February 11, 2013 – Vol.17 No. 48

DO-IT-OURSELVES WEATHER?

Does air pollution intensify storms?

by Bruce Mulliken, Green Energy News

 

I like shiny black cars, but I'll never own one. I don't call black cars black anyway. I call them dirty black cars. Take your black car through the car wash, or spend a morning washing and waxing it, and it's only clean and shiny until the next rain, then it's dirty and dusty all over again.

We tend to think of rain (or snow) as just water from the sky. It isn't. Droplets of rain have minute particles, like dust, at their core. If it wasn't for that dust, clouds wouldn't be there, nor would the rain that falls from them. Scientists have a better name for that dust: aerosols. If it wasn't for those aerosols – that dust in rain – I would own a black car.

NASA's excellent weekly newsletter Earth Observatory often features images of our lonely planet taken from space, along with detailed descriptions of what's happening below. A recent edition shows satellite photos (and a YouTube video) of ship tracks off the west coast of the US and Canada. Similar to airplane contrails (clouds formed from the exhaust, or aerosols, from high-flying jets) ship tracks are clouds formed when moisture-filled ocean air condenses on the rather dirty exhaust of ships.

shiptracks

Ship's tracks off North America (NASA photo)

NASA describes the photos:

"Amidst the natural marine clouds southwest of Vancouver Island were long, thin, man-made clouds, many of them arising from small source points. The thin clouds were ship tracks—clouds seeded by particles in ship exhaust. Tiny airborne particles (aerosols) act as nuclei or seeds for cloud formation, as water vapor condenses onto them.

"The aerosol particles may be natural – such as desert dust or sea salt – or artificial, including the particles emitted by ships. The particles in ship exhaust are more abundant than natural airborne particles such as sea salt, so they generate more and smaller cloud droplets. Because of this, ship tracks tend to be brighter than other clouds. Water droplets are essentially tiny spheres, and a smaller sphere has a greater surface-to-volume ratio than a bigger sphere. In other words, a littler droplet has a greater surface area, relative to its volume, than a bigger droplet. The greater surface area means more sunlight reflected back into space."

NASA is also very good about including links on it pages for the benefit of research geeks like myself. In another Earth Observatory page "Aerosols: Tiny Particles, Big Impact" NASA makes another connection between aerosols and air pollution:

"The bulk of aerosols – about 90 percent by mass – have natural origins. Volcanoes, for example, eject huge columns of ash into the air, as well as sulfur dioxide and other gases, yielding sulfates. Forest fires send partially burned organic carbon aloft. Certain plants produce gases that react with other substances in the air to yield aerosols, such as the “smoke” in the Great Smoky Mountains of the United States. Likewise in the ocean, some types of microalgae produce a sulfurous gas called dimethylsulfide that can be converted into sulfates in the atmosphere.

"Sea salt and dust are two of the most abundant aerosols, as sandstorms whip small pieces of mineral dust from deserts into the atmosphere and wind-driven spray from ocean waves flings sea salt aloft. Both tend to be larger particles than their human-made counterparts.

"The remaining 10 percent of aerosols are considered anthropogenic, or human-made, and they come from a variety of sources. Though less abundant than natural forms, anthropogenic aerosols can dominate the air downwind of urban and industrial areas.

"Fossil fuel combustion produces large amounts of sulfur dioxide, which reacts with water vapor and other gases in the atmosphere to create sulfate aerosols. Biomass burning, a common method of clearing land and consuming farm waste, yields smoke that’s comprised mainly of organic carbon and black carbon."

So, if something so seemingly minor as ship exhaust can make clouds in the sky, how much of the world's cloudiness, and perhaps weather events themselves, are because of all the other aerosols we're putting into the thin atmosphere, globally, around the clock, day after day?

Consider this. Rain and snow storms (including hurricanes) aren't great masses of clouds and areas of low atmospheric pressure that originate in one place and move to another dumping precipitation along the way. Storms may start as an area of low pressure, but as they move are continuously fed with water-vapor filled air just waiting to mix with some aerosols to make rain or snow.

In the US much of the air that keeps the eastern half of the country warm, comes directly off the surface of the Gulf of Mexico. The Gulf Stream in the Atlantic, which originates at the tip of Florida and nearly parallels the East Coast as it meanders northward, also brings warm air inland if the wind is right.

Further, here in the US, the jet stream, traveling generally West to East in the stratosphere often dips down near the Gulf then heads Northeasterly to quickly exit US airspace usually somewhere between North Carolina and Maine. The jet stream steers weather events.

As it turns out this exit point for the jet stream is directly over the megalopolis in the Northeastern portion of the country that includes the cities of Richmond, Washington, DC, New York and Boston and hundreds of other cities and towns. This megalopolis, and whole Northeast region itself, is also the richest, most densely populated and most economically vibrant part of the country. As you can imagine with the wealth, the busy economy and dense population, it has lots of power plants and vehicles. With those, it is also one of the most polluted, most aerosol laden regions in the United States.

So, what happens if a storm comes along, being steered by the jet stream, headed North or Northeast, and being fed with Gulf of Mexico or even Gulf Stream moisture, suddenly reaches this megalopolis and its aerosols? With all the aerosols in the air for moisture to condense upon, wouldn't there be wetter and more powerful storms than would be otherwise? When waves of warm moist air meet up with abundant aerosols wouldn't there be the potential for an increase in intensity for storms like Hurricane Sandy or blizzard Nemo? Sandy was a weakening tropical storm until it turned west and inland to meet up with another storm, as well as the aerosols of New York area. Nemo was an ordinary Nor'easter until it met with a cold front and copious aerosols of the megalopolis. Sandy lingered inland for days fed with plenty of warm moist air from the south and a ready supply of aerosol nuclei to make more rain. Nemo continued its wrath into the Maritime Provinces of Canada dropping its aerosol-seeded snow all along it's path.

Weathermen always mention warm air and moisture as feeding big storms, but never mention aerosols, especially the man-made type. If they did maybe more would make the connection: This weird weather we're having, we're doing it ourselves.

 

Links.

Earth Observatory:Aerosols: Tiny Particles, Big Impact

Earth Observatory: Ship Tracks off North America

 

Related.

Where are the Hurricanes?

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