# Can air pollution affect the observed positions of stars?

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I live in a big suburban area where pollution is quite high, and I have been testing a sextant by measuring the angle between pairs of stars. I compared the measured angle with the one obtained from ephemerides, where the latter takes account of the alteration of the body altitude due to refraction in the atmosphere.

For instance, I measured the angle between Castor and Pollux, both at apparent altitudes of ~ 39 degrees.

The comparison works pretty well, but the sextant appears to systematically overestimate the angle by ~ 1'. Can the air pollution in my area (not light pollution) alter the refraction index of the surrounding air mass and thus be responsible for this discrepancy?

Thanks!

The air pollution has a negligible effect on the refraction, because pollution barely affects the air density.

However, the refraction is proportional to the air pressure and inversely proportional to the air temperature in Kelvin. So different weather conditions or ground elevations will result in different refraction values.

## Pollution from new technologies threatens astronomy

This panoramic view of the night sky was taken in Arizona. It shows how light from Winslow, Phoenix and Flagstaff (red and green spots, left to right, starting at 90°) makes it harder to see the stars.

Dan Duriscoe/National Park Service

February 2, 2018 at 6:45 am

OXON HILL, Md. — Astronomers can peer more deeply into the cosmos than ever before. The key is new technology. But new technology can have a dark side. It can create pollution that interferes with astronomers’ work.

Space debris, light pollution and radio waves are the most worrisome. And the situation is getting worse. These types of pollution could prevent astronomers from getting a clear look at the night sky. This warning came from speakers at the annual meeting of the American Astronomical Society on January 9.

Just six decades have passed since the former Soviet Union launched Sputnik, the first artificial satellite. Back then, there was no terrestrial debris around Earth. But conditions have changed. Today, U.S. government scientists track nearly 18,000 objects orbiting Earth. Most are considered space “junk.” These objects range in size from centimeter-long chunks of metal or other spacecraft debris to bus-sized satellites.

And here’s the problem. All of this junk can damage existing space telescopes. What’s more, many also can reflect light, which could potentially confuse observers using ground-based telescopes. From Earth, a glint of light could be a distant star — or just a hunk of metallic junk.

“The worst is yet to come,” warns Patrick Seitzer. He is an astronomer at the University of Michigan in Ann Arbor. “We’re going to double our catalog [of debris] over the next 20 years.” There’s an aerospace company called Boeing, for example, that wants to launch a global network of nearly 3,000 satellites. And collisions between any two of them could cause problems. Any smashup can release thousands of new pieces of debris.

#### Polluting with light

Down on Earth, light pollution is a well-known problem. Artificial lights can outshine the light of stars. And a shift by many nations to illuminating the environment with light-emitting diodes, or LEDs, isn’t helping.

In 2010, LEDs constituted less than 1 percent of the American lighting market. Today, they account for about half. And their share is expected to grow.

LEDs do have environmental and economic benefits. They are long-lived and energy efficient. But they emit a broad spectrum of light, meaning wavelengths that include many colors. These include blue-rich light, which is especially bad for astronomy. Blue light scatters more easily than longer wavelengths, such as yellow light. That scattering worsens sky glow, a sort of haze of light created as the light reflects off of particles in the air above big cities. Sky glow makes it hard to see the stars.

Radio waves, another source of energy, also pose a problem for star gazers. Astronomers search space for radio waves generated by stars and galaxies. But Earth-based sources of this energy can be confused for those signals. Those terrestrial radio sources can include Wi-Fi and even driverless cars. For instance, the radar on driverless cars could affect radio astronomy operations up to 100 kilometers (62 miles) away, said Harvey Liszt. He is a radio astronomer at the National Radio Astronomy Observatory, based in Charlottesville, Va.

#### Saving the stars

There is no doubt that technology is affecting the visibility of skies for astronomers across the planet. That’s why the late astronomer Jean Heidmann proposed a radical idea. He suggested putting a telescope on the moon. He’d site it on the far side, away from Earth. There, it would be safe from space debris, light and radio pollution, he noted.

Another, less extreme idea: Impose strict government regulation on radio frequencies. Astronomers may need to expand and secure what are known as “radio quiet” zones. A notable one covers half of West Virginia. It was developed to surround the extremely sensitive Green Bank Observatory. It’s home to the world’s biggest fully steerable radio telescope. In this almost 34,000 square-kilometer (13,000 square-mile) region of radio silence, there is no cell-phone service and almost no radio stations. People here communicate with land-line phones or call from the road at phone booths.

Without a similar effort to safeguard the radio airways, “radio astronomers would lose the ability to observe,” says Liszt. Such action might be the only way, he argues, to preserve a future for Earth-based radio astronomy.

As for artificial light, having none would be best — at least to many astronomers. But most realize that’s almost a futile fight. Still, there are ways to cope. Flagstaff, Ariz., is adopting LED lights. But this city is using what are known as narrow-band amber LEDs. They resemble the yellow, low-pressure sodium lights that many cities have used in the past, and that astronomers prefer. One reason: They limit sky glow.

“Dark skies have become part of the culture here,” said Jeff Hall. He is an astronomer and director of the Lowell Observatory in Flagstaff. He describes it as “a community value. We even have a company called Dark Sky Brewing.”

Such down-to-Earth solutions to pollution may be astronomers’ only hope.

### Power Words

aerospace A research field devoted to the study of Earth&rsquos atmosphere and the space beyond or to aircraft that travel in the atmosphere and space.

astronomy The area of science that deals with celestial objects, space and the physical universe. People who work in this field are called astronomers.

cosmos (adj. cosmic) A term that refers to the universe and everything within it.

culture (n. in social science) The sum total of typical behaviors and social practices of a related group of people (such as a tribe or nation). Their culture includes their beliefs, values and the symbols that they accept and/or use. Culture is passed on from generation to generation through learning.

debris Scattered fragments, typically of trash or of something that has been destroyed. Space debris, for instance, includes the wreckage of defunct satellites and spacecraft.

LED (short for light emitting diode) Electronic components that, as their name suggests, emit light when electricity flows through them. LEDs are very energy-efficient and often can be very bright. They have lately been replacing conventional lights for home and commercial lamps.

light pollution The intrusion of unwanted light into areas that would naturally remain dark. Light pollution interferes with our ability to view the night sky. It also alters the circadian rhythms of plants, animals and people.

moon The natural satellite of any planet.

network A group of interconnected people or things.

observatory (in astronomy) The building or structure (such as a satellite) that houses one or more telescopes.

orbit The curved path of a celestial object or spacecraft around a star, planet or moon. One complete circuit around a celestial body.

phenomenon Something that is surprising or unusual.

pristine An adjective referring to something that is in original or near-original condition. It means something is somewhat old but in a seemingly &ldquountouched&rdquo or unaltered condition.

radar A system for calculating the position, distance or other important characteristic of a distant object. It works by sending out periodic radio waves that bounce off of the object and then measuring how long it takes that bounced signal to return. Radar can detect moving objects, like airplanes. It also can be used to map the shape of land &mdash even land covered by ice.

radio waves Waves in a part of the electromagnetic spectrum. They are a type that people now use for long-distance communication. Longer than the waves of visible light, radio waves are used to transmit radio and television signals. They also are used in radar.

range The full extent or distribution of something. For instance, a plant or animal&rsquos range is the area over which it naturally exists. (in math or for measurements) The extent to which variation in values is possible. Also, the distance within which something can be reached or perceived.

satellite A moon orbiting a planet or a vehicle or other manufactured object that orbits some celestial body in space.

sky glow The dome of light that surrounds cities at night. Sky glow is caused by particles in the air that scatter light from street lights, car lights and other sources of artificial light. Sky glow is one of three types of light pollution.

star The basic building block from which galaxies are made. Stars develop when gravity compacts clouds of gas. When they become dense enough to sustain nuclear-fusion reactions, stars will emit light and sometimes other forms of electromagnetic radiation. The sun is our closest star.

telescope Usually a light-collecting instrument that makes distant objects appear nearer through the use of lenses or a combination of curved mirrors and lenses. Some, however, collect radio emissions (energy from a different portion of the electromagnetic spectrum) through a network of antennas.

terrestrial Having to do with planet Earth, especially its land. Terra is Latin for Earth.

wavelength The distance between one peak and the next in a series of waves, or the distance between one trough and the next. Visible light &mdash which, like all electromagnetic radiation, travels in waves &mdash includes wavelengths between about 380 nanometers (violet) and about 740 nanometers (red). Radiation with wavelengths shorter than visible light includes gamma rays, X-rays and ultraviolet light. Longer-wavelength radiation includes infrared light, microwaves and radio waves.

### Citations

Meeting:​​ ​ R. Green et al. The triple threat to multi-wavelength observational astronomy. 231st meeting of the American Astronomical Society, Oxon Hill, Md., January 9, 2018.

Journal:​ J. Heidmann. SETI from the moon: Avoiding radio pollution for future radio-astronomy. Highlights of Astronomy. 1998, p. 996. doi: 10.1007/978-94-011-4778-1_119.

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5. Understand all elements of the activity before performing it. Ask questions if you do not understand.
6. Use only the same equipment and quantities of materials suggested in the directions.
7. Make certain all people and property in the area of your science activity are well protected and informed.

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## Barrier Island Astronomy

I've been tasked with teaching the Astronomy Merit Badge to my son's Scout Troop. One opportunity for a night of observation will come on a camping trip to a local barrier island. This trip will involve boating to the island and landing on the beach. The satellite image of the island shows that the only likely clear area, that isn't woods or marsh, will be the beach. Naturally, I'll be traveling light and carrying my second-string equipment. I may simply use the occasion to teach constellations as I really don't want to risk/expose expensive gear to the sand and salt.

### #3 Aleko

Sounds like Cumberland Island. Awesome!

I doubt I'd bring a scope, but I would at least bring some binoculars to pass around. Maybe scouts who have them could bring their own. The Milky Way will be kicking overhead, and it would be a great experience for the scouts to scan the MW. You can even use your laser pointer to lead them to a few easy binocular deep sky objects.

+1 on the bug spray, but being from Savannah, I imagine you already know that. :-)

Edited by Aleko, 10 September 2018 - 10:12 AM.

### #4 RyanSem

Have to agree I wouldn't bring the expensive equipment, especially if you're boating across a channel to the island. Just too much risk for the salt spray along with sand once you get on the beach. If you had a cheapo scope it would be a different story, but if it's dark enough and the milky way is visible I'm sure they'll be entranced enough with that. (I know I was when I did astronomy outings in the scouts!)

### #5 epee

Heh, Deet and the Thermocell are the first things getting packed. Noc's and a laser are a given, I'm debating taking my Infinity 102 refractor as it wide-field views of the Milky Way would be awesome. While the scope would be easy to replace the eyepieces (NOT my good set) would be more valuable. I'd likely have those double boxed small tackle box inside a water-resistant tool box.

Edit: On second thought a messenger bag, strapped to me, would probably do a better job of staying out of the sand.

More thoughts and suggestions are welcome!

Edited by epee, 10 September 2018 - 10:40 AM.

### #6 Myk Rian

Andromeda is an easy target with binos.

### #8 epee

These are full-fledged Scouts so a couple of them are bigger than, 6' 2" me! Porters are not a problem

I've said before that I bought my equipment to use and not to adore, so now's the time to ante-up . It may also be a time to invest in one of the Harbor Freight "Apache" cases.

### #9 GeneT

It is doable, but as you noted, sand and salt is the enemy of optical equipment. Keep the items well covered, and wipe them down when finished viewing.

### #10 kappa-draconis

A waterproof planisphere could be a fun thing to bring. A dimmer red-light flashlight for preserving night vision, too.

### #11 starcanoe

Maybe try some observing from under the water. you'll never complain about bad seeing again !

### #12 Keith NC

Like the suggestion of binoculars. Suspect you could find other families who could send their scout with a pair of binoculars. A binocular tour of the sky should provide tons of teaching opportunities

### #13 epee

Indeed, Binos, a tripod mount, green laser, planisphere, and light discipline for sure. I'm still leaning toward my Infinity 102 and the eyepieces my last big purchase "retired".

Of course this is for a trip in October and like I tried to explain "You can SAY we're going to work on the Astronomy Merit Badge, but the weather might say otherwise. "

### #16 starcanoe

Say what you will. but I'm seeing decent detail on Mars with my 6 inch f 8 dob with a 10mm Vite. they work pretty decently at slow f ratios.

### #17 epee

Hey, I'm glad their working for you. Most of the stuff I'm looking at taking costs more, likely due to the amount of glass, but probably isn't much, if any, any better quality-wise.

This is a simple and clear issue, with a unique answer. I see other replies mentioning weather conditions, dark adaptation and so on. That's just so much hand waving, given that the first thing you said was "I've always lived in somewhat large cities".

The core problem here, by a very wide margin, is light pollution if you live in a large city. This is the one factor, above everything else, that affects your ability to see the stars.

Here's a light pollution map:

The white zones are the worst, and they are in the middle of the cities. Black zones are the best.

Here's a somewhat better (but not perfect) comparison of a dark sky versus light polluted sky (your picture was taken with a very long exposure that doesn't look very realistic):

The dome of light above the city is very visible if imaged from afar:

Long exposure pictures in cities will reveal the orange skyglow, which is the main reason why you can't see the stars - it's like noise masking off the faint light from the distant objects:

Light pollution affects primarily the observations of faint objects, such as nebulae or distant galaxies. Bright objects such as the Moon, the big planets, or some of the bright stars, are not affected by light pollution.

Using a telescope with a large aperture alleviates the effects of light pollution to some extent, but it cannot work miracles. A dark sky is always better.

Usually a 1 hour drive away from the city will bring you in a place with dark sky, free of light pollution - but it depends on several factors. In such a place you should be able to see the Milky Way with your naked eye. The Andromeda galaxy also is visible with the naked eye if the sky is dark enough.

We will do the requirements marked as [1st Session] during our first class, those marked as [2nd Session] during our second class. In between the 1st and 2nd sessions, you will do those requirements marked as [Homework]. Write your answers in your own words. If you have questions, please send me an e-mail.

The evening before the 2nd Session, Friday, March 25th, we will meet at 6pm at our class site (where we met for the 1st Session at Buckeye Hills Regional Park) to plan and execute our 3-hour observation session (9b). If you cannot find us that evening, please call Keith at 480-297-4240.

If you work ahead and finish the [2nd Session] requirements prior/during our second class, you can review your work with me and get your blue card signed off. If you don’t finish, you can still get a partial on your blue card by having me sign off before you leave camp after our second class. Please contact me anytime after the the second class to finish your requirements and get your blue card signed off.

## Contents

Some basic properties of the human eye are:

• Quick autofocus from distances of 25 cm (young people) to 50 cm (most people 50 years and older) to infinity. [citation needed] : about 1 arcminute, approximately 0.02° or 0.0003 radians, [1] which corresponds to 0.3 m at a 1 km distance. (FOV): simultaneous visual perception in an area of about 160° × 175°. [2]
• Ability to see faint stars up to +8 magnitude under a perfectly dark sky. [3] (brightness) to ±10% or 1% of intensity – in a range between night and day of 1:10,000,000,000. [citation needed] of 10–20' (3–6 m per 1 km), see the measurements of Tycho Brahe. [citation needed]
• Interval estimations (for example at a plan on paper) to 3–5%. [citation needed]
• Unconscious recognizing of movement (that is "alarm system" and reflexes). [citation needed]

Visual perception allows a person to gain much information about their surroundings:

• the distances and 3-dimensional position of things and persons
• the vertical (plumb line) and the slope of plain objects
• luminosities and colors and their changes by time and direction

The visibility of astronomical objects is strongly affected by light pollution. Even a few hundred kilometers away from a metropolitan area where the sky can appear to be very dark, it is still the residual light pollution that sets the limit on the visibility of faint objects. For most people, these are likely to be the best observing conditions within their reach. Under such "typical" dark sky conditions, the naked eye can see stars with an apparent magnitude up to +6 m . Under perfect dark sky conditions where all light pollution is absent, stars as faint as +8 m might be visible. [4]

The angular resolution of the naked eye is about 1′ however, some people have sharper vision than that. There is anecdotal evidence that people had seen the Galilean moons of Jupiter before telescopes were invented. [5] Uranus and Vesta had most probably been seen but could not be recognized as planets because they appear so faint even at maximum brightness Uranus' magnitude varies from +5.3 m to +5.9 m , and Vesta's from +5.2 m to +8.5 m (so that it is only visible near its opposition dates). Uranus, when discovered in 1781, was the first planet discovered using technology (a telescope) rather than being spotted by the naked eye.

Theoretically, in a typical dark sky, the dark adapted human eye would see the about 5,600 stars brighter than +6 m [6] while in perfect dark sky conditions about 45,000 stars brighter than +8 m might be visible. [4] In practice, the atmospheric extinction and dust reduces this number somewhat. In the center of a city, where the naked-eye limiting magnitude due to extreme amounts of light pollution can be as low as 2 m , as few as 50 stars are visible. Colors can be seen but this is limited by the fact that the eye uses rods instead of cones to view fainter stars.

The visibility of diffuse objects such as star clusters and galaxies is much more strongly affected by light pollution than is that of planets and stars. Under typical dark conditions only a few such objects are visible. These include the Pleiades, h/χ Persei, the Andromeda Galaxy, the Carina Nebula, the Orion Nebula, Omega Centauri, 47 Tucanae, the Ptolemy Cluster Messier 7 near the tail of Scorpius and the globular cluster M13 in Hercules. The Triangulum Galaxy (M33) is a difficult averted vision object and only visible at all if it is higher than 50° in the sky. The globular clusters M 3 in Canes Venatici and M 92 in Hercules are also visible with the naked eye under such conditions. Under really dark sky conditions, however, M33 is easy to see, even in direct vision. Many other Messier objects are also visible under such conditions. [4] The most distant objects that have been seen by the naked eye are nearby bright galaxies such as Centaurus A, [7] Bode's Galaxy, [8] [9] [10] Sculptor Galaxy, [10] and Messier 83. [11]

Five planets can be recognized as planets from Earth with the naked eye: Mercury, Venus, Mars, Jupiter, and Saturn. Under typical dark sky conditions Uranus (magnitude +5.8) can be seen as well with averted vision, as can the asteroid Vesta at its brighter oppositions. The Sun and the Moon—the remaining noticeable naked-eye objects of the solar system—are sometimes added to make seven "planets." During daylight only the Moon and Sun are obvious naked eye objects, but in many cases Venus can be spotted in daylight and in rarer cases Jupiter. Close to sunset and sunrise, bright stars like Sirius or even Canopus can be spotted with the naked eye as long as one knows the exact position in which to look. Historically, the zenith of naked-eye astronomy was the work of Tycho Brahe (1546–1601). He built an extensive observatory to make precise measurements of the heavens without any instruments for magnification. In 1610, Galileo Galilei pointed a telescope towards the sky. He immediately discovered the moons of Jupiter and the phases of Venus, among other things.

Meteor showers are better observed by naked eye than with binoculars. Such showers include the Perseids (10–12 August) and the December Geminids. Some 100 satellites per night, the International Space Station and the Milky Way are other popular objects visible to the naked eye. [12]

Many other things can be estimated without an instrument. If an arm is stretched the span of the hand corresponds to an angle of 18 to 20°. The distance of a person, just covered up by the outstretched thumbnail, is about 100 meters. The vertical can be estimated to about 2° and, in the northern hemisphere, observing the Pole Star and using a protractor can give the observer's geographic latitude, up to 1 degree of accuracy.

The Babylonians, Mayans, ancient Egyptians, ancient Indians, and Chinese measured all the basics of their respective time and calendar systems by naked eye:

• the length of a year and a month to ±0.1 hour or to better than 1 minute (0.001%)
• the 24 hours of a day, and the equinoxes
• the periods of the planets were calculated by Mayan astronomers, to within 5 to 10 minutes accuracy in the case of Venus and Mars.

In a similar manner star occultations by the moon can be observed. By using a digital clock an accuracy of 0.2 second is possible. This represents only 200 meters at the moon's distance of 385,000 km.

Observing a nearby small object without a magnifying glass or a microscope, the size of the object depends on the viewing distance. Under normal lighting conditions (light source

1000 lumens at height 600–700 mm, viewing angle

35 degrees) the angular size recognized by naked eye will be round 1 arc minute = 1/60 degrees = 0.0003 radians. [1] At a viewing distance of 16" =

400 mm, which is considered a normal reading distance in the US, the smallest object resolution will be

0.116 mm. For inspection purposes laboratories use a viewing distance of 200–250 mm, [ citation needed ] which gives the smallest size of the object recognizable to the naked eye of

55-75 micrometers). The accuracy of a measurement ranges from 0.1 to 0.3 mm and depends on the experience of the observer. The latter figure is the usual positional accuracy of faint details in maps and technical plans.

A clean atmosphere is indicated by the fact that the Milky Way is visible. Comparing the zenith with the horizon shows how the "blue quality" is degraded depending on the amount of air pollution and dust. The twinkling of a star is an indication of the turbulence of the air. This is of importance in meteorology and for the "seeing" of astronomy.

Light pollution is a significant problem for amateur astronomers but becomes less late at night when many lights are shut off. Air dust can be seen even far away from a city by its "light dome".

## Sources of air pollution

There are various sources of air pollution, both anthropogenic and of natural origin:

• burning of fossil fuels in electricity generation, transport, industry and households
• industrial processes and solvent use, for example in chemical and mineral industries
• agriculture
• waste treatment
• volcanic eruptions, windblown dust, sea-salt spray and emissions of volatile organic compounds from plants are examples of natural emission sources.

## Exposed to wildfire smoke? 5 questions answered

Flames and smoke shroud State Route 33 as a wildfire burns in Ventura, California, December 5, 2017. Image Daniel Dreifuss via AP.

Editor’s note: Wildfires once again are raging in California – this time in the Los Angeles area, where five fires are currently burning. As of December 7, 2017, the fast-moving Thomas fire alone had burned more than 65,000 acres in three days. State agencies are issuing air quality alerts due to wildfire smoke. Atmospheric chemist Richard Peltier explains why smoke from wildfires is hazardous and what kinds of protection are effective.

What substances in wildfire smoke are most dangerous to human health? What kinds of impacts can they have?

Wood smoke contains a mixture of microscopic droplets and particles and invisible gases that spread downwind from the fire source. Surprisingly, relatively few studies have investigated the types of exposures we are now seeing in California. Most studies focus on very controlled laboratory experiments, or forest fire fighters who are working on controlled burning, or exposures people in developing nations experience when they use primitive cookstoves. None of these accurately reflects conditions that Californians are experiencing now.

Wood smoke is a very complicated mixture of material in the air, and much of it is known to affect human health. It comes from lots of different fuel sources, including mature trees, dried leaves, forest litter and, unfortunately, local homes. The emissions vary depending on what material is burning and whether it is smoldering or in flames.

Smoke streams from several fires in Southern California on December 5, 2017. Image via NASA Earth Observatory.

For the most part, wildfire smoke is a mixture of carbon monoxide, volatile organic carbon and particles that include alkaline ash, black carbon and organic carbon, which usually contains polyaromatic hydrocarbon, a known cancer-causing agent.

Is a brief exposure, say for a few hours, dangerous, or is smoke mainly a concern if it lingers for days? How does distance from the fire affect risk?

We don’t fully know how the size and length of the dose affect risks, but the longer you are exposed to pollutants from wood smoke, the higher the risk of developing smoke-related illnesses. Short-term exposures to intense smoke can lead to lung and cardiovascular problems in some people, especially if they are already susceptible to these diseases. Longer-term exposure over a few days or weeks increases the risk and the chance of health impacts as your cumulative dose increases.

Smoke tends to become more diluted with distance from the source, but there really isn’t any way to estimate a safe distance where the pollutants are so diluted that they pose no risk. Eventually rainfall will clean all of this pollution from the atmosphere, but that can take days or even weeks. In the meantime, these pollutants can travel thousands of miles. That means air pollution from wildfires may threaten people who are far downwind.

Image of a plume of high-altitude smoke from a forest fire near Alaska, observed in northern Quebec, Canada, more than 2,000 miles away. Image via Richard Peltier.

How do the worst pollution levels from wildfires in California compare to bad air days in a megacity like Beijing or Mumbai?

The concentrations of pollution in communities downwind of these fires are on par with what we see in rapidly growing cities such as Mumbai and Beijing. But there is an important difference. In California these pollutants affect a relatively small geographic area, and the affected areas can rapidly shift with changing weather patterns. In locations like Mumbai and Beijing, high concentrations are sustained across the entire region for days or even weeks. Everyone in the community has to endure them, and there is no practical escape. For now, though, some Californians are experiencing what it’s like to live in a developing country without strong air pollution controls.

How should people in smoky areas protect themselves? Are there remedies they should avoid?

The most effective way to protect yourself is by staying with friends or family who live far away from the smoke. People who can’t leave the area should close windows and doors, and apply weather sealing if they detect smoke leaking in. Even masking tape can be reasonably effective. But most houses leak outside air indoors, so this strategy isn’t foolproof.

Portable high-efficiency filter devices – often marketed as HEPA – can remove indoor air pollution but often are too small to be effective for an entire house. They are best used in individual rooms where people spend a great deal of time, such as a bedroom. And they can be very expensive.

N95 mask. Image via Max-Leonhard von Schaper.

Products marketed as air fresheners that use odorants, such as scented candles or oil vaporizers that plug into an outlet, do nothing to improve air quality. They can actually make it worse. Similarly, products that “clean” the air using ozone can release ozone into your home, which is very hazardous.

Personal face mask respirators can also be effective, but not the cheap paper or cloth masks that many people in developing countries commonly use. The best choice is an N95-certified respirator, which is designed to protect workers from hazardous exposures on the job.

These masks are made of special fabric that is designed to catch particles before they can be inhaled. Paper masks are meant to protect you from contact with large droplets from someone who might be ill. N95 respirators block particles from entering your mouth and nose. They can be a little uncomfortable to wear, especially for long periods, but are pretty effective, and many retailers sell them.

What else do scientists want to know about wildfire smoke?

We have a pretty good understanding of the pollutants that wildfires emit and how they change over time, but we don’t have a firm grasp of how different health effects arise, who is most susceptible or what the long-term effects may be. It is not easy to predict where and when wildfires will occur, which makes it hard for scientists to evaluate individuals who have been exposed to smoke. Controlled laboratory studies give us some clues about what happens in the human body, but these exposures often are quite different from what happens in the real world.

Wildfire smoke in heavily settled areas like Los Angeles affect thousands of people. We saw similar situations in other cities this year, including Seattle, Portland and San Francisco. And it’s not just a West Coast issue. In late November there were major fires reported in Arkansas, Kansas, Kentucky, Missouri, Oklahoma and Pennsylvania. We need to learn more about how smoke exposure affects people in real-world conditions, during fires and long after they end.

Editor’s note: This is an updated version of an article originally published on October 16, 2017.

## Clouds and soot: Understanding air pollution and atmosphere interactions

As soot particles become compact in their journey through the atmosphere, they scatter and absorb light and can affect respiratory tracts.

When carbon burns—whether it's the charcoal on your barbecue or from a forest fire—soot is released into the atmosphere. But what goes up must come down, so what happens to soot?

When soot particles are "cloud processed" they become more compact. The particles are incorporated into cloud droplets, which leads to the water condensing and evaporating as the droplet moves higher or lower in the atmosphere. Soot that is very compact has traveled far and through clouds, which affects the particles' optical, aerodynamic and surface properties.

To more fully understand how soot particles change in the atmosphere, researchers at Michigan Technological University used the University's cloud chamber to simulate conditions similar to those observed at the Pico Mountain Observatory in the Azores, the Po Valley in Italy, the foothills of the Sierra Nevada mountains, the brick-making Bhaktapur region of Nepal and Mexico City.

Janarjan Bhandari, a postdoctoral researcher in Atmospheric Sciences, Claudio Mazzoleni, professor of physics, and collaborators recently published their findings in the journal Scientific Reports.

In their article, "Extensive Soot Compaction by Cloud Processing from Laboratory and Field Observations," Bhandari, Mazzoleni and collaborators discuss the transformation of soot particles in clouds that changes how the black soot particles absorb light and cause atmospheric warming, as well as how they deposit in lungs and cause respiratory issues in dense urban areas.

Inside the Cloud Chamber

In order to control their experiment on the compaction of soot, Bhandari and Mazzoleni used Michigan Tech's Pi Cloud Chamber.

"In the cloud chamber we have controlled conditions. We send in the particles, we form the cloud and we see how they evolve," Bhandari said. "The particles change in shape. When they are emitted, they have a branch-like structure that crumbles to a compacted structure in the cloud."

First, the researchers burn kerosene in an oil lamp under a ventilation hood. They pressurize the air with a pump to suck the smoke into the chamber. Bhandari said they collected several kinds of samples: directly from the lamp for baseline measurements, from cloud droplets in the chamber using a counter flow virtual impactor, and from residual soot in the chamber that did not interact with cloud droplets.

As soot travels through the atmosphere, it has a greater chance of becoming cloud-compressed, which changes its shape, how aerodynamic it is and the degree to which it scatters sunlight. Credit: Michigan Technological University

The experiments in the cloud chamber have enabled the researchers to understand that the longer soot particles are in the atmosphere, the more opportunities they have to become cloud-processed, and the greater the chance the particles become compacted.

"From our point of view, one of the most interesting parts is that the soot particles are absorbing sunlight because they're black," Mazzoleni said. "Most other atmospheric particles for the most part cool the planet because they reflect sunlight. The soot warms the planet instead."

Reducing the soot emitted into the atmosphere could be an important factor in delaying the worst outcomes of climate change. Additionally, many people living in densely populated cities around the world suffer from respiratory conditions related to pollution. Compacted soot can find its way deep into human lungs removing soot from the atmosphere will clear the air, literally.