Air pollution decrease in India during COVID-19 lockdown not as high as originally thought
Researchers find meteorology played an important and unaccounted role


Date:
November 16, 2021
Source:
York University
Summary:
Observational data shows air pollution in India decreased
drastically in the first COVID-19 lockdown when emissions from
vehicles naturally declined, but researchers say those numbers only
tell part of the story - - blue skies and an absence of visible
smog can be deceiving and hide pollutants that could potentially
cause health issues.



FULL STORY ========================================================================== Observational data shows air pollution in India decreased drastically
in the first COVID-19 lockdown when emissions from vehicles naturally
declined, but York University researchers say those numbers only tell
part of the story - - blue skies and an absence of visible smog can be deceiving and hide pollutants that could potentially cause health issues.


==========================================================================
Air pollution results from a complex mix of interactions between
emissions, meteorology, such as wind direction and rain, as well as
chemistry, but looking only at observational data as many recent studies
have done without take meteorology into account, skews the numbers.

The researchers found that some air pollutants didn't drop nearly as much
as first thought and even more surprising was that ozone levels increased
even as other pollutants decreased. The air looked much cleaner, but that allowed more sunshine to get through, creating conditions for ozone (O3)
to increase up to 30 per cent.

"To accurately quantify the impact of the COVID-19 lockdown on air
pollutant levels, meteorology and atmospheric chemistry needs to be
considered in addition to emissions," says York University postdoctoral researcher Leigh Crilley, who led the Faculty of Science research along
with York Associate Professor Cora Young and team. "Our research shows
the decline in local emissions had less influence on the decrease
in air pollutants than first thought." As the national lockdown in
India reduced major urban sources of air pollution, such as traffic,
industry and construction, it gave the researchers an opportunity to
study the contribution of local sources of air pollutants during normal meteorological conditions.

To get a clearer picture of potential decreases in air pollution, Crilley
and Young focussed their study on nitrogen oxides (NOx), fine particulate matter (PM2.5) and O3, as well as what was happening meteorologically at multiple locations within two cities in India -- Delhi and Hyderabad --
during the start of the first lockdown, from March 24 to April 24, 2020.



==========================================================================
Air pollution is a known health risk and India has some of the worst
air pollution globally resulting in a disproportionally high level of
mortality and disease. It is estimated that air pollution exposure, particularly PM2.5, resulted in the death of 1.27 million people in 2017.

Cities in India also have some of the highest O3 levels in the world,
which can be formed from a complexity of sources and chemistry, either NOx-limited or volatile organic compounds (VOC)-limited.

The researchers used hourly data from air quality monitoring stations
for levels of PM2.5, NOx and O3, and hourly meteorological and visibility
data.

They compared that data to the same dates from the previous three years
to evaluate changes due to the lockdown. A boosted regression tree model
was built to account for the influence of meteorology on observed levels.

When only taking observational data into account, NOx and PM2.5fell by
up to 57 per cent and 75 per cent respectively, but when meteorology
was factored in, those percentages fell to less than eight per cent for PM2.5and between five and 30 per cent in both cities, while O3increased.

They found that local sources of emissions, such as vehicles and the
burning of fuels, had less influence on air pollution levels than regional emissions sources, while weather events and atmospheric chemical processes contributed independently to air pollutant levels.

"We demonstrate that regional sources, such as rural and agriculturally
based emissions, that may have been less affected by the lockdown, have
a significant influence on PM2.5levels in Delhi and Hyderabad after weather-normalization.

This indicates that future PM2.5mitigation strategies should focus on
national- scale, as well as local sources," says Young.

"Overall, this study highlights the impact of emissions, meteorology and chemistry on air pollution and that all three should be considered when assessing the effects of any short-term intervention on air pollutants."
In addition, the research team found that ozone production in Delhi is
likely VOC-limited and, as such, attempts to mitigate it should focus
on dominant VOC sources.

The researchers say this really points to the need regulators to
understand the complex factors involved in air pollution if they are
going to make policies to reduce pollutants and ozone.

========================================================================== Story Source: Materials provided by York_University. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. Leigh R. Crilley, Yashar E. Iranpour, Cora J. Young. Importance of
meteorology and chemistry in determining air pollutant levels
during COVID-19 lockdown in Indian cities. Environmental Science:
Processes & Impacts, 2021; DOI: 10.1039/D1EM00187F ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/11/211116111318.htm

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