Hydrogen is not exactly a fuel. That is, we don't burn it to make energy. It's used more as a medium for storing and transporting energy.

The science of hydrogen fuel cell systems is based on a simple concept. When you combine hydrogen with oxygen, energy is released. You get electricity. What makes it such a clean technology is that the byproducts of that chemical reaction are just heat and water.  So when a fuel cell takes hydrogen from a fuel tank and combines it with oxygen in the air, it produces electricity and emits only a wisp of heated water vapor from the tailpipe.

Hydrogen is combustible (remember the Hindenburg?), and needs to be handled carefully. However, there are easy ways to demonstrate electrolysis, which breaks water apart into oxygen and hydrogen, and the opposite process of joining those chemicals. In fact, you could make a type of fuel cell in your kitchen, with a popsicle stick, battery clips, Scotch tape and a few other household products. You do need one item that can't be found in your kitchen: platinum wire or platinum-coated nickel wire.

Hydrogen is the most abundant element in the universe. And hydrogen fuel cell conversion is a squeaky clean technology. But the production of hydrogen for use in fuel cells — that can produce a lot of carbon dioxide. In fact, most hydrogen is currently made by stripping, or re-forming, natural gas. That's one of the ongoing criticisms of fuel-cell technology, that it generates greenhouse gas emissions just to get the hydrogen in the first place.

Fuel cells also can store energy generated by solar-powered electrolysis, as well as similar energy generated by wind and hydropower. That's the kind of hydrogen generation that advocates hope to eventually use in fuel cells. But being able to store energy also makes it extremely attractive to harnessing wind, solar and hydropower.

For example, California could generate a lot of wind energy at night, but since electricity has to be used right away, that nighttime, offpeak energy is less valuable. But if it could be stored in a fuel cell through the electrolysis process, that would make it much more lucrative.

Listen to the Where's my Hydrogen Highway? radio report online, and watch our Web Extra Slideshow.

As this radio story airs, Congress is debating two Cash for Clunkers proposals, one from the Senate and one from the House of Representatives. (A third proposal, also from the Senate, is almost identical to the House version.) Both would pay consumers to scrap their "clunkers" in exchange for brand-new, more fuel-efficient models. Both define "clunker" as a car that gets less than 18 miles per gallon. But after that, they diverge.

The House version comes from Democrats on the House Committee on Energy and Commerce. If it passes, a consumer would get a $3,500 voucher for trading in a truck with 15 miles per gallon in exchange for buying a new truck that gets 16 miles per gallon – a one MPG difference. (If the new truck got 17 miles a gallon, the consumer would earn $4,500). That's why environmentalists complain that the legislation is more about stimulating car sales than it is about getting gas guzzlers off the road.

The Senate version proposed by U.S. Senators Dianne Feinstein (D-Calif.), Susan Collins (R-Maine), and Charles Schumer (D-N.Y.), puts the bar a bit higher. In order to qualify for the $3,500 voucher, that same replacement truck would have to get 20 MPG – five miles per gallon more than the old truck. (An improvement of seven miles per gallon would earn the consumer a $4,500 voucher.)

Interestingly, this is a compromise even for Senator Feinstein herself. Check out her original, more stringent, Cash for Clunkers bill here. Proposed in January, it required stricter efficiency from the replacement vehicle, and would have allowed consumers to use their vouchers for used cars, or for public transit. Those conditions were junked, presumably, because they don't stimulate new car sales.

This article from the Christian Science Monitor, takes the number crunching even farther. Among the details worth considering is the "carbon cost" of making all these new vehicles that consumers will be enouraged to buy, should C4C pass: between 3.5 to 12.4 tons of CO2 per vehicle, according to a Duke economist.

Listen to the Cash for Clunkers radio report online.

You'd have to be a real gas pump aficionado to notice the new gear that gas stations across California are required to have installed by April 1st. California's gas nozzles have been outfitted for some time with vapor-capture devices, designed to cut back on the amount of volatile organic compounds – those smelly fumes – that escape when you pump gas. This explains that accordion-style rubber sheath that bunches up against your gas tank when you pump – a feature you don't necessarily find in states with less stringent air quality laws.

When those fumes combine with sunlight, along with other emissions, they form ground-level ozone, an air pollutant which acts as a greenhouse gas, contributing to global warming much like carbon dioxide does.

Take a look at this nifty, infra-red video footage from the California Air Resources Board, showing how fumes disperse from the gas pump when they aren't properly collected.

Ground-level ozone is also a real problem for human health, especially for people with asthma and respiratory disease. Just this week, UC Berkeley released a study finding that people living in areas with high ozone levels, like Los Angeles and the Central Valley, have a 25-30% greater risk of dying from respiratory disease than those in less ozone-heavy parts of the state, like San Francisco.

By the way, if you're wondering what "ground-level ozone" has to do with that ozone hole we used to hear so much about, here's the short answer: Turns out ozone does different things, depending on where you find it. In the atmosphere, ozone's a good thing. It forms a protective layer that shields the Earth from the sun's radiation – a layer that's been steadily eroded by chlorofluorocarbons, found in aerosol sprays and other places. Here at ground level, ozone's much less likable: a toxic air pollutant, as I said above.

If every station in California installs the new, hi-tech "enhanced vapor recovery system" they'll collectively cut back statewide, ground-level ozone emissions by ten tons a day – that's roughly equivalent to taking 450,000 cars off the road, according to CARB.

Listen to the Changes at the Pump radio report online.

A carbon-tracking cell phone. Credit: Nokia
"Do I get to keep the phone?"

Not exactly the environmentally-conscious line of thinking that organizers were hoping for, but understandable for those high-schoolers holding a brand new, latest version of the Nokia in their hands.

The way the San Francisco pilot program works is like this: students get a mobile phone equipped with a GPS maps application. They fill out a profile with the make and model of the cars they use. The cell phone monitors movement, so it picks up when that student is making a car trip. The server factors in the time of day, the weather and humidity, and the type of car the student is riding in – and then calculates the amount of carbon output that trip represents.

The program currently doesn't differentiate between cars and other forms of transportation – bikes, ferries, trains, carpools, buses – so students may need to note when those trips were not regular car trips. The final number is their carbon rating.

When the program expands to three other San Francisco schools at the end of March 2009, a competition will be formed between the high schools to see which group of 25 students can cut back the most on their car trips and carbon output.

That will help answer the question of how much pollution people can save just by altering transportation behavior. And hopefully, the participants here are young enough that those transportation choices might continue after the program has ended. Once they get used to walking or biking, for instance, maybe they'll make that a regular form of transportation.

That, of course, doesn't ameliorate the answer to the other burning question – that, yes, the cool phone goes away when the pilot program ends.

Listen to the Tracking Carbon through Your Cell Phone radio report online.

I haven't talked about the elderly in my blog entries so far, but they make up a growing segment of the U.S. population. Those my age– 50-ish– who don't like to think of themselves as baby boomers, will be in that demographic in no time. And many of us worry, sometimes a lot, about finding the best place for our elderly parents to spend their last years.

Research shows that to be healthy physically and psychologically, when we grow old we should stay connected to others. My father moved into an apartment that he had built next to my sister's house in Maryland. My mother and father-in-law are still able to live in their home in Orinda after more than 40 years there. My grandmother on my mother's side lived for nearly 100 years. She spent the last 20 or so years of her life in a community, where everyone had their own apartment, but everyone was responsible, according to their ability, to see to the safety and well being of the others. She rode with three other elderly women to daily Mass and shopping in a big blue Cadillac.

Recent research results published in the journal Environmental Health Perspectives shows that the buildings we live in influence whether we stay connected– and stay healthy– or not. Researchers from the University of Miami, the University of Maine, and Lehigh University in the departments of medicine, education, human development, and architecture, studied a community of mostly elderly, Hispanic, and low-income people in a place called East Little Havana, a neighborhood in Miami. They gathered information about the health and lifestyles of more than 250 people over the course of two years, as well as the buildings they occupied.

Here is a summary of their findings:

1. People who live on blocks where there is a high percentage of porches, stoops, and with buildings built with windows overlooking sidewalks were healthier and happier than those on blocks with fewer of these architectural features. Interestingly, people in buildings with low windowsills out front (less than about a meter between the bottom of the window and the main level of the first floor) were more likely to feel isolated than those with higher windowsills. The researchers speculate that residents felt a lack of privacy with the low windows that made them feel vulnerable, and therefore less likely to interact with people outside the home.

2. People in East Little Havana who lived on blocks with a high level of first floor parking garages did worse physically and psychologically than those living on blocks with more buildings that had people, not cars, living on the first floors. Since newer buildings tend to have the first floor parking, it seems that buildings built before cars became widely available, say pre-1945, are more conducive to the health and well being of their elderly occupants.

The Cadillac my grandmother rode in? It was parked in a parking lot.

The pilot project at UC Berkeley called Mobile Millennium uses cell phones as data points to show traffic patterns in real time.

To become an early adopter of the technology, you must have an unlimited data plan on a mobile phone with a GPS system. If you have that, you can sign up here.

Project leader Alex Bayen says that it's not just a breakthrough in how we can gauge traffic, but also a scientific breakthrough – that is, it was a challenge to take random data points, some in motion, some not, and to turn them into usable traffic information. This is how Alex Bayen put it.

Audio clip: Adobe Flash Player (version 9 or above) is required to play this audio clip. Download the latest version here. You also need to have JavaScript enabled in your browser.

And he adds that, as cell phones get more memory and more devices on them, they will become more central in our lives.

Audio clip: Adobe Flash Player (version 9 or above) is required to play this audio clip. Download the latest version here. You also need to have JavaScript enabled in your browser.

The science of place-based reporting is a burgeoning field. A program at UCLA, for example, uses cell phone information to create a personal environmental risk assessment and a UC Berkeley study monitors currents in the Sacramento River.

Listen to the Dialing in on Traffic radio report online.