American and Chinese scientists are examining whether tiny particles drifting over the U.S. from Asia are shading North America, helping to cool parts of Earth as the globe warms.

The researchers have developed a kit of new tools including an instrument the size of a cigar box that uses a laser to detect the tiny aerosol particles. They include man-made materials like soot and vehicle exhaust, as well as natural items such as desert dust and sea salt.

Since the 1990s, scientists have been discussing using aircraft to inject aerosols, such as sulfates, into the atmosphere as a form of geoengineering to mimic volcanic eruptions that sometimes cool the planet by casting shades of particulate matter. It's controversial, but some scientists see it as one option to limit global warming if nations fail to stem the output of greenhouse gases before a tipping point is reached.

There's accumulating evidence that geoengineering has already started, unintentionally, from the natural forces of Asia's massive summer monsoon. It sends pollutants soaring up the Himalayas, with some reaching the stratosphere, where they are high enough to drift over the Pacific and help shade the Northern Hemisphere.

"This could actually affect the climate. That's the main reason we are looking at this," explained Ru-Shan Gao, a research physicist in the chemical sciences division of NOAA. Using a 3-D printer, Gao designed a "Printed Optical Particle Spectrometer (POPS)," a cigar-box-sized device that's about one-tenth of the size, and one-fifth of the cost, of laser-equipped instruments that can identify and track aerosol particles.

POPS, equipped with a small laser, became the first device to positively identify aerosols floating more than 10 miles above south China. Its success has led to a number of other joint U.S.-China experiments. This summer, scientists produced a report finding that the monsoon amounted to an "efficient smokestack" for Asian pollution, spreading it "throughout the entire Northern Hemisphere." The contribution, about 15 percent of aerosols in total, was similar to the "sum of small volcanic eruptions between 2000 and 2015."

Gao's Chinese colleagues also made some interesting ground-based discoveries. One climate scientist put a POPS in his backpack and rode around Lhasa, the capital of China's Tibet Autonomous Region, in summer 2016. On Buddhist religious holidays, he found that the ritual burning of incense, tree limbs, herbs and huge piles of leaves emitted about 80 percent of the city's aerosol pollution, including a large amount of carcinogens. The finding was another first for POPS.

"It's really hard in these days to do science by yourself," explained Gao, who grew up in China but was initially barred from college because of the Cultural Revolution. Because his family was wealthy and his father was a doctor, he was sent to work in a factory, where he learned mechanics and electronics. After getting his doctorate and his U.S. citizenship, he settled into the "skunk works," a busy, messy laboratory at NOAA's Earth System Research Laboratory in Boulder, Colo., where he often spends weekends tinkering with experimental devices.

He gets help from his friends and his boss, who pulled out a credit card when Gao needed a 3-D printer. He also enjoys working with his counterparts in China.

"I have an advantage that I can talk to them in a more friendly way and get them to collaborate with us," he said.

Findings like his, however, are not always popular in Asia. As Gao noted, China takes measurements of pollutants but doesn't usually share its findings with other countries. India, another huge source of atmospheric pollution, recently allowed European scientists to measure its high-level aerosols, an experiment that also includes flights into Nepal and Bangladesh. But China blocked them. "You can't really talk common sense into these countries," Gao said.

"What we're trying to do is understand the dynamics of the whole stratosphere," he added. "That should be the basis of any discussion of geoengineering. If we don't know the state now, how can you predict the status later?"

This is what's known about the dynamics of the stratosphere: Increasing clouds of low-lying ozone, made from the reaction between sunlight and pollution, are showing up in the western U.S. that have little or no industrial activity. The list of ozone hot spots includes national parks and sparsely populated places in Nevada. Las Vegas, whose major industry is gambling, is also a hot spot.

Under the U.S. Clean Air Act, low-level ozone is a listed pollutant. Nevada Gov. Brian Sandoval (R) insists his state is being unfairly punished for matters beyond its control. He has been pushing for discussions with China to support more clean energy technology and energy efficiency. "This will have significant impact on Nevada and the entire western United States," he predicted.

The Asian summer monsoon is described in one study as one of the "most dramatic and important among all climatic phenomena on Earth." It's linked to the spread of aerosols and greenhouse gases from countries that are among the world's largest emitters.

Another study, published last year in Reviews of Geophysics, lists the man-made aerosols as coming from sulfates, nitrate and black carbon emitted by internal combustion engines, coal-fired power plants, slash-and-burn agricultural practices, and smoke from cooking.

The next accounting from POPS may come next year. Gao is making one unit for a Harvard University team that will include it in a large, maneuverable helium-filled balloon. It's designed to track an aerosol plume in the stratosphere at a height of 70,000 feet.

Could pollution from Asia eventually help us shade the Earth?

"It's plausible," said David Keith, a professor of applied physics at Harvard who is co-director of the balloon experiment. "How much gets up into the stratosphere is unknown. Our experiment will not get at this directly, much as we might like."

Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at