On 3/29/04 7:31 AM, "Bruce Gaarder" <[EMAIL PROTECTED]> wrote: > He says that he generates one pound of CO2 for every mile he drives. Quite > an accomplishment. I'm sure that some chemist can supply a calculation, > but if a gallon of gas weighs six pounds or so, how do you get one pound > of CO2 per mile? Oh, I see, his car only gets one mile per gallon?
Someone asked for a chemist? I'll try to explain this so that chemistry-phobes can follow along. The key issue here is the reaction for the combustion of gasoline, which is mostly heptane (C7H16). C7H16 + 11O2 = 7CO2 + 8H2O In other words, burning one molecule of heptane produces seven molecules of carbon dioxide (CO2) Carbon has an atomic weight of 12, oxygen's is 16, and hydrogen's is 1. So heptane has a molecular weight of 100 (7*12+16*1) and carbon dioxide has a molecular weight of 44 (12+2*16) and the seven molecules of CO2 that come from burning one molecule of heptane have a molecular weight of 308. Thus 1 pound of C7H16 produces 3.08 pounds of CO2. As Bruce correctly points out, 1 gallon of gasoline weighs about 6-7 pounds. So assume 6.5 pounds and multiply that by 3.08 to determine the amount of CO2 produced and you get 20.02 pounds of CO2 per gallon of gas burned. Assuming the average vehicle gets 20 miles per gallon and the result then is 1 pound per mile traveled. In other words, Sean is right. > He says that our air quality is calling for a rapid move away from single > occupancy vehicles. Let's take a quick look at the federal standards and > what the emissions were for typical cars before 1968. These are in grams > per mile and are not related to gallons per mile. It's worth noting that > the standards have required maintaining this performance for the first > 100,000 vehicle miles. > > Type pre-1968 2004 > > Hydrocarbons 10.6 0.125 > CO 84.0 1.7 > NOx 4.1 0.2 > > This is from a 2000 National Academy of Sciences article. There was a > proposed change to the standard aimed at ozone, which is the main problem > now, which would have a fleet average. This change would cut NOx to 0.07, > HC to about 0.09, and CO to about 4.2. It's debatable whether our air quality is better or worse now than 1968 because we know a lot more now than we did then about air quality and our definition of "good" air quality has changed - unless you're a member of the Bush Administration, that is. Bruce is certainly correct that federal emissions standards have improved for individual motor vehicles since 1968. What he overlooks, however, is that vehicle miles traveled per person have risen dramatically, even accounting for population growth and average fuel economy has been declining as of late. Unlike the chemicals cited by Bruce, CO2 emissions (Sean's main concern) are strongly related to fuel economy. I cannot draw direct comparisons between Bruce's use of 1968 and 2004, but I can cite some facts from the 2001 MPCA legislative report, "Air Quality in Minnesota: Problems and Approaches," to back up my assertion: http://www.pca.state.mn.us/hot/legislature/reports/2001/airquality.html "According to the Metropolitan Council's 1990 Travel Behavior Inventory report, from 1970 to 1990, the population of the Twin Cities seven-county area increased by 20% but daily vehicle-miles traveled (VMT) increased by 130%." "Since 1988, there has been an overall decline in light vehicle fuel economy. The average fuel economy for all model year 2000 light vehicles is now 24.0 miles per gallon and is as low as it has been at any time since 1980. Average light vehicle fuel economy is now 7% lower than 1987 and 1988." "Sales of light trucks, which include sport utility vehicles (SUVs) vans and pickup trucks, have risen steadily for over 20 years and now make up 46% of the U.S. light vehicle market - more than twice their market share as recently as 1983." The statements I'm citing come from Appendix I: Mobile Source Emissions and Trends Mark Snyder Windom Park B.S. Chemistry University of Minnesota - class of 1997 REMINDERS: 1. Think a member has violated the rules? Email the list manager at [EMAIL PROTECTED] before continuing it on the list. 2. Don't feed the troll! Ignore obvious flame-bait. For state and national discussions see: http://e-democracy.org/discuss.html For external forums, see: http://e-democracy.org/mninteract ________________________________ Minneapolis Issues Forum - A City-focused Civic Discussion - Mn E-Democracy Post messages to: mailto:[EMAIL PROTECTED] Subscribe, Un-subscribe, etc. at: http://e-democracy.org/mpls
