I walked back on a Friday afternoon from Bellevue Clinic and scrolled through my phone. One of my apps told me I had breathed in 1.4 cigarettes in pollution smoke that day. It has become a routine for me to gauge how bad the outdoor air pollution is, and it’s often on the news in the form of “LA/Beijing/Delhi/NYC smog worsened today” or “Air Quality Alert today”.
For many patients who have a history of lung disease, we often recommend avoiding allergens and triggers. We tell patients to stay inside when it is too hot out, when there is a lot of pollen, and when it is cold outside. Our understanding of why this might be wrong hinges on three questions:
- How much less polluted is the home environment compared to the outside?
- What specifically contributes to a safer, or more polluted home environment?
- What can we do as physicians to improve the indoor environment?
Pollution is defined as the introduction of contaminants into the environment causing negative effects.1 The most common known culprits are tobacco smoke, biological pollutants such as dust, mold, pets, asbestos, and others associated with interstitial lung diseases (silica, coal, pigeons, etc.).
Several of the less commonly known malignant compounds are referred to by the WHO as “solid fuels”. Particulate matter is a pollutant that is defined as fine (PM2.5) or coarse (PM10), depending on the diameter of the particle in micrometers. It is generally synthesized by fuel or coal combustion, and is often in high concentrations in indoor environments. There is no known safe level of these particles, but it is defined by the WHO for PM2.5 as 10 micrograms per cubic meter. Most of the US has an annual mean of around 12, but it’s much higher in urban areas. It is strongly associated with chronic disease, poor quality of life, and impaired lung function. Studies have shown that higher levels of PM 2.5 and PM 10 are associated with higher rates of atopic and non-atopic asthma, obesity, stroke, cardiovascular disease, chronic bronchitis, hypertension, diabetes, and mortality.2,3,4
For most of the developing world, indoor pollution is the result of burning of wood or coal for cooking. Open air fires, such as coal and wood stoves, often used in rural communities in places such as South America and East Asia, are associated with very high levels of particulate matter. Close to half of the world’s population still cooks with open fires and solid fuels such as wood, charcoal, kerosene, and feces, without any filters. According to the WHO, 3.8 million deaths are directly attributable to household air pollution from open fires and cooking; these are mostly due to pneumonia, stroke, myocardial infarction, chronic obstructive pulmonary disease, and lung cancer.5 In addition, dirty heating and cooling mechanisms are other large contributors to indoor air pollution. This affects many communities both urban and rural around the world, especially in areas of low-income housing in large urban centers and rural areas without access to electricity.
The landmark 2009 RESPIRE trial was a randomized controlled trial that assessed the impact of changing an open fire stove to a chimney woodstove on the carbon monoxide exposure and pulmonary function of Mayan women in rural Guatemala. Compared to open-coal fires, use of the chimney woodstove, referred to in Spanish as plancha, was associated with a 62% reduction in carbon monoxide exposure and a reduction in wheezing and pulmonary symptoms. This study was invaluable at assessing the dangers of continuing to use coal fires for cooking, especially in homes with poor ventilation. In addition, if the study were allowed to continue, it most likely would have found differences in formal pulmonary function testing.6
Many healthy adults may not be affected in the same way that children are and may not spend much time at home, but for patients who are elderly, immunocompromised, or with chronic disease, much of the time is spent in the home. Studies have now associated spending more time in homes with worsening health in those with pulmonary disease, as higher levels of nitrogen dioxide and particulate matter have been shown to worsen dyspnea, wheezing, and exacerbations in patients with COPD.7,8 In addition, a cohort study showed that indoor heat was associated with worsening COPD symptoms.9
So given all this, how do we approach this as clinicians? Risk factors should be assessed as part of the social history in any patient with chronic pulmonary disease or any home with children or pregnant adults. First, one should ask about allergens: dust mites, pets, cleanliness of the house, presence of water damage or mold growth. Secondly, one should then turn to questioning about indoor pollutants about particulate matter. What type of stove is used, if there is a fireplace or woodburning stove, and the type of ventilation and aeration (windows, how often open) and heating are key points.
And once we identify the problems, what can be done? There have been efforts to improve stoves and clean fuels.10 Replacing gas stoves with electric stoves, and using air purifiers such as HEPA (high efficiency particulate absorbing) filters, have decreased levels of nitric oxide11 as well as particulate matter and carbon monoxide.12,13 In order to decrease the levels of PM2.5 indoors, there are 5 approaches: 1) using cleaner oils such as safflower as opposed to olive oil can reduce primary emission, 2) exhaust ventilation to extract polluted air, 3) portable recirculating air cleaners, and 4) keeping windows open longer and 5) window filters, can all reduce the levels of PM2.5 and prevent the flow from the outside to the indoors.14 A trial to improve nitrogen dioxide levels in schools by replacing these gas heaters led to a reduction in pulmonary symptoms in children with asthma, and over time led to fewer diagnoses of asthma.15
One of the most important interventions is education, as behavioral interventions such as not leaving the gas stove on too long can significantly reduce fuel combustion, which reduces volatile compounds such as nitric oxide12 and keeping windows closed can reduce particulate matter concentrations. Overall, we must do more to improve the quality of the home environment. We must remember we are treating a person who must do a great deal at home. Assessing their cooking habits and heating sources and making recommendations to reduce pollution from those sources is one of the most successful interventions we can make.
Noah Rosenberg is a 3rd year medical student at NYU Robert I. Grossman School of Medicine
Reviewed by George Friedman-Jimenez, MD, Department of Population Health, NYU Langone Health
Image courtesy of Wikimedia Commons
- Merriam-Webster Dictionary. Springfield, MA: Merriam-Webster Inc; 2019. https://www.merriam-webster.com/dictionary/pollution
- Bose S., Diette G.B. (2016) Health Disparities Related to Environmental Air Quality. In: Gerald L., Berry C. (eds) Health Disparities in Respiratory Medicine. Respiratory Medicine. Humana Press, Cham https://link.springer.com/chapter/10.1007/978-3-319-23675-9_3
- Matsui EC, Abramson SL, Sandel MT. Indoor environmental control practices and asthma management. Pediatrics. 2016;138(5):2001-2018. https://pediatrics.aappublications.org/content/138/5/e20162589
- Williams PV. Indoor particulate matter increases asthma morbidity in children with non-atopic and atopic asthma. 2011;128 (Supplement 3):S103-S103. https://pediatrics.aappublications.org/content/128/Supplement_3/S103.1
- World Health Organization. Household air pollution and health. https://www.who.int/news-room/fact-sheets/detail/household-air-pollution-and-health Published May 8, 2018. Accessed September 18, 2019.
- Smith-Sivertsen T, Diaz E, Pope D, et al. Effect of reducing indoor air pollution on women’s respiratory symptoms and lung function: the RESPIRE Randomized Trial, Guatemala. Am J Epidemiol. 2009;170(2):211-220. https://www.ncbi.nlm.nih.gov/pubmed/19443665
- Hansel NN, McCormack MC, Bell AJ, et al. In-home air pollution is linked to respiratory morbidity in former smokers with chronic obstructive pulmonary disease. Am J Resp Crit Care Med. 2013:187(10):1085-1090. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3734614/
- Chi MC, Guo SE, Hwang SL, Chou CT, Lin CM, Lin YC. Exposure to indoor particulate matter worsens the symptoms and acute exacerbations in chronic obstructive pulmonary disease patients of southwestern Taiwan: A pilot study. Int J Environ Res Public Health. 2016;14(1). pii: E4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5295255/
- McCormack MC, Belli J, Waugh D, et al. Respiratory effects of indoor heat and the interaction with air pollution in chronic obstructive pulmonary disease. Ann Am Thorac Soc. 2016;13(12):2125-2131. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5291496/
- Puzzolo E, Pope D, Stanistreet D, Rehfuess EA, Bruce NG. Clean fuels for resource-poor settings: A systematic review of barriers and enablers to adoption and sustained use. Environ Res. 2016;146:218-234. https://www.ncbi.nlm.nih.gov/pubmed/26775003
- Paulin LM, Diette GB, Scott M, et al. Home interventions are effective at decreasing indoor nitrogen dioxide concentrations. Indoor Air. 2014;24(4):416-424. https://onlinelibrary.wiley.com/doi/full/10.1111/ina.12085
- Rice JL, Brigham E, Dineen R, et al. The feasibility of an air purifier and secondhand smoke education intervention in homes of inner city pregnant women and infants living with a smoker. Environ Res. 2018;160:524-530.
- Batterman S, Du L, Mentz G, et al. Particulate matter concentrations in residences: an intervention study evaluating stand‐alone filters and air conditioners. Indoor Air. 2012;22 (3):235-252. https://onlinelibrary.wiley.com/doi/full/10.1111/j.1600-0668.2011.00761.x
- Martins NR, Carrilho da Graça G. Impact of PM2.5 in indoor urban environments: A review. Sustain Cities Soc. 2018;42:259-275. https://www.sciencedirect.com/science/article/pii/S2210670718309272
- Hansel, Nadia N., et al. A longitudinal study of indoor nitrogen dioxide levels and respiratory symptoms in inner-city children with asthma. Environmental health perspectives. 2008;116(10):1428-1432. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2569107/