Global Clean Air

Breathe London Data Reveals Big Drops In NO2 Pollution During Commuting Hours

By Catherine Ittner / Published: October 19, 2020

London businesses are starting to reopen and some nonessential workers, who have been working from home, are considering going back into their offices. But what impact might this have on air quality?

During the lockdown, air quality data from Breathe London shows that harmful nitrogen dioxide (NO2) pollution went down significantly during commute times – 25% in the morning and 34% in the evening.

To help maintain these lower levels of pollution as shops and offices begin to reopen, businesses should allow more flexible ways of working. A new survey confirms it’s what people want.

BL weekday covid

Less pollution during commute times

Before the lockdown, many people across the city followed similar schedules on weekdays. As a result, the Breathe London network of air pollution sensors often saw daily dips and peaks of NO2 – a gas produced by fossil-fuel combustion that is associated with heart and lung-related health impacts.

In the pre-lockdown patterns, the lowest levels of this pollution measured was in the wee hours of the morning (around 3-4 am), when most people are sleeping. After they wake up and start moving to school and work, many in their fossil-fuel powered vehicles, the monitors saw a pronounced pollution increase. This falls midday, but pollution rises again in the evening to a second spike as folks return to their homes.

After confinement measures went into place, Breathe London data shows that air pollution significantly decreased across the city, including in residential areas, indicating there have been benefits to Londoners’ health even away from busy roads.

To get a better sense of how lockdown and many people working from home was impacting air quality, we then zoomed in on weekday commuting hours. Across Greater London, NO2 pollution decreased around 25% during the morning commute (8-11am) and 34% in the evening (5-8pm). These pollution reductions were even greater in the city centre, where many businesses are located – 31% and 37% respectively in the Ultra Low Emission Zone.

More work flexibility and clean air action

As lockdown eases, people across the UK want more flexible working options and action to lower air pollution.

That’s the gist of a new survey, commissioned by charity Global Action Plan on behalf of Business Clean Air Taskforce, which finds that:

  • 87% of those currently working from home would like to continue to do so to some degree.
  • 72% of the public believe clean air is more important now because coronavirus can affect people’s lungs.
  • 74% want businesses to do more to improve air quality in the recovery.

Not everyone can work from home, so it’s important businesses provide the option for those who can – leaving the roads and public transport available for essential workers to travel safely.

Build back better

Data helps us understand how pollution changes across the city, and Breathe London data shows the confinement measures have helped lessen the pollution peaks typically associated with commuting.

To protect public health and prevent the return of higher pre-lockdown pollution levels, UK employers should build back better and give people what they want by offering more flexible work options.

For more information on how pollution levels changed since confinement measures went into place, please see the full Breathe London analysis.

This was originally posted to EDF Europe.

Also posted in London, UK / Authors: / Comments are closed

Digging deeper into London air pollution reduction with Waze

By Anne Marie Borrego / Published: June 23, 2020

Editor’s Note: Today’s post is by Meg Dupuy-Todd, a Manager at Environmental Defense Fund. Meg has led projects as a part of EDF’s Global Clean Air initiative, including collaborations with Google’s Project Air View in London and Salt Lake City.

Covid-19 has disrupted everyone’s lives, including providing an unfortunate and unwelcome experiment to examine London’s changing commuting and pollution patterns.

At Environmental Defense Fund, we have been collecting air quality data as part of Breathe London, a collaborative project to map and measure pollution in London. We could see that the social distancing measures had changed nitrogen dioxide (NO2) pollution levels, but we wanted to provide a fuller picture and determine what factors might be at play, including traffic.

Here’s how we used Waze for Cities data to dig deeper into the cause of observed NO2 pollution reductions.

NO2 pollution changes

The Breathe London consortium, with partners including Google Earth Outreach, has collected hyperlocal data to help Londoners better understand pollution in the city. Displayed in real-time on an interactive map, the Breathe London project measures and displays data from air quality sensors across the city.

After social distancing was strongly encouraged in the city in mid-March, the Breathe London monitors saw substantial NO2 pollution reductions — across the full network and especially in the city’s Ultra Low Emission Zone (ULEZ) in Central London. The greatest reductions occurred during daytime hours, between 6:00–22:00, when we also expected traffic to be the highest.

FIGURE 1: Breathe London network hourly mean NO2 measurements during 17 March to 13 April 2020 compared to pre-confinement levels.

FIGURE 1: Breathe London network hourly mean NO2 measurements during 17 March to 13 April 2020 compared to pre-confinement levels.

Exploring Waze data

It was a given that restrictions to help reduce the spread of Covid-19 would change traffic patterns, as workplaces and businesses closed and many people began to work from home. As road transport is a major source of NO2 pollution, naturally, our assumption was there was a link with fewer vehicles on the road.

Through partnership with Waze for Cities program, we had access to Waze-generated anonymous incident and slow-down information in Greater London. Could the data help us understand where and how traffic had reduced?

From previous reviews of Waze data, we knew it would not provide us direct information on traffic volume — the number of vehicles on the road. Instead, we relied on the reported congestion information comparing speed on roads as compared to free-flow traffic. Using Google BigQuery, we were able to analyze the large volume of spatio-temporally resolved data to begin to get a picture of daily traffic congestion in London. Using two distinct geographical boundaries (Greater London and the ULEZ), we decided to calculate, for each hour of the day, the total length of roads where traffic was less than 60% of free flow speed as our proxy for traffic.

With our analysis, we saw that traffic congestion reduced to such an extent that it was approaching free-flow in the vast majority of Greater London roads after the stay-at-home order, even during what used to be peak commuting hours. This is most pronounced in the mostly commercial ULEZ.

FIGURE 2: Waze data — mean total length of congested roads by hour during 17 March to 13 April 2020 compared to pre-confinement levels. (Note difference in scales for Greater London and the ULEZ).

FIGURE 2: Waze data — mean total length of congested roads by hour during 17 March to 13 April 2020 compared to pre-confinement levels. (Note difference in scales for Greater London and the ULEZ).

Putting it all together

With both datasets in hand, our team was able to look at the differences over time of NO2 pollution and traffic congestion. We knew that traffic varied by day of week, so we compared the data to a pre-confinement median by day of week and hour of the day.

We found an apparent association between the reduced pollution levels and lower traffic congestion in London. Examining the daily pattern of traffic congestion also suggests a tie between the biggest drops in pollution and the biggest drops in congestion — which both occur in the late afternoon from around 3 to 7 pm. You can see this depicted in the chart below. Note the difference in “variability in road congestion due to traffic during confinement” (shown in red) and the “weekly congestion average” (shown in green).

FIGURE 3: Breathe London network NO2 measurements during 13 March to 13 April 2020 in comparison to the typical hourly pre-confinement levels.

FIGURE 3: Breathe London network NO2 measurements during 13 March to 13 April 2020 in comparison to the typical hourly pre-confinement levels.

There is still a lot more to learn about the changes in road transport emissions and the relationship to measured pollution, but by incorporating the Waze data into our Covid-19 analysis we were able to shed new light on why NO2 pollution has recently gone down in London.

To learn more about our assessment please visit BreatheLondon.org/covid19.

 

This was originally posted on Medium.

Also posted in London, Partners, Science, UK / Authors: / Comments are closed