This text is taken from Courrier de la planete. Click here to subscribe.
Why do we no longer hear about “acid rain” when for almost ten years in the past, this was one of the most alarming concerns of environmentalists?, asks Jean Chalifoux.
In the 1980s, acid rain was the number one threat to the environment. This peril, capable of devastating forests in Europe, killing life in lakes in North America and damaging crops as well as human health in China, even constituted one of the main sources of friction between Ottawa and Washington.
Four decades later, these rains rarely make their way to the headlines. For what ? asks Jean Chalifoux. For 40 years, the West has made giant strides in its fight against acid rain, but a new peril threatens life just as much today: fine particles (PM2.5), considered atmospheric enemy number one. one by the World Health Organization (WHO).
It was a study carried out in 1963 by Gene Likens which first sounded the alarm about acid precipitation. By analyzing rain samples collected in the White Mountains of New Hampshire, he noticed that the drops collected were a hundred times more acidic than normal. Alerted by these results, the scientific community is looking into the causes of this acidification and pointing to two culprits: nitrogen oxide (NOx) and sulfur dioxide (SO2), two chemical compounds spewed into the atmosphere after combustion. of fossil fuels.
Eastern Canada and its Canadian Shield are particularly vulnerable to acid rain. In addition to car exhaust gases, rich in NOx and SO2 before the widespread use of catalytic converters, the chimneys of coal factories in the American Midwest and industrial areas of Pennsylvania and New England spew quantities of the chemical compounds responsible for rains.
Canada and its civil society took stock of the threat from the 1980s. The Canadian Coalition Against Acid Rain took shape in 1981: it became the first Canadian pressure group registered in Washington and played a leading role in raising awareness. and reduce acid fumes on both sides of the border.
In 1985, the federal government and seven Canadian provinces signed a declaration that paved the way for the Eastern Canada Acid Rain Program. The latter plans to “limit SO2 emissions to 2.3 million tonnes in eastern Canada no later than 1994.” However, it was also important to bring the Americans into the picture, since half of the acid deposits found on Canadian soil came from the United States.
It was not until 1991, almost 30 years after Gene Likens’ sampling, that Ottawa and Washington ratified the Canada–United States Air Quality Agreement. Former Prime Minister Brian Mulroney first received a dismissal from US President Ronald Reagan, before convincing his successor, George HW Bush, of the importance of purifying the air — and relationships. — between the two countries.
Canada took another turn in 1998 when the 26 federal, provincial and territorial ministers of Energy and the Environment signed the Pan-Canadian Strategy on Acidifying Emissions after the Year 2000. This aimed to protect the most vulnerable environments by further reducing the permitted quantity of SO2 in the Canadian atmosphere.
In 2014, the volume of sulfur dioxide emitted by Canada had decreased by 63% compared to the 3.1 million metric tonnes released in 1990. South of our border, the agreement had, during this same period, helped reduce emissions by 79%, dropping them from 20.9 million metric tons in 1990 to 4.3 million metric tons 24 years later.
The emergence of tar sands in Western Canada, however, has shifted the problem of acid rain to the other side of the country. In 2013, an exhaustive study carried out by Paul Makar, scientist for Environment Canada, estimated that rains now threatened an area the size of Germany north of Alberta and Saskatchewan. Other research subsequently tempered the threat, but the fact remains that the production of a barrel of synthetic crude oil from tar sands emits twice as much nitrogen oxide and sulfur oxides (SO). than its conventional equivalent, according to the Pembina Institute.
If the severity of acid rain has decreased over the decades, even in China, it is now the presence of micro and nanoparticles that concerns public health, explains Professor Parisa Ariya of McGill University. “We have reduced NOx and SO2 emissions, but we have increased those of fine particles (PM2.5). Now, they are the leading cause of deaths linked to air quality. »
A WHO report published last year held PM2.5 pollution responsible for as many deaths as smoking, which kills eight million humans each year.