Nitrogen Dioxide Levels Decrease Due to MCO

Whilst Covid-19 continues to grip the world, storytelling through data has become increasingly important in helping people come to terms with the effects of thcrisis. 

As part of Think City’s Covid-19 response effort, the Analytics team analysed the socioeconomic health impact of the pandemic on Malaysia. Nitrogen dioxide maps were released to the public to shed some light on the positive effects of the Movement Control Oder (MCO), which began on the 18th of March 2020. Examining the nitrogen dioxide data revealed that air pollution has been falling sharply in Malaysia over the lockdown period, especially in the urban areas. 

The maps have been met with keen interest and enthusiasm, with schools reaching out to discuss the effects on climate change. 

On April 21, 2020, Think City Analytics Lead Dr Ceelia Leong participated in a digital collaborative educational event between a high school in Johor state (SMK Pasir Gudang 3) and a high school in Veszprém, Hungary (VSZC Ipari) to teach the impact of MCO on the environment. The session sparked discussions around environmental protection, and possible ways to maintain the reduction in air pollution following the end of the MCO. 

The Johorian students from Pasir Gudang felt strongly connected to the environmental cause, having recently experienced the direct health effects of heavy pollution in Sungai Kim Kim last year. Johor State Education Director Azman Adnan lauded their initiative in diversifying learning approach on environment issues.

It was a productive session fuelled by interesting questions, some of which are outlined below and answered by Dr Leong: 

Varsha: “What led you to do research on the release of nitrogen dioxide levels in Malaysia?”

C: As part of our effort to contribute in the fight against Covid-19, we wanted to map the resilience of communities in Malaysia to help decision-makers respond to the crisis and help vulnerable groups. When looking at the different ways Covid-19 will impact us, we noticed a gap in the data regarding air pollution in Malaysia. To fill this gap, we looked at nitrogen dioxide levels to gauge how it will affect the country’s public health and environment.  

Theges: “Did your research only cover nitrogen dioxide? What about other emissions like carbon monoxide and sulphur dioxide?”

C: We looked at other air pollutants, including carbon monoxide and sulphur dioxide. Carbon monoxide emitted fell during MCO, as well as sulphur dioxide. However, we chose to focus on nitrogen dioxide as it had the most pronounced change. We also observed that the air quality index has improved, largely because of nitrogen dioxide 

Affiq: “What is the most effective way of maintaining this low emission situation after MCO, as people may go back to their daily routine?”

C: There is certainly a risk that emissions will rise post-MCO, especially as people may choose to take private vehicles over public transport as a means of maintaining physical distancing. A way to reduce the effect of this is to encourage greener alternatives, such as walking and cycling, for shorter trips 

Cities could also re-design to ensure emissions stay low. For example, Milan is using the pandemic as an opportunity to reduce traffic and pollution by increasing cycle lanes in the city and expanding pedestrian pavements.  

Qeba: “We see that the west coast of Malaysia, Lombardy of Italy, and Hubei Province of China are more polluted and have recorded higher number of Covid-19 victims. Is bad air quality related to the number of covid-19 victims?”

C: Living in a polluted area for a long-period or inhaling a large concentration of pollutants in a short amount of time can affect your lungs and breathing children and those with pre-existing lung conditions can be particularly affected 1.  

Presently, there is not enough evidence to confirm a direct relationship, but some initial research has found potential links between areas with high concentrations of pollution and Covid-19 death rates, as well as links that it exacerbates Covid-19. Research on the topic is ongoing. 

Bella: “Why has climate change not gained as much as attention as Covid-19? 

C: There are few of the reasons as to why Covid-19 has drawn more attentionFirstly, the effects of climate change increase slowly and over a long period of time, making it difficult for people to see its impact. In comparison, the Covid-19 outbreak spread quickly, with people getting infected and dying around the world in short span of timeThis forced countries around the world to act with greater urgency. Secondly, the style of journalism on climate change has also made it difficult for people to relate to it, such as pictures of polar bears on melting ice capsHowever, this has started to change with more relatable images being used of people being affected by climate change, like the Australian wildfires. This topic was explored in a Think City webinar, which was held over our Earth Day campaign.  


The inquisitive dialogue initiated by the students reflect the growing environmental awareness amongst younger generations, who hope to live in a cleaner world. Their desire to learn more about nitrogen dioxide levels after seeing the map reveals the importance of data visualisation as a tool to catalyse change and stimulate debate. 

Representing data with clear imagery can also provide valuable evidenced-based insights for policymakers, industry leaders, and researchers to think about how to manage the longer-term impact of the crisis. 

Beyond this engagement, the Analytics team has also taken a closer look at the maps to offer additional insight into nitrogen dioxide levels around Malaysia during MCO. 

Nitrogen dioxide is emitted from vehicle exhaust and the burning of fossil fuels such as coal, oil, diesel fuel, and natural gas. Nitrogen dioxide and particulate matter are linked to lung diseases such as asthma and are especially harmful to children, damaging lung tissue and reducing lung function.  

These maps, produced using satellite spectrometry data, compare one-year satellite observation data (Sentinel 5-P) over the MCO period in 2020 with the same period in 2019. They indicate that the drops in nitrogen dioxide levels are most noticeable in urban areas such as Kuala Lumpur and Johor Bahru, and along major transportation corridors. On the other hand, nitrogen dioxide levels are consistently low in East Malaysia. The reduction in its levels in Malaysia can be directly attributed to fewer people using motor vehicles.

Previously, nitrogen dioxide levels in the Klang Valley area were very high due to the density of human population and urban activity. But with the MCO, most Malaysians are forced to stay home and avoid outdoor activities, which is reflected in the reduction of the air pollution in the maps below. 2

Similar patterns can also be seen in Europe, China and the USA 

Think City programme director Dr. Matt Benson mentioned that these positive environment impacts are an unintended consequence of Malaysians being less mobile and being forced indoors.  

“As we are forced into hibernation, our cities are changing in ways we hadn’t thought possible. Our mapping of changes in nitrogen dioxide between now and this time last year shows that as Malaysians move about less due to the MCO, there are reduced vehicle emissions. This is particularly evident along the west coast of Peninsular Malaysia, which is where 20 million people reside. What we have learnt is that is our collective behaviour contributes to pollution, so we have a collective responsibility to reduce it post-MCO.” he said. 

Dr. Benson added that data is a key weapon in combating the Covid-19 crisis as it would help policymakers respond to the social and economic impacts of the pandemic. 

“Not only will data help manage the disease itself but also help us keep track of, and even plan ahead of, the social and economic consequences. We also need to engage a range of institutions. One example is the collaboration with high schools in Hungary and Johor to raise awareness on air pollution based on the nitrogen dioxide emission maps. he said. 

Dr. Leong added that the team was compiling up-to-date data ranging across areas, to be analysed and incorporated into policy responses.  

“For the rest of the MCO and beyond, we will continue to use data mapping tools which we have developed in-house, to offer even further insights on the impact of Covid-19 on Malaysia — how people are faring and which places or groups require attention and action.”  

Devoid of vehicles and crowds, an unusual silence descends upon KL’s core. Image source: Kenny Loh.

In addition to the nitrogen dioxide maps, Think City has developed ‘The Covid-19 Community Resilience’ tool to visualise data – developing easy, interactive, and publicly-accessible maps that highlight the places and communities most vulnerable to the current and potential impacts of Covid-19 in Malaysia. This tool can help users understand the complexity of impacts by overlapping different socio-economic and health data to assess areas of higher vulnerability and identify under-supported communities. The Covid-19 Community Resilience mapping tool is available online via Think City’s Urban Analytics webpage.


1  The air pollutant guidelines by WHO state that just 1 hour of exposure to nitrogen dioxide exceeding 200 µg/m3 is considered toxic, with even long-term exposure to lower concentrations resulting in adverse health outcomes. For instance, an increase in annual nitrogen dioxide concentrations is correlated with an increase in bronchitis symptoms of asthmatic children. The current WHO guideline value of 40 µg/m3 (annual average) was set to protect the public from the health effects of gaseous nitrogen dioxide.

2 Think City’s nitrogen dioxide mapping of Peninsular Malaysia is a measure of volume and density across a spectrum. The highest nitrogen dioxide emission in 2019 at that end of the spectrum was 315.4 micromole/m2 and in 2020, the highest is 244.6 micromole/m2, a difference of 40.8 micromole/m2 or 12.9% change. The decrease percentage is close to 50% if it is looked by the upper end of the spectrum (volume above 150 micromole/m2).