Acid Rain Stumpers

An acid (and it's alkaline opposite) is a chemical that's described according to how it reacts when added to water. Acids are rated with a pH on the lower half of the 14-point pH scale and when in contact with pure water (rated 7), they release hydrogen ions. Acids aren't just found in liquid form however, gases and solids can also be considered acidic.

Normal rain usually falls slightly on the acidic side -- with a pH of about 5.6 -- because it reacts with other particles in the atmosphere. Acids are also different from alkalis (frequently called "bases") in taste; bases are generally bitter while acids tend towards a sour sensation.

Although natural processes contribute to the Molotov cocktail of chemicals in the sky, it's manmade pleasures like cars, factories and power plants that have really tipped the scales this time. Pollution shoots gasses such as nitrogen oxides and the supremely nasty sulfur dioxide skyward, where they react with other atmospheric particles like water vapor to form sulfuric and nitric acids.

Our fossil fuel emissions come back to haunt us in the form of wet deposition (acid rain and other forms of acidic precipitation) and dry deposition (settling particles, dust and gasses). And while most regular rain generally falls a bit on the acidic side -- averaging around 5.6 as opposed to the pure water pH rating of 7 -- acid rain basically rates as anything below that.

Acid rain was originally recognized in the 1800s, but it wasn't until the middle of the last century that people really started waking up to the dangers of air pollution in general. One step they took to combat the problem was to build soaring smokestacks that towered like skyscrapers over their diminutive predecessors.

Unfortunately, this was about the worst idea they could have had. While it may have decreased the amount of general air pollution in the direct vicinity of each smokestack, it fueled a huge rise in acid rain. Helping sulfur dioxide and nitrogen oxides reach new heights also lengthens their stay in the atmosphere, giving them more time to turn into acids -- and the ability to spread far and wide before pouring back down.

The Clean Air Act passed by Congress in 1970 was the United States’ first major effort to try and reign in air pollution problems.

Sorry folks, the problem of acid rain has been hanging around despite the fact that it isn't as widely discussed as it was in past decades. Although we have been making headway, there's still a long ways to go -- especially on the global scale.

For example, according to a 2006 BBC article, an official report stated that acid rain in China was up 27 percent since 2000, and in some regions, 100 percent of all rainfall was acidic. So, even if we manage to curtail our unprotected fossil fuel excesses at home, other countries can still send acid-filled rainclouds wafting our way.

Not a pleasant answer, but there you have it. If acid rain -- in both wet and dry forms -- is in the forecast, it'll lead to problems aplenty. Let's start with what it does to man-made objects.

Everything from the hood of your car to the paint on your house suffers from continued exposure to acid deposition. Gravestones, bridges and statues also deteriorate under the persistent and corrosive forces of acid rain; buildings grow dingy and faded. Even important cultural monuments can't escape persecution -- both the Taj Mahal and the Parthenon are worse for wear.

Under ideal conditions, lakes and streams are protected from the slight acidity found in regular rain because the surrounding soil acts like a filter -- it has a buffering capacity that resists fluctuations towards both acidity and alkalinity. But just like the oil filter in your car engine, overuse can clog it up. When that happens, not only are there increased aluminum levels and ample acidification in the soil, but neighboring bodies of water share the same fate.

This leads to a whole host of problems. While some species can tolerate low pH levels, many are dramatically affected. For example, acid-loaded lakes can kill adult fish populations and keep their eggs from hatching. Nitrogen depletes aquatic oxygen levels and can lead to things like harmful algal blooms and the loss of coral reefs.

Researchers have found trees become stunted and unhealthy, while climate change seems to be confounding chances for recovery. An overall decrease in terrestrial, marine and plant diversity follows prolonged exposure to acid rain, and don't forget, any time a link in the chain goes missing, anything higher up will have trouble putting food on the table.

Acid rain won't hurt you directly -- even swimming in an overly-acidic lake isn't a big deal -- but if all the sulfate and nitrate particles floating through the air are inhaled into a person's lungs, they can cause a plethora of problems.

According to the EPA, when those particles are inhaled they raise the risk of asthma, bronchitis and even heart problems. When nitrous oxides react with volatile organic compounds, they form ozone, which has been linked to lung inflammation issues like asthma and emphysema. These invisible little killers can even be carried indoors, so don't assume a good lock will keep them out.

Scientists are finding cases where acid rain -- in moderate amounts -- can actually be relatively good for the environment. How's that? Remember how some species tolerate low-pH soil and water? Well, others positively flourish under those circumstances. According to one study published in the Proceedings of the National Academy of Sciences, acid rain greatly decreases the production of one of the most powerful greenhouse gasses that's taking our climate for a ride.

Vincent Gauci, lead author of the study which was conducted by Open University, said, “Acid rain has such a big impact that it shuts down 30 to 40 percent of the methane in wetlands that are affected by this pollution.”

Methane is the byproduct of bacterial decomposers -- but now those bacteria have been getting competition from sulfur-loving microorganisms.

“When we used all the collected data with a NASA model and applied it to a global scale, it shows that the effect of acid rain from 1960 to 2030 actually reduces methane emissions to below pre-industrial levels” Gauci said. “The effect more than compensates for the increase in methane emission that would be expected as wetlands become warmer."

Although many countries -- including the United States -- have made great strides in reducing acid rain by decreasing how much sulfur dioxide and nitrogen oxides they pump into the atmosphere, acid rain is not a problem that respects borders. Many developing nations around the world lack such strict legislation and are adding mightily to the airborne pollution that triggers acid rain. Let's take a closer look at Asia as an example.

The World Resources Institute has predicted that Asian sulfur dioxide emissions will go up threefold between 1990 and 2010. The South Asia Analysis Group featured a column on their Web site by Hari Sud, which detailed China's continuing dependence on coal with above-average sulfur content.

What's interesting is that at least one Chinese city seems safe from acid rain -- for now. Beijing's roaring dust storms perform a balancing act, according to Zhifan Xu and Guilin Han of the Chinese Academy of Sciences, who published their work in the journal Atmospheric Environment. That's because the alkaline-heavy dust is able to neutralize the air over Beijing; but it's a phenomenon that could be short lived -- projects to decrease those same dust storms could end this protection.

Those are all strategies that can contribute to decreasing the threat of acid rain. Scrubber systems and catalytic converters help keep pollution from reaching the atmosphere, and other cleaner processes can also help decrease harmful emissions. The transition to alternative sources of power from the sun, wind and water are also ways to reduce acid rain Until the fossil-fuel burning era is completely at an end, however, legislation in many countries calls for strategies like cap and trade programs. Basically, limits on emissions are set and allowances are distributed among industry businesses. They can use the credits or, if they don't need the full amount they're granted, they can bank them for future use or sell them to less-clean competitors. Watching your own power use is also a plus, and in many areas people are making an effort to give their local environment a little boost by attempting to counteract acidity when it get out of hand.