Health impacts and demographic inequities from nitrogen dioxide emissions in US homes using gas and propane stoves

By Vijay Kumar MalesuReviewed by Lily Ramsey, LLMMay 8 2024

In a recent study published in Science Advances, researchers quantified indoor nitrogen dioxide (NO₂) emissions from gas and propane stoves and assessed their health impacts and demographic disparities in exposure among United States (U.S.) populations.

Study: Nitrogen dioxide exposure, health outcomes, and associated demographic disparities due to gas and propane combustion by U.S. stoves. Image Credit: M-Production/Shutterstock.com

Background 

Gas and propane stoves, used in over 50 million U.S. homes, emit pollutants like NO₂ and benzene (C₆H₆), often exceeding health safety levels. Long-term NO₂ exposure is linked to severe health issues, including asthma and chronic obstructive pulmonary disease.

Traditional studies lack precision in assessing exposure due to variations in stove usage and ventilation.

Further research is needed to refine exposure assessments and understand the full range of health impacts across different demographics, improving mitigation strategies and policy interventions.

About the study 

In the present study, different terms were clearly defined to standardize the terminology used throughout the research. A "cooktop" was identified as a flat surface featuring two to six cooking elements, while "burners" referred to elements utilizing a gas or propane flame.

"Stoves," or "ranges," were described as freestanding units combining both a cooktop and an oven. The team also distinguished between "outside-venting range hoods," which expel kitchen air outdoors, and "recirculating range hoods," which filter and return air back into the kitchen. 

For measurement purposes, the term "concentration" was utilized for its accessibility, with standard conversions applied based on an assumed temperature of 25°C and atmospheric pressure.

The CONtaminant Transport Analysis Model (CONTAM) multizone indoor air quality model, developed by the National Institute of Standards and Technology (NIST), was pivotal in modeling indoor NO₂ concentrations. The model was validated through comparisons with measured NO₂ levels in various "validation residences," subsequently applying these validated models to other unmeasured residence types.

The methodology incorporated detailed measurements of NO₂ concentrations using advanced analytical equipment. Emission rates from gas and propane stoves were calculated across a diverse set of residences, including both private and rented spaces, across multiple states.

The study carefully calculated NO₂ and carbon dioxide (CO₂) emission rates using enclosed kitchen volumes, employing a tracer gas method to adjust for air exchange in the calculations.

Finally, the validated CONTAM model was used to estimate NO₂ exposure under different environmental, behavioral, and demographic conditions.

These estimates were linked with epidemiological data to assess health impacts, specifically the burden of pediatric asthma attributable to long-term NO₂ exposure from gas and propane stoves. 

Study results 

The present study evaluated the accuracy of the CONTAM indoor air quality model by comparing its predicted NO₂ concentrations against actual measurements taken from 18 diverse residences.

These included a mix of apartments and detached homes, ranging in size and located across various urban areas such as the San Francisco Bay Area, Los Angeles, Denver, Houston, New York City, and Washington, DC.

Different scenarios were tested, including windows open or closed and outside-venting range hoods turned on or off. The results showed a strong correlation between the modeled and actual NO₂ concentrations, with no significant bias detected in the model’s predictions.

In addition to validating the model, the study also examined NO₂ emission factors from gas and propane stoves. Measurements indicated that NO₂ emissions directly correlated with the amount of fossil fuel burned, evidenced by corresponding CO₂ emissions.

Interestingly, no NO₂ emissions were detected from electric or induction stoves. Propane and natural gas stoves showed similar NO₂ emissions per joule of fuel burned, likely due to the similar flame temperatures of methane and propane.

Further tests in bedrooms showed that NO₂ levels could exceed health-based guidelines within minutes when ovens were used without engaging range hoods.

The effectiveness of outside-venting range hoods varied, with some reducing peak NO₂ concentrations significantly while others had minimal impact. On average, these hoods reduced kitchen NO₂ concentrations by about 35%.

The study also modeled long-term and short-term NO₂ exposures from stove use, incorporating factors such as cooking duration, frequency of range hood use, and the efficiency of these hoods.

The findings indicated that long-term and short-term NO2 exposures were significantly higher in smaller residences and households with lower incomes, highlighting socioeconomic disparities in exposure risks.

The racial and ethnic disparities were evident as well, with American Indian or Alaska Native, Hispanic or Latino, and Black households experiencing higher levels of NO₂ exposure compared to White and Asian households. This was partially attributed to the smaller average residence size among the more affected groups.

Behavioral factors like the duration and intensity of stove use played a major role in determining NO₂ exposure. For instance, residences with high stove use saw dramatically higher NO₂ exposure in the short and long term.

The study's sensitivity analysis confirmed that total gas or propane burned was the most critical factor in predicting NO₂ exposure levels, followed by ventilation practices and time spent in the kitchen.