‘Thirdhand’ smoke can hitchhike to non-smoking sites | Science News for Students

‘Thirdhand’ smoke can hitchhike to non-smoking sites

Harmful cigarette residues may hitchhike to non-smoking sites
Jul 17, 2018 — 6:45 am EST
close up of a teenager's hands with sparkly nail polish and holding a lit cigarette

Toxic particles of so-called “thirdhand smoke” can settle on clothing. When the smoker comes indoors, those particles can go airborne again to pollute a new site.


Even buildings that strictly enforce bans on indoor smoking may never be smoke-free. A new study shows that “thirdhand smoke” — the type that sticks to surfaces — can end up indoors, even in supposedly smoke-free spaces.

So people could end up breathing in harmful chemicals from cigarette smoke, even when they were in a room where no one ever smoked.

Inhaling smoke directly through a cigarette can lead to cancer and many other health problems. The cigarette smoke that people nearby inhale is known as secondhand smoke. It, too, can harm the lungs. Thirdhand smoke is what’s left behind after someone has finished smoking. It’s a mix of nicotine and other chemicals that can create that stale, smoky smell after any visible smoke clears. It sticks to clothing, furniture and walls, where it can linger for hours or days.

Thirdhand smoke is not benign. It, too, can react with other molecules in the air to form cancer-causing substances. 

Peter DeCarlo was surprised to find thirdhand smoke in a classroom at Drexel University in Philadelphia, Pa. DeCarlo is an atmospheric scientist at Drexel. He was setting up an experiment to study the effects of heating and air conditioning on particles in the air. As far as anyone knew, no one had ever smoked in this room being tested. It certain didn’t smell smoky.

DeCarlo wasn’t looking for thirdhand smoke. But once he found its chemical “fingerprint,” he did some detective work to investigate how it got there.

Harmful hitchhikers

Air is a mixture of gases, including nitrogen and oxygen. Microscopic particles of things like pollen, water vapor, soot and pesticides can float in the air. These are called aerosols. DeCarlo’s research team sucked up a small amount of air from the classroom.

Then they used a machine to identify the aerosols in that air. This mass spectrometer (Spek-TRAH-meh-tur) found that nearly three in every 10 of these particles appeared to come from thirdhand smoke. To explore why, they took a closer look at the chemistry of those particles in the air.

Anita Avery is a graduate student working with DeCarlo. She pumped cigarette smoke into a glass container. To do this, Avery used an artificial-smoking machine. This device draws air through a burning cigarette (much as a smoker would). Some of the emitted smoke particles remained stuck to the glass walls, even after the air had cleared.

The next day, Avery pumped fresh air through the container. Then she measured what was in the air as it left the container. Thirdhand smoke particles showed up in what should have been clean air.

Those particles must have come off of the glass walls and hitched a ride on passing aerosols, the researchers now conclude. Nicotine and other chemicals in thirdhand smoke are alkaline — chemicals with a pH higher than 7 (on a scale of 14). Nicotine and other weak bases have a pH close to 7. Those with a far higher pH are considered strong bases.

The researchers now think that as some strong base in air passed by the glass, the nicotine reacted with it and became unstuck. It then attached onto neighboring aerosols, DeCarlo suspects. That would allow the nicotine molecules to float into different rooms as air circulates throughout a building’s heating and cooling ducts.

Ammonia is one example of a strong base that’s common inside buildings. In fact, DeCarlo points out, ammonia is an ingredient in many cleaning products. An ingredient of sweat and urine, it is also released by the human body. Similar reactions with thirdhand smoke particles on someone’s clothing might also release them back into the air.

The researchers described their findings May 9 in Science Advances.

Story continues below video.

Drexel University chemist Peter DeCarlo explains how thirdhand smoke stuck to indoor air particles and traveled through a non-smoking classroom.  
DeCarlo Laboratory /Vimeo.

Stealthy smoke

“This study opens our eyes to the steps that can occur after tobacco smoke enters the air,” says Charles Weschler. He is a chemist at Rutgers University in Piscataway, N.J., who did not work on the new study. But Weschler’s team does focus on indoor-air pollution and the role that clothing can play in transporting it.  

DeCarlo’s group did not study what the new findings might mean for health. The researchers do note, however, that thirdhand smoke could be a hidden danger for nonsmokers in rooms or other spaces shared with smokers. For example, thirdhand smoke could linger in rental cars. Or nonsmokers might encounter the particles on a crowded bus — even in a “non-smoking” hotel room.

DeCarlo usually studies outdoor air pollution. But his new data show why indoor pollution is important. “We spend most of our days in buildings,” DeCarlo points out. What that means, he says, is that “indoors is where most of our exposure to air pollution happens.”

Power Words

(more about Power Words)

aerosol     A group of tiny particles suspended in air or gas. Aerosols can be natural, such as fog or gas from volcanic eruptions, or artificial, such as smoke from burning fossil fuels.

alkaline     An adjective that describes a chemical that produces hydroxide ions (OH-) in a solution. These solutions are also referred to as basic — as in the opposite of acidic — and have a pH above 7.

ammonia     A colorless gas with a nasty smell. Ammonia is a compound made from the elements nitrogen and hydrogen. It is used to make food and applied to farm fields as a fertilizer. Secreted by the kidneys, ammonia gives urine its characteristic odor. The chemical also occurs in the atmosphere and throughout the universe.

base     (in chemistry) A chemical that produces hydroxide ions (OH-) in a solution. Basic solutions are also referred to as alkaline.

benign     Not harmful to one’s health. Malignant, in contrast, means harmful and generally refers to cancer.

cancer     Any of more than 100 different diseases, each characterized by the rapid, uncontrolled growth of abnormal cells. The development and growth of cancers, also known as malignancies, can lead to tumors, pain and death.

chemical     A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

chemistry     The field of science that deals with the composition, structure and properties of substances and how they interact. Scientists use this knowledge to study unfamiliar substances, to reproduce large quantities of useful substances or to design and create new and useful substances. (about compounds) Chemistry also is used as a term to refer to the recipe of a compound, the way it’s produced or some of its properties. People who work in this field are known as chemists.

graduate student     Someone working toward an advanced degree by taking classes and performing research. This work is done after the student has already graduated from college (usually with a four-year degree).

mass     A number that shows how much an object resists speeding up and slowing down — basically a measure of how much matter that object is made from.

microscopic     An adjective for things too small to be seen by the unaided eye. It takes a microscope to view objects this small, such as bacteria or other one-celled organisms.

molecule     An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).

nicotine     A colorless, oily chemical produced in tobacco and certain other plants. It creates the “buzz” associated with smoking. Highly addictive, nicotine is the substance that makes it hard for smokers to give up their use of cigarettes. The chemical is also a poison, sometimes used as a pesticide to kill insects and even some invasive snakes or frogs.

nitrogen     A colorless, odorless and nonreactive gaseous element that forms about 78 percent of Earth's atmosphere. Its scientific symbol is N. Nitrogen is released in the form of nitrogen oxides as fossil fuels burn.

oxygen     A gas that makes up about 21 percent of Earth's atmosphere. All animals and many microorganisms need oxygen to fuel their growth (and metabolism).

particle     A minute amount of something.

pH     A measure of a solution’s acidity or alkalinity. A pH of 7 is perfectly neutral. Acids have a pH lower than 7; the farther from 7, the stronger the acid. Alkaline solutions, called bases, have a pH higher than 7; again, the farther above 7, the stronger the base.

pollen     Powdery grains released by the male parts of flowers that can fertilize the female tissue in other flowers. Pollinating insects, such as bees, often pick up pollen that will later be eaten.

pollutant     A substance that taints something — such as the air, water, our bodies or products. Some pollutants are chemicals, such as pesticides. Others may be radiation, including excess heat or light. Even weeds and other invasive species can be considered a type of biological pollution.

residue     A remnant or material that is left behind after something has been removed. For instance, residues of paint may remain behind after someone attempts to sand a piece of wood; or sticky residues of adhesive tape may remain on the skin after a bandage is removed; or residues of chemicals may remain in the blood after exposure to a pollutant.

secondhand smoke     The gas and smoke particles emitted out of the burning end of a cigarette in addition to the particles exhaled by smokers. This pollution can be toxic and hand into the air (where it is available to be breathed in) for hours. Government scientists report that this secondhand smoke may contain up to 7,000 different chemicals, including hundreds that may be toxic (70 of which can cause cancer). According to the U.S. Centers for Disease Control and Prevention, since 1964, some 2.5 million nonsmokers have died from exposure to secondhand smoke.

smoke     Plumes of microscopic particles that float in the air. They can be comprised of anything very small. But the best known types are pollutants created by the incomplete burning of oil, wood and other carbon-based materials.

smoking     A term for the deliberate inhalation of tobacco smoke from burning cigarettes.

soot     Also known as black carbon, it's the sometimes oily residues of incompletely burned materials, from plastics, leaves and wood to coal, oil and other fossil fuels. Soot particles can be quite small — nanometers in diameter. If inhaled, they can end up deep within the lung.

spectrometer     An instrument that measures a spectrum, such as light, energy, or atomic mass. Typically, chemists use these instruments to measure and report the wavelengths of light that it observes. The collection of data using this instrument, a process is known as spectrometry, can help identify the elements or molecules present in an unknown sample.

tobacco     A plant cultivated for its leaves, which many people burn in cigars, cigarettes, and pipes. Tobacco leaves also are sometimes chewed. The main active drug in tobacco leaves is nicotine, a powerful stimulant (and poison).

water vapor     Water in its gaseous state, capable of being suspended in the air.


Journal: P.F. DeCarlo et al. Thirdhand smoke uptake to aerosol particles in the indoor environment. Science Advances. Published online May 9, 2018. doi: 10.1126/sciadv.aap8368.