Nitrogen Oxides

Nitrogen Oxides

NOx, or Nitrogen Oxides

How can you measure an invisible, odorless gas? Increasingly, the answer is to use satellites. New satellites are being used to detect emissions of pollution like methane, CO2, and other gases, including NOx (nitrogen oxides). These satellites can even be used to track emissions from the smokestacks of ships, revealing plumes of pollution across our oceans and across port towns.

NOx, or nitrogen oxides, are primarily released by burning fossil fuels. Urban areas tend to have higher levels of NOx from widespread emissions from cars, buses, and trucks. However, industrial sources like power plants and flares are also significant sources of NOx emissions in rural areas. Marine shipping is responsible for about 15% of all NOx emissions from human activities. 2024 data from LDEQ shows that in St. James Parish, 2005 tons of NOx were released from industrial sources. Ascension Parish had more than triple the emissions of NOx at 6630 tons, while St. John was more than double at 4265. St. Charles has the second-highest industrial NOx emissions in the state at nearly 14,000 tons.

During childhood, exposure to even low levels of NOx can cause permanent damage to the lungs, leading to the development of asthma. Adults and children with asthma who are exposed to NOx can have an asthma attack. People without asthma can experience shortness of breath, cough, lung damage, and increased risk of respiratory infections. Symptoms are usually worse one to two days after exposure. A 2024 study used satellite NOx measurements to show that when NOx levels increase, so do hospitalizations in Cancer Alley for asthma. Furthermore, the study found that areas with high NOx emissions are overwhelmingly Black communities. About 1 in 10 people in Louisiana have asthma, and NOx emissions are a large concern for this vulnerable community. 

NOx emissions from power plants have greatly reduced in the past 40 years, but are still present at levels which can cause serious harm. NOx is released from car exhaust, power plant emissions, natural gas stoves, and improperly burned natural gas in flares. When NOx interacts with air, VOCs, and UV light from sunlight, it releases an oxygen atom, which bonds with two other oxygen atoms to form ozone, or O3. It also breaks down into molecules that become PM 2.5. NOx reacts with water and oxygen to cause acid rain. Exposure to all three chemicals causes complex effects in the human body as well. The complex relationship between NOx, ozone, and PM2.5 means that reducing NOx emissions has widespread effects on other pollutants. 

Diesel engines, like those used on ships, are large emitters of NOx. Although there are several global treaties and controls to prevent NOx emissions, emissions have not greatly decreased. Worldwide, however, there have been successful efforts to reduce NOx emissions from ships and vehicles at ports. Policies that do not allow ships to idle their engines while in port and electrification of port vehicles have resulted in reductions of NOx pollution between 60-85%, with millions of dollars in public health benefits from the reduced pollution. The solution to eliminating all marine NOx emissions will not be simple. Although ammonia is being proposed as a new shipping fuel to replace fossil fuels, it releases NOx when combusted in engines. Newer engines are more effective and can be retrofitted into some older ships, but even the most efficient fossil fuel-powered engines still release some NOx. 

In 2025, RISE developed its Clean Ports Report Card for the Port of New Orleans along with our partners at Friends of the Earth and Better World Group. We found that the Port needs serious improvements in transparency and emissions reductions. With over 80% of international trade carried by sea, shipping isn’t going anywhere. It will be up to scientists, ports, ship operators, and international marine organizations to come up with the solutions to make shipping part of a zero emissions world. 

See our Clean Ports Report Card here: https://assets.ctfassets.net/aafuy6bw3szy/1ZLY3N9piVmMMqv9SSIomc/24953c2055511d54351f4ff54e923333/NOLA_Clean_Ports_Report_Card.pdf 

HOW TO REDUCE YOUR EXPOSURE TO NOX

  • NOx emissions are often highest during rush hour. If you or your children have asthma, avoid going outside during these hours. NOx does clear from the air quickly, so levels reduce after the traffic slows down.
  • NOx emissions from methane (natural gas) stoves are responsible for over 10% of childhood asthma cases. Switching to electric or induction eliminates the NOx; using a vent hood and using the back burners can greatly reduce NOx exposure. If you rent, many states and cities require vent hoods to be installed. 
  • If you live near areas with heavy traffic, consider installing an air purifier in the rooms where you and your children spend the most time. 
  • You can see almost real-time NOx for the US on this NASA satellite https://tempo.si.edu/data_for_public.html  and see worldwide emissions from this satellite https://svs.gsfc.nasa.gov/5154/