Jinglin Jiang and Brandon Boor

Mopping produces pollutants similar to vehicle emissions

The fresh-scented products used to clean our homes and offices come with risks to our respiratory health. The chemicals used to create scents such as lemon and pine pollute indoor air with nano-sized particles in similar ways that motor emissions affect the air we breathe outdoors, according to a new study published in the journal Science Advances.

“It’s not only the direct emissions released from these various cleaning products, but also the different chemical reactions that can occur in the air,” said Brandon Boor, associate professor of civil engineering and an author on the study. “These are very reactive molecules that contribute to outdoor air pollution and smog. We wanted to investigate whether the same chemical transformations were occurring inside buildings and if so, what concentrations of secondary pollutants are produced.”

The chemical compounds limonene and alpha-pinene are added to many common household products such as cleaning and personal care products, air fresheners, candles and aromatherapy products to create a pleasant scent. They’re also found in nature — limonene in citrus peels and alpha-pinene in pine trees. It’s when the chemicals are released and mixed with ozone that they react and become dangerous.

The experiment, conducted in partnership with researchers at Indiana University, took place within a contained room that replicated a typical indoor office environment. Cleaning products were used to mop the floor and wipe down tables and other surfaces. The researchers then measured the volatile organic compounds present in the air for 90 minutes after cleaning.

“People in the United States spend more than 90% of their time indoors, especially during a pandemic,” said Jinglin Jiang (MS’18), a PhD student in civil engineering who ran the data analysis on the study. “By creating a well-controlled indoor environmental system, we can calculate the emission rate for these indoor pollutants and extrapolate to different indoor environments.”

The researchers found that mopping and cleaning under normal conditions indoors creates high concentrations of radicals in the air, initiating a chain of complex chemical reactions that ultimately form small nano-sized particles called ultra-fine aerosols. This process of new particle formation has been widely studied in outdoor environments, but less so indoors. Data from this study suggests the average person would breathe in about 1 billion to 10 billion nanoparticles each minute. That level of pollution is equivalent to emissions produced by vehicle traffic in a large city.

These ultra-fine aerosols have the potential to penetrate deep into our respiratory system and then be transported throughout the body, possibly causing cardiovascular health issues. Although outdoor air quality is regulated because of its impact on public health, indoor air quality remains largely unregulated.

“There are two ways to minimize the harmful effects when using these cleaning products,” Jiang said. “Creating a better control strategy for the indoor ventilation system to dilute the pollutants and wearing personal protective equipment, such as N95 face masks.”

Renovating ventilation and filtration systems is costly and unlikely to occur on a widespread basis without governmental enforcement, much like the Clean Air Act curbing outside emissions when it was passed in 1963. Individuals who work as custodians or house cleaners face the highest risks due to prolonged exposure to aerosols at high concentrations. Futher, they may not have a choice in the type of products they use. When you do have a choice, Boor suggests avoiding use of limonene and alpha-pinene products as much as possible.

“We need to consider the long-term, cumulative effects of repeated exposure to chemicals and aerosols produced by scented household products,” he said. “The mindset is that when you smell these pleasant aromas, you think ‘the house is clean.’ But clean air should have no scent.”