How NOx and SO2 Harm Health

Co-Pollutants Released with CO2 Harm Health Laser Talk

Fossil-fuel-fired power plants and vehicles together account for about 70% of total CO2 emissions in the U.S.[1] Along with CO2, these sources also release the co-pollutants sulfur dioxide (SO2) and nitrogen oxides (NOx) that harm health.

Breathing either sulfur dioxide (SO2) or nitrogen oxides (NOx) for short periods (24 hrs or less) can cause adverse respiratory effects such as airway inflammation, bronchoconstriction, asthma symptoms, emergency department visits and hospital admissions, especially for those with asthma or respiratory illnesses [2].

Both SO2 and NOx also harm health by reacting in the atmosphere to form sulfate or nitrate fine (small) particles (PM2.5), respectively [2]. These PM2.5 particles are microscopic solids or liquid droplets that are so small they penetrate deeply into the lung and harm health. About 50% (OR about one-half) of total PM2.5 in the air is formed from SO2 and NOx. Most of the rest of PM2.5 is formed from carbon released from vehicles, industry, forest fires, and biogenic sources such as trees.) [3]

A study estimated PM2.5 levels in the year 2005 caused [4]:

  • 83,000 cases of bronchitis
  • 200,000 hospital admissions and emergency room visits for respiratory, cardiovascular or acute asthma symptoms
  • 2.5 million asthma exacerbations
  • 4.4 million cases of upper or lower respiratory symptoms
  • 18 million lost days of work
  • between 130,000 and 320,000 premature deaths

Nitrogen oxides (NOx) also harm health because they are major precursors to ground-level ozone. Ozone is not emitted directly into air but is created by chemical reactions between NOx (released from burning fossil fuels) and other volatile chemicals in the air in the presence of sunlight. Breathing ozone can cause a variety of adverse health effects including chest pain, coughing, throat irritation, and congestion. Ozone can worsen bronchitis, emphysema and asthma; reduce lung function and inflame the lining of the lungs; and, even cause premature death [5]. NOx is the most important pollutant essential to forming ozone.)

A study estimated ozone levels in the year 2005 caused [4]:

  • 77,000 hospital admissions and emergency room visits
  • 29 million days requiring restricted activity
  • 11 million school absence days
  • between 4,7000 and 19,000 premature deaths

Skeptic Claims and One-Liners

Carbon Fee Skeptic Claim: Why are NOx and SO2 bad for health?
One-Liner: Together, NOx and SO2 account for about half of PM2.5, and NOx is the most important pollutant essential to forming ground-level ozone.

  1. “Overview of Greenhouse Gases”. U.S. Environmental Protection Agency. Last Updated: 5/7/2015.
  2. “What Are The Six Common Air Pollutants?”. U.S. Environmental Protection Agency. Last accessed: 5-15-15. URL for SO2. URL for NOx.
  3. “Understanding Particle Pollution”. U.S. Environmental Protection Agency. December, 2004. EPA 454-R-04-002.
  4. Fann N, Lamson AD; Anenberg SC, Wesson K, Risley D and Hubbell BJ. 2011. Estimating the National Public Health Burden Associated with Exposure to Ambient PM2.5 and Ozone. Risk Analysis 32(1):81-95.
  5. “Ground Level Ozone: Health Effects”. U.S. Environmental Protection Agency.” Last updated: 11/26/14. URL: