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Large-scale study associates even brief exposure to PM2.5 with childhood lung infections

Even the briefest increase in airborne PM2.5 is associated with the development of acute lower respiratory infection (ALRI) in young children, according to a new, large-scale study published in the American Journal of Respiratory and Critical Care Medicine, an American Thoracic Society journal. Increases in PM2.5 levels also led to increased doctor visits for these lung infections.

The study is the largest to date on this health concern, involving more than 100,000 patients. The research was undertaken by a team from Intermountain Healthcare, Brigham Young University, and the University of Utah.

The most important finding of this study is that infectious processes of respiratory disease may be influenced by particulate matter pollution at various levels. The exact biological implications of the study’s findings require further investigation.

—lead author Benjamin Horne, PhD, director of cardiovascular and genetic epidemiology at the Intermountain Medical Center Heart Institute

Dr. Horne and colleagues studied 146,397 individuals who were treated for ALRI between 1999 and 2016 at Intermountain Healthcare facilities throughout Utah’s Wasatch Front region.

The Wasatch Front is approximately 80 miles long and 10-20 miles wide, bordered on both sides by mountains. It consists primarily of suburbs, but also includes the cities of Salt Lake City, Ogden and Provo/Orem.

PM2.5 levels were estimated based on data from air quality monitoring stations along the Wasatch Front, where approximately 80% of Utah’s population resides. Measurements were also made at secondary locations. Short-term periods of PM2.5 elevation were matched with the timing of increases in healthcare visits for ALRI.

The primary aim of the study was to determine if there was an association between these fine particulates and ALRI in very young children, with a secondary objective of finding the same associations for older children, adolescents and adults.

Approximately 77% (n=112,467) of subjects were 0-2 years of age. The odds of ALRI encounter for these young children increased within 1 week of elevated PM2.5 and peaked after 3 weeks with a cumulative 28-day OR= 1.15 per +10 μg/m3 (95% CI=1.12, 1.19). ALRI encounters with diagnosed and laboratory-confirmed RSV and influenza increased following elevated ambient PM2.5 levels. Similar elevated odds for ALRI were also observed for older children, although the number of events and precision of estimates were much lower.

—Horne et al.

Nearly 60% of US children live in counties with PM2.5 concentrations above air quality standards.

This study was performed in a location where the average daily PM2.5 level is lower than places like Los Angeles and New York. Due to the topography of the region, though, air pollution may become trapped in the high mountain valleys of the Wasatch Front—especially during temperature inversions, which typically occur in the winter months.

When PM2.5 becomes trapped in the valleys, this often leads to sharp increases in PM2.5 to levels considered to be unhealthy (>35 micrograms per cubic meter, and at times approaching 100 µg/m3).

In many places that have higher average PM2.5, the PM2.5 level does not vary as much as it does on the Wasatch Front, so it is not clear how this study’s findings may transfer to those locales where the air pollution exposure is higher over the long term, but short term spikes do not occur. It may be, though, that long-term exposure to air pollution makes people more susceptible to ALRI on a routine basis, although additional studies will be required to test this hypothesis.

—Dr. Horne

Bronchiolitis, a condition in which small breathing tubes in the lungs called bronchioles become infected and clogged with mucus, is the most common acute lower respiratory infection in children.

Fifty to ninety percent of bronchiolitis cases are caused by respiratory syncytial virus (RSV), which is the most common cause of hospitalization in the first two years of life. Sixty-four percent of individuals studied had a diagnosis of bronchiolitis.

Overall, it took about 2-3 weeks for the ALRI hospitalizations or clinic visits to occur in this study after the rapid rise in PM2.5 had been observed.

—Dr. Horne

In an analysis of death rates among the study population, 17 children ages 0-2, nine children ages 3-17 and 81 adults (18+) died within 30 days of diagnosis with ALRI.

The air pollution itself may make the human body more susceptible to infection or may impair the body’s ability to fight off the infectious agents. It may be that PM2.5 causes damage to the airway so that a virus can successfully cause an infection or that PM2.5 impairs the immune response so that the body mounts a less effective response in fighting off the infection. This could lead to longer periods of ALRI symptoms or more severe symptoms requiring a higher intensity of medical care for the infected individual. It may also be that periods of acute increases in PM2.5 lead people to stay indoors more where they are in closer contact with others who carry infectious agents and can transmit the infection to them.

—Dr. Horne

Motor vehicles contribute about 48% of emissions that lead to the formation of fine particulates. Small industry and businesses such as gas stations and dry cleaners, as well as home heating, emit about 39% of all fine particulates. Large manufacturing accounts for 13% of fine particulates.

The practical implications for prevention of ALRI and amelioration of symptoms include that when an acute increase in the level of PM2.5 occurs, people may be able to prevent infections or decrease ALRI symptom severity or duration by reducing their exposure to the air pollution.

Furthermore, a substantial elevation in PM2.5 may also serve as a nudge that reminds or alerts people to avoid areas and activities where other people may share an infection with them, to not touch their face with dirty hands, to be vigilant about washing their hands when reasonably possible or prudent, and to engage in other preventive behaviors that are known to reduce infection risk.

—Dr. Horne


  • Benjamin D. Horne, Elizabeth A Joy, Michelle G Hofmann, Per H Gesteland, John B Cannon, Jacob S Lefler, Denitza P Blagev, E. Kent Korgenski, Natalie Torosyan, Grant I Hansen, David Kartchner, C. Arden Pope III (2018) “Short-term Elevation of Fine Particulate Matter Air Pollution and Acute Lower Respiratory Infection” American Journal of Respiratory and Critical Care Medicine doi: 10.1164/rccm.201709-1883OC



Another very good reason why we should stop burning fossil and bio fuels?


Harvey, we could also use diesel cars with DPF that reduce PM2,5 levels (tailpipe PM2,5 is lower than ambient PM2,5), something that electric cars can never do.


Gasoline with GPF is also good. However, I would at this point hesitate to say that it would decrease particulate emissions compared to ambient levels. Results in the literature show great variation in GPF efficiency and not quite the low levels we see with diesel+DPF.


Diesel and other liquid fuel vehicle manufacturers will continue to cheat and we (the users) will continue to harm and kill our children and all living creatures as long as we haven't made the transition to clean electrified vehicles.

The installation of more clean REs and manufacturing of improved electrified vehicles should be accelerated.

China is the leader with 500,000+ new electric trucks and buses and over 55% of the world EVs. .


Cheating on emissions certification of conventional vehicles is now essentially impossible in the U.S./Canada. The regulators are now taking as much as 6 months longer to certify light-duty diesel vehicles due to all of the rigorous extra testing that's being done, including real-world driving using PEMS under a myriad of ambient conditions.


Harvey, PN emissions from diesel cars are more than a factor of 10 lower than the legislative limits, sometimes up to 100 times lower. This is why these cars clean the air, a fact that has not been recognized by media. If you need to know more, just look in the February issue of the German Journal MTX.

A DPF is "digital", either it works or it is broke. If it breaks, the engine ECU will detect it and the "check engine" lamp will light up. Eventually, the DPF durability is very good, so not even this is an issue. The problem we have is instead with GDI gasoline cars that emit 10-100 times more nanoparticles than DPF diesels.

Harvey, I think I have explained all this to you now at least 10 times but you still do not comprehend. Why?


I admit the new diesels are cleaner than old units but if we could continuously (really) clean the air driving polluting diesels, people would quickly return to diesel vehicles instead of racing to gasoline-electricity-H2 vehicles?

We were driving behind a brand new Nova diesel city bus yesterday and we had to close all air intakes, even if our new car is equipped with Hopa filters?


@Harvey - not sure what you smelled from the Nova bus, but there's an actual demonstration by Dr. Bruce Hill of Clean Air Task Force of a diesel school bus retrofitted with DPF emitting "1/60th of what's in the outdoor air that we're breathing right now." In other words, it's filtering the ambient air of particles. @3:32-3:58 mark

Just to be clear, CATF is an environmental activist group and is NOT a supporter of diesel engine technology.


Well, we may find that diesels emit many other types of smelly solutions. How harmful are they, remains to be evaluated?


That's already been addressed, Harvey.

The "Advanced Collaborative Emissions Study" (ACES) looked at over 300 unregulated emissions from three 2007-compliant diesel truck engines (Phase 1) and three 2010-compliant diesel truck engines (Phase 2). The results...

"...Unregulated emissions that included single ring aromatics, PAH, nitroPAH, alkanes, alcohol and organic acids, hopanes/steranes, carbonyls, metals and elements, organic carbon, elemental carbon, and dioxins/furans were 79 to 99 percent lower than the emissions from a similar 2004 technology engine...." "Advanced Collaborative Emissions Study (ACES) Phase 1 Final Report." June 2009 (Page 83)

"...Unregulated emissions that included single ring aromatics, PAH, oxyPAH, nitroPAH, alkanes, alcohol and organic acids, hopanes/steranes, carbonyls, metals and elements, organic carbon, elemental carbon, dioxins and furans were 50% to 99% percent lower than those emitted from 2007 technology engines tested in ACES Phase 1...." "Phase 2 of the Advanced Collaborative Emissions Study - Final Report." November 2013 (Page 69 of 70)

Phase 3 of ACES looked at health effects of diesel exhaust by exposing laboratory mice and rats to concentrated diesel exhaust from a 2007-compliant diesel truck engine. The animals showed to ill-effects of the exposure - (Slide #19)


How clean were those compliant diesel trucks/buses after 100,000, 250,0000 and 500,000++ miles and also at idling, on acceleration and for the first few miles (in the morning).

Of course those stats are never published but most drivers and bikers can confirm the present of smelly smoke?

A quick stop as at bus/truck stop will also confirm same.


If you look at the studies, a special more realistic duty cycle was developed especially for these studies.

I have two diesel vehicles, neither one of which smoke or have any exhaust smell whatsoever. There are still many legacy diesel vehicles (pre-2007) on the road and it's not always easy to know if they are new-technology diesel engines.


If new diesels operate that clean, why so many buyers/users in EU and USA are progressively and quickly moving away.

Sales of HEVs, PHEVs, BEVs and FCEVs could become the favored replacements?

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