Every year, scientists learn something new about the power of lightning. With the help of the satellites they have created a lightning map for the globe, which shows that Rwanda has the most flashes per square kilometer, while the flashes at the polar regions occur rarely. Every year, 1,2 million flashes occur around the world.Laboratory and field research has concluded that some lightning bolts reach the temperature of 30,000 Kelvin (54,540 ºF). This temperature is able to melt sand but also break oxygen and nitrogen molecules into individual atoms. What most of us didn’t know about the lightnings is that each flash produces a quantity of nitrogen oxide gas (NOx) that in combination with sunlight and other gases in the atmosphere is able to produce ozone. Ozone is very good is place higher in the stratosphere as it blocks ultraviolet radiations. The problem with ozone is that on ground level it can be deadly to humans and plants and in the higher atmosphere it’s a potent greenhouse gas.
Since 1827 when the German chemist Justin von Liebig first observed that lightning produced NOx, the gas was always in the attention of the scientists. They estimated that the lightning is responsible for about 10% for the total NOx found in the atmosphere, while the rest of 90% comes from fossil fuel combustion, microbes in the soil and forest fires: “There’s still a lot of uncertainty about how much NOx lightning produces. Indeed, even recent published estimates of lightning’s global NOx production still vary by as much as a factor of four. We’re trying to narrow that uncertainty in order to improve the accuracy of both global climate models and regional air quality models” said Kenneth Pickering who studies lightning at NASA’s Goddard Space Flight Center in Greenbelt.
With data from aircraft and satellites, Pickering and Goddard colleague Lesley Ott have recently concluded that lightning produces more NOx in the mid-latitude and subtropical climate and has a lower impact on the surface air quality. In July, Ott and Pickering have published an article in the Journal of Geophysical Research saying that each flash of lightning on average in the several mid-latitude and subtropical thunderstorms studied turned 7 kilograms (15.4 pounds) of nitrogen into chemically reactive NOx: “In other words, you could drive a new car across the United States more than 50 times and still produce less than half as much NOx as an average lightning flash.” By multiplying 1,2 billion of flashes with 7 kilograms of NOx, you will get 8.4 million metric tons of NOx per year, which is much higher then prior estimations.
Most of the NOx is produced higher in the atmosphere as most the lightnings occur inside the cloud rather than cloud-to-ground. The produced intracloud NOx stays in higher quantity a this high level in the atmosphere but a part is also transferred to a higher level. “One of the things we’re trying to understand is how much ozone changes caused by lightning affect radiative forcing, and how that might translate into climate impacts. If a warming globe creates more thunderstorms, that could lead to more NOx production, which leads to more ozone, more radiative forcing, and more warming” emphasized Pickering in his theory. Even though some global modeling studies suggested Pickering’s theory as a real case, it has not been proven by field observations yet.
The findings could mean a huge impact on air quality on regional level. Scientists from the U.S. Environmental Protection Agency (EPA), started to collect some data for a widely-used air quality model called the Community Multi-scale Air Quality Model. “Lightning is one of the smaller factors for surface ozone levels, but in some cases a surge of ozone formed from lightning NOx could be enough to put a community out of compliance with EPA air quality standards during certain times of the year” said Pickering.
Pickering also said that the 7 kilograms per flash value was obtained without taking into consideration lightnings from storms in the tropics, where most of the Earth’s lightnings occurs. The data for tropical regions became available only recently.