The U.S. has come a long way in cleaning up its air. The Clean Air Act of 1970 made air pollution catastrophes like the 1948 smog that killed nearly 40 people near Pittsburgh a distant memory. But while the air is much cleaner overall, smoke from wildfires is threatening the progress that’s been made, as particulate pollution from wildfires has been growing across the Northwest U.S. over the past 30 years.
Tiny wildfire smoke particles, which can sometimes go unnoticed in small concentrations, are known as PM2.5 — referring to particulate matter that is less than 2.5 micrometers in diameter. These particles are about four times smaller than dust, pollen, or mold particles, and about 30 times smaller than the diameter of a human hair. They can reach deep into the lungs and the bloodstream, raising the risk of heart disease, lung disease, and diabetes.
A smoke wave occurs when the concentration of PM2.5 is at least 20 micrograms per cubic meter for two or more consecutive days. For perspective, this level of PM2.5 falls within the moderate range of the EPA Air Quality Index, so it is not uncommon, and one study found that 46 million people in the Western U.S. were exposed to at least one smoke wave between 2004-09. While these levels are substantially lower than those recorded in China and India during their worst air quality stretches, seemingly low concentrations of PM2.5 can substantially raise health risks. Small doses of this smoke pollution affect the chemistry inside the body, slowing blood flow and oxygen to the heart, developing plaque on the inner walls of arteries, and interfering with liver functions.
As temperatures climb in a changing climate and fire risk increases as a consequence, more people will be exposed to wildfire smoke in the coming decades. Under a moderate greenhouse gas emissions scenario, which is close to our current path of emissions, the total area burned by wildfires is projected to increase between 60 to 120 percent by mid-century compared the end of the 20th century. Even with the best air pollution standards, the climate change induced risk to long-term human health from wildfires may continue to grow.
Methodology: A smoke wave is defined by Liu et al (2017) as two consecutive days with PM2.5 concentration at least 20 micrograms per cubic meter. This PM2.5 concentration corresponds to an EPA Air Quality Index of 67, which lies within the bounds of the moderate designation (13 to 35 micrograms per cubic meter).
Marekani imefanya maendeleo makubwa katika kusafisha hewa. Sheria ya hewa safi ya 1970 ilifanya majanga ya uchafuzi wa hewa kama vile smog ya 1948 ambayo iliua watu karibu 40 karibu na Pittsburgh kumbukumbu ya mbali. Lakini wakati hewa ni safi zaidi kwa ujumla, moshi kutoka kwa moto wa misitu unahatarisha maendeleo yaliyopatikana, kwani uchafuzi wa chembe kutoka kwa moto wa misitu umekuwa ukiongezeka katika Kaskazini Magharibi mwa Marekani katika miaka 30 iliyopita. "Kipande kidogo cha moshi wa moto wa mwituni, ambacho wakati mwingine kinaweza kutambuliwa kwa kiasi kidogo, kinajulikana kama ""PM2.5,"" ikirejelea chembe ndogo ambazo zina kipenyo cha chini ya 2.5 micrometers." Chembe hizo ni ndogo mara nne kuliko vumbi, chavua, au kuvu, na mara 30 ndogo kuliko kipenyo cha nywele za binadamu. Zinaweza kuingia ndani ya mapafu na mtiririko wa damu, na hivyo kuongeza hatari ya kupatwa na magonjwa ya moyo, mapafu, na kisukari. Mlipuko wa moshi hutokea wakati mkusanyiko wa PM2.5 ni angalau 20 micrograms kwa mita ya kiunzi kwa siku mbili au zaidi mfululizo. Kiwango cha PM2.5 katika hewa ni sawa na kiwango cha wastani cha EPA, na utafiti unaonyesha kuwa watu milioni 46 katika nchi za Magharibi ya Marekani waliathiriwa na moshi wa moshi kati ya mwaka 2004 na 2009. Ingawa viwango hivi ni chini sana kuliko zile zilizorekodiwa nchini China na India wakati wa vipindi vya ubora wa hewa mbaya zaidi, viwango vya chini vya PM2.5 vinaweza kuongeza hatari za afya. Mazao madogo ya moshi huu huathiri kemikali ndani ya mwili, kupunguza mtiririko wa damu na oksijeni kwa moyo, kuunda plaque kwenye kuta za ndani za mishipa, na kuingilia kazi za ini. "Kwa sababu ya kuongezeka kwa joto katika hali ya hewa inayobadilika na hatari ya moto ikiongezeka kama matokeo, watu wengi watakabiliwa na moshi wa moto wa mwituni katika miongo ijayo. """ Katika hali ya uzalishaji wa gesi ya chafu ya wastani, ambayo ni karibu na njia yetu ya sasa ya uzalishaji, eneo la jumla la moto wa misitu linatarajiwa kuongezeka kati ya 60 hadi 120% kufikia katikati ya karne ikilinganishwa na mwisho wa karne ya 20. Hata na viwango bora vya uchafuzi wa hewa, hatari ya mabadiliko ya hali ya hewa kwa afya ya binadamu ya muda mrefu kutoka kwa moto wa misitu inaweza kuendelea kukua. "Mfano: ""Wimbi la moshi"" ni siku mbili mfululizo na PM2.5 mkusanyiko wa angalau 20 micrograms kwa mita ya kiunzi." Kiwango cha PM2.5 kinalingana na kiwango cha EPA cha ubora wa hewa cha 67 na iko ndani ya mipaka ya kiwango cha wastani (mikrogram 13 hadi 35 kwa mita ya kiunzi).