Ok, here's some numbers.
The United States emits 5.7 billion tons of CO2 per year. The next closest is China at 3.4 billion, however that is less than 20 tons per person, per year. Compare this to Qatar, the UAE, and Kuwait which each emit more than twice that number. In terms of efficiency, we're running in the middle of the pack. China beats us, as does Russia.
As for Nitrogen Oxides, our emissions (1,200 tons per sq. mi of densly populated area) are below that of Japan (1,500), the UK (1,700). The UAE again hits near the top of the list with nearly three times that of Japan.
Oh, and the wonderful Sulfur Oxide. The United States produces about 70 kilos per capita per year. Australia is at just over 100, Canada at 90. Right below us is Hungary at ~68. As for SO2, we're practically at the bottom of the international dogpile here with 1700 tons per sq mi of populated area. Belgium dishes out 20,000. The UK is at around 5000. China comes in below them at around 3000.
Regarding urban areas... wow! You've been to Houston? Big deal. Go check out Mexico City sometime. Or Tokyo. Anyway, Mexico City has roughly twice the concentration of NO2 that our worst cities have (130mg per cubic meter vs our 60mg). Italy is way up there as well at 120mg, followed by the UAE (again... 95mg), China (76mg), the UK (65mg). Even Rwanda beats us at our own emissions game here (62mg).
Lets also take a look at CFC and the Ozone Depletion Potential. Remember those? Yeah, its the reason my grandmother stopped using aerosol hairsprays. China and South Korea both produce roughly a thousand times what the US does, each.
Cars! Here we go! The US has the most? Right? Of course we do! We have a huge population and a strong economy. However, we don't have the most cars per capita. The US has about 478 cars per thousand people. Italy's number one at 539. Austria's got 495. The UK is down there at 373. Canada is 460. But it's not just cars that pollute. All motor vehicles do. This includes boats and trains and trucks and motorcycles. We top this list at 765 per thousand people. The next closest major nation is Australia at 619. Despite this, the United States has a surprisingly low number of motor vehicles per square kilometer of populated area, about 47. Japan buries our sorry pedestrian asses with 190. Germany, Italy, Belgium, Iceland, South Korea, the Netherlands, the UK... they all have more than a hundred.
As for automobile emissions, the United States has this wonderful organization called the EPA. They like to rain on our parade every time someone comes out with a new 500hp supercar concept.
Another thing to look at, considering emissions and air pollution, is fossile-fuel consumption. First, coal. The US is number two in the world. China is number one. I should also mention that China is planning to build ~560 new coal plants by 2020. This will reverse the effects of the Kyoto by nearly five times over. Oh well. We tried, right?
The US does top the charts for Natural Gas (with nearly twice the consumption of the number two nation, Russia), and more NG plants are in the works here, as more coal plants are decomissioned. We also are the top user of Nuclear energy. France is right behind us
The US consumes 4 times as much oil per year as the runner-up (Japan). 19.7 million barrels a day, compared to 5.1 million.
Oh and the United States is spending 1.6% of it's GDP on pollution control. This is more than every european country combined. The only country spending more (as a percentage of GDP) is the Netherlands. We spend more money controlling our emissions and pollution than anyone in the world.
Edit: Oh, and I love how everyone is like "Bush didn't join Kyoto" as if it was only him that snubbed it. The Senate turned it down something like 95-0 in 1997. It was turned down again recently. The decision has never been up to Bush.
"Stable and Go". New jobs will be created! 
