about 1/2 mile of an interstate you are over 300% more likely to develop a leukemia. When this fine soot/auto exhaust containing 100's of toxins like benzene and mercury are at high levels the concentrations can be over 110,000 nanometer sized particles per cubic centimeter of air. It is measurable withing the bloodstream within an hour of exposure. For every doubling of the pm2.5 level the heart attack hospital admission rate goes up significantly. Personally it has caused headaches, blurred vision and knumb feet. Just compare the US maps of pm2.5 to those of US heart disease and cancer rates at www.blueskiesnow.blogspot.com DRIVE A HYBRID !! and get over a 97% reduction in emmissions. You don't plug them in !! 55 mpg in city and NZEV status (near zero emmissions vehicle).