Block ip Trap

We Can See Clearly Now: How the COVID-19 global quarantine has impacted air quality

15 May 2020

By Shaina Shay

The COVID-19 pandemic has impacted nearly every person on the planet. Working remotely, living under quarantine, caring for someone infected - everyday life has fundamentally changed. But how has this global quarantine behavior impacted the world as a whole? 

The environment has quickly adjusted to its humans moving indoors, reducing travel, and slowing production of non-critical consumer goods, and the results have been nothing short of astonishing. Waters have cleared, animals have returned, and air quality has improved. 

It comes as no surprise that much of the improvement in air quality can be attributed to an extreme reduction in fossil fuel emissions. Levels of both nitrogen dioxide (NO2) and particulate matter declined during the early months of the pandemic. Of these two pollutants, however, it’s NO2 that experienced the most significant change. To better understand the impacts, let’s take a look at the facts. 

Nitrogen Dioxide

NO2 is a closely-monitored pollutant that can irritate respiratory systems, aggravate existing health conditions (like asthma and COPD), and has been shown to contribute to the development of lung diseases from long term exposure. The primary source of this pollutant is combustion of fossil fuels (e.g. emissions from coal smokestacks and automobiles). NO2 concentration has a significant impact on general air quality because it, along with other oxides of nitrogen (NOx), can interact with chemicals in the atmosphere to create new respiratory irritants like particulate matter (PM10 and PM2.5) and ozone. 

Due to their adverse effect on the environment, NOlevels have been closely monitored by a team of government agencies. One agency tasked with this assignment, the US EPA, created an air quality guide for NOthat includes a rating system with public recommendations. The EPA determined these critical thresholds:

  • 1-hour NO2 standard at the level of 100ppb and;
  • Annual average NO2 standard of 53 ppb. 

To maintain regulatory compliance, state and local agencies are responsible for monitoring and reporting NO2 levels to the EPA throughout the year. In addition to on-the-ground monitoring, NASA and other international agencies, like the European Space Agency (ESA), monitor concentrations of NO2 from space. The Sentinel-5 Precursor (Sentinel-5P) is an ESA satellite dedicated to monitoring a wide variety of air pollutants. The troposphere is the layer of air closest to the earth, where we breathe our oxygen and experience our weather. Preliminary analyses of tropospheric NO2 data from Sentinel-5P show a drastic decrease of the amount of NO2 between January and March 2020, when compared to previous years. The decrease corresponds with the COVID-19 quarantine measures across the globe, and the subsequent “powering down” of our daily activities. Given the extraordinarily high levels of pollution its citizens have endured over the past several years, it comes as no surprise that the region with the biggest change in NO2 levels has been China, where the most severe quarantine measures were first imposed. As parts of Europe adopted quarantine measures, the NO2 levels over that area followed a similar decline.

According to ESA, a more detailed quantitative analysis of the impact of quarantine measures is underway (using ground data, weather data and inverse modelling), but will likely take some time to complete. 

 Figure 1 Europe

Figure 1 shows data from France and Italy comparing NO2 levels for March 2019 to March 2020. 

Figure 2 China

Figure 2 shows the short-term changes in NOlevels across China before quarantine (January), during strict quarantine (February), and after quarantine restrictions were lessened (March). It is common for NO2 levels in China and much of Asia to decrease during the Lunar New Year celebrations (January 28th - February 9th) due to reduced human inactivity. This year however, the levels have decreased more significantly and stayed lowered for longer compared to previous years. In the major Chinese cities the ESA estimated that NO2 levels were reduced by nearly 40 percent. 

A Breath of Fresh Air

We’ve witnessed impressive reductions in air pollution levels in the first few months of 2020. But these short-term air quality improvements are unlikely to be maintained if our behaviors do not change as the global economy reboots. Even now, as quarantine measures lessen in China, NO2 levels are beginning to rebound. 

Policy decisions in the near future can push our air quality in either direction. On March 26th 2020, the US EPAannounced an unprecedented temporary policy that halts enforcement of environmental regulatory compliance, citing COVID-19 as the catalyst for this decision. While there are built in safeguards (e.g. continued documentation requirements and discretionary enforcement clauses), the long-term consequences are unknown.  

This is a pivotal moment. Governments, industry, and individuals have a unique opportunity to choose how we react to our new and changing world. If there is one thing we have learned from global quarantine, it’s that large-scale changes can happen, and they can happen fast. Imagine if air quality and environmental health were integral in the development of government relief packages. Let’s realize the combined power of our individual travel and purchase choices. Let’s take in this global breath of fresh air, and help the future breathe a little easier.  


Shaina Shay is the Environmental Market Manager at Alicat Scientific. Shaina is a policy development and research expert, specializing in environmental resource management. She has led campaigns resulting in smart, sustainable policies around the world.

Alicat Scientific |

Author: Shaina Shay
Volume: 2020 May/June