Large and intense wildfires in the Pacific Northwest (PNW) of the USA are having an impact on the seasonal pattern of air pollution, causing a spike in unhealthy pollutants, new research has found. The smoke is “undermining clean air gains” according to Science Daily, “posing potential risks to the health of millions of people.”
The research, led by scientists at the National Center for Atmospheric Research (NCAR), found that levels of carbon monoxide (CO) have increased sharply as wildfires spread in August. It was published in Nature Communications.
“Wildfire emissions have increased so substantially that they’re changing the annual pattern of air quality across North America,” said NCAR scientist and lead author, Rebecca Buchholz. “It’s quite clear that there is a new peak of air pollution in August that didn’t used to exist.”
The presence of CO usually suggests the presence of other air pollutants. Levels are usually lower in the summer thanks to chemical reactions from changes in sunlight. The findings, therefore, indicate “the extent of the smoke’s impact.” The gas is less of a health concern outdoors but it does indicate the presence of other, more harmful pollutants including aerosols and ground-level ozone that can form on hot summer days.
The research team used satellite observations of atmospheric chemistry and global inventories of fires to track wildfire emissions over the past two decades. They also employed computer modelling to analyse the potential impact of the smoke, focusing on the PNW, the Central USA, and the Northeast of the country.
Buchholz said that the results were especially striking as CO levels have been otherwise decreasing globally thanks to the advancements made in fighting pollution.
Wildfires have increased in many regions of North America, particularly the PNW. This is for a range of reasons including climate change, increased development, and land-use policies. The fires are becoming factors in air pollution in the region, especially with the reduction in emissions by human activities.
Buchholz and her team used data from two instruments on the NASA Terra satellite. Measurements of Pollution in the Troposphere (MOPITT) has tracked CO continuously since 2002 and Moderate Resolution Imaging Spectrometer (MODIS) both detects fires and provides information on aerosols.
The scientists honed in on the period from 2002, the start of consistent and long-term records of MOPITT data, up until 2018, the final year where complete observations are available when the study began.
The results revealed increased CO levels across North America in August, coinciding with the “peak burning season” of the PNW. The trend was especially pronounced after 2012 when the fire season became more active. Data from the MODIS revealed that aerosols also saw an upwards trend in August.
The scientists had to eliminate other potential emissions sources to be sure that the fires were the cause of the higher pollution levels. CO levels upwind of the PNW were lower in August. This shows that it is not blowing in from Asia. But they also found that the fire seasons in the central US, as well as the Northeast, did not coincide with the increased pollution, meaning that local fires in those regions were not to blame. And studying fossil fuel emissions showed that CO from human activities did not increase in any region from 2012 to 2018.
“Multiple lines of evidence point to the worsening wildfires in the Pacific Northwest as the cause of degraded air quality,” Buchholz said. “It’s particularly unfortunate that these fires are undermining the gains that society has made in reducing pollution overall.”
The results have implications for human health. Wildfire smoke is linked to significant respiratory problems and could affect the cardiovascular system and worsen pregnancy outcomes.
The authors used a computer model, the Community Atmosphere Model to simulate the movement of the PNW fires and their impact on CO, ozone, and fine particulate matter. They found that the pollutants threaten over 130 million people, including 34 million in the PNW, 23 million in the Central US, and 72 million in the Northeast.
The authors also looked at respiratory death rates in Colorado from August 2002 until 2011, compared with the same month from 2012 to 2018. The state was chosen because of its location in the central US region as respiratory death rates there were readily available. They found that the rates increased significantly in the 2012 to 2018 period when fires in the PNW, though not in Colorado, produced more emissions.
“It’s clear that more research is needed into the health implications of all this smoke,” Buchholz said. “We may already be seeing the consequences of these fires on the health of residents who live hundreds or even thousands of miles downwind.”