Agricultural emissions are responsible for about half of all manmade pollution
—Catherine Elton
There’s much handwringing over the negative environmental effects of
agriculture and livestock production. But one topic that is often absent
from debates on how to sustainably feed the world is the role
agriculture plays in air pollution. As it turns out, it plays a starring
role. According to a study published recently in the journal Geophysical Research Letters, most of the air pollution over the western world is coming from agriculture.
“It was really a surprising finding,” says co-author Kostas
Tsigaridis. “Agriculture is the primary contributor of aerosol air
pollutants over extensive areas where millions of people live. I was
expecting it would be industry or even residential sources.”
Ammonia emissions on farms come from livestock waste and nitrogen
fertilizers. However, in order to form damaging aerosols, those
emissions must combine with combustion emissions. So even if we don’t
decrease agricultural ammonia emissions, but continue to reduce
combustion emissions, air quality will improve.
The presence of these aerosols in the atmosphere have serious
implications for human health. Inorganic aerosols, which are tiny
particles suspended in gas, are the main component of manmade pollution
with particulate matter smaller than 2.5 micrometers in diameter, known
as PM2.5. Particulate matter causes lung cancer and cardiopulmonary deaths.
For the study, researchers used a NASA Earth system model with a
module that tracks aerosols. This enabled them to use both climate and
emissions data to calculate aerosol pollution around the world for a
pre-industrial year (1850), current day (2010), and the future (2100).
In addition to a base run, the researchers considered two additional
scenarios, one in which all manmade emissions were set to zero, and one
in which agricultural emissions were set to zero. This way, they
could isolate three sources of pollution: natural, agricultural, and
manmade without agriculture.
For the US, the researchers found that agricultural emissions are
responsible for about half of all manmade pollution. In other words,
food production, without even taking into account processing and
transportation, is responsible for the same amount of PM2.5
as all other human activities combined. In Europe, it is responsible for
55 percent of all human activity-related air pollution.
On a positive note, the researchers found that by the end of the century, PM2.5
from manmade sources is set to decline—even though agricultural ammonia
emissions could double by then. The reason for this apparently
contradictory finding is that ammonia needs nitric oxide emissions to
form aerosols, and these latter emissions are expected to decline in the
US, Europe, and eastern China. The authors say that this means that
increased food production shouldn’t affect air quality—if we can control combustion emissions.
Tsigaridis, an associate research scientist at Columbia University
and NASA’s Goddard Institute for Space Studies warns, however, that this
is no excuse to give livestock production and fertilizers a free pass.
Both contribute to climate change, deforestation, and the pollution of
our waterways, he says. “Air quality is only one piece of the puzzle.
