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Smoke from wildfires in Canada has drifted into the U.S., prompting air quality alerts for Americans as it continues to spread.
But when officials and forecasters classify a city’s air as “unhealthy” or “hazardous,” what does that really mean? The classifications are based on a federal measurement system called the Air Quality Index.
The Air Quality Index is used nationwide to measure the severity of air pollution and categorize the health risks that are involved with various levels of pollution. The index uses six color-coded categories: good (green), moderate (yellow), unhealthy for sensitive groups (orange), unhealthy (red), very unhealthy (purple) and hazardous (maroon).
AirNow.gov
The health impacts included in the index are those that people are likely to experience within “a few hours or days” after being exposed to the air, the National Weather Service Says.
The National Weather Service says that the Environmental Protection Agency calculates the Air Quality Index — a value between 0 and 500 — based on five “major pollutants.”
Those pollutants — ground-level ozone, particulate matter, carbon monoxide, sulfur dioxide and nitrogen dioxide — are all regulated by the Clean Air Act. Of those, ground-level ozone and airborne particles are considered “the greatest threat to human health.”
Each Air Quality Index category, also known as the level of concern, is attached to a certain range of values:
Essentially, the lower the number, the cleaner the air. The only category where air quality is considered “satisfactory” is the one where the index value is no more than 50, although values between 51 and 100 are still considered “acceptable.” After that, the air could pose a risk to at least some people, and that risk only becomes greater as the index value rises.
Once the air is deemed “very unhealthy,” the general public is at risk of experiencing health impacts, which range from a headache and fatigue to much more serious issues such as heart attack or stroke. At “hazardous” levels, the region is experiencing an air quality emergency. Those with chronic respiratory or cardiovascular conditions are more at risk of developing serious health issues as pollution worsens.
Air Quality Index values change constantly throughout the day as weather conditions and weather patterns move through the area. The map below automatically updates to show air quality conditions nationwide.
The EPA’s AirNow.gov site uses the index to provide the latest status for your area. To use the site, enter your ZIP code and a meter will pop up showing you what the value and color category is for your city, as well as the last time that measurement was updated.
AirNow.gov
It also tells you what pollutant is causing issues, who is most at risk for health complications and what activities may be safe to do.
In Minneapolis, for example, the reading on Tuesday morning, June 3, said the AQI for PM2.5, a kind of particulate matter, is 203, meaning “very unhealthy,” and that people who have heart or lung disease, those who are elderly, and children and teens should avoid outdoor physical activity. In these conditions, everyone else should avoid “strenuous” and long outdoor activities.
Smoke spreading from wildfires in Canada was affecting air quality in multiple states on Tuesday.
Parts of Minnesota, Iowa and Wisconsin were most at risk for unhealthy air, according to a federal measurement system called the Air Quality Index.
The index has six ratings: good, moderate, unhealthy for sensitives groups, unhealthy, very unhealthy and hazardous. Sensitive groups include those who have a heart or lung disease, as well as older adults, children and pregnant women.
The map below shows the current air quality across the U.S.
Other states, including Illinois, Michigan, Ohio, Pennsylvania and West Virginia, may see smoke from the fires, although the thickness will vary.
In the Philadelphia region, for example, while smoke is expected to be visible, no major impacts on air quality are expected, CBS Philadelphia reported.
Here’s a look at where the smoke is expected to move on Tuesday and Wednesday.
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Around 200 active fires are burning in Canada, according to the Canadian Interagency Forest Fire Centre. More than 25,000 residents across three provinces had been evacuated due to the blazes as of Sunday, The Associated Press reported.
Electric vehicles (EVs) are rapidly becoming a cornerstone of sustainable urban life, improving air quality and lowering transportation-related emissions. More than a cleaner alternative to internal combustion (ICE) vehicles, EVs are reshaping how cities reduce pollution, improve public health and adapt to climate change. In 2023 alone, global EV sales grew by 35 percent, with U.S. sales rising by more than 40 percent, signaling a dramatic acceleration in adoption. This silent revolution is backed by policy mandates, cost incentives and growing public demand for cleaner transportation options.
EVs significantly reduce air pollutants like nitrogen dioxide (NO₂) and particulate matter in cities. Studies have shown that regions with high EV penetration see measurable improvements in local air quality, contributing to improved public health outcomes. For residents in high-traffic neighborhoods, this shift means fewer tailpipe emissions on their block, cleaner air to breathe and fewer respiratory issues tied to pollution.
Among the biggest advantages of electric vehicles is how efficiently they use energy. Gas-powered cars waste most of their fuel as heat—only about 12 percent to 30 percent actually moves the car. In contrast, EVs use over 75 percent of their energy to power the wheels. That means less waste and more mileage from the same amount of energy. Even when electricity comes from fossil fuels, EVs are still cleaner overall. On average, they deliver the emissions equivalent of 70 to 180 miles per gallon—far beyond what any gas car can match.
There are valid concerns about the carbon cost of battery manufacturing. Producing a typical EV battery emits between 2,400 and 16,000 kg of CO₂. This broad range can be attributed to numerous factors such as battery size, manufacturing location, energy sources used in production and the efficiency of supply chain and material extraction processes. On the flip side, the average gas-powered car emits roughly 43,500 kg of CO₂ over a standard 150,000-mile lifespan, a massive multiplier. Even in the worst-case scenario—battery production combined with coal-generated electricity—EVs still generate less lifetime carbon than ICE vehicles. In regions using cleaner energy mixes like solar or hydro, EV emissions can drop to less than half that of their gasoline counterparts.
Ownership costs also favor EVs. A 2024 Atlas Public Policy study found that EVs can save owners between $7,000 and $11,000 across the lifetime of the vehicle due to reduced fuel and maintenance costs. With fewer moving parts and regenerative braking systems, EVs have lower service requirements compared to ICE vehicles. While insurance premiums can be higher, the total cost of ownership is increasingly favorable, especially as battery prices fall and competition among automakers increases.
Range anxiety remains a barrier to adoption, but charging infrastructure is expanding rapidly. Public and private investment is increasing the number of fast-charging stations across the U.S., as more than 200,000 public charging ports are now available across the country, according to the Joint Office of Energy and Transportation. In cities, the growth of on-street and garage charging stations is making EV ownership more practical for apartment dwellers and those without private driveways. Still, rural communities face slower rollout, and their EV adoption lags behind urban areas by 40 percent in the U.S. as a result. However, these areas often have the advantage of higher homeownership rates and detached housing, making it easier to install home chargers.
Policy also plays a critical role in accelerating adoption. Governments worldwide are introducing mandates to phase out gas cars, alongside incentives like tax credits, rebates and infrastructure grants. The EU plans to phase out new ICE vehicle sales by 2035, and China’s New Energy Vehicle policy aims to have EVs comprise 40 percent of all car sales by 2030, setting the pace for global EV adoption. In the U.S., the Inflation Reduction Act provides up to $7,500 in federal tax credits for eligible EVs, while states and cities add further benefits. At the city level, these policies can directly translate into cleaner bus routes, low-emission zones and incentives for residents to make the switch—shaping healthier, quieter neighborhoods in the process. Major hubs like New York and Los Angeles are electrifying bus fleets, enforcing low-emission zones and providing grants to small businesses that switch to electric delivery vans.
While battery supply chains, recycling and infrastructure equity remain ongoing challenges, the cumulative data support EVs as a cornerstone of sustainable urban transportation. The shift toward electric mobility is not only reshaping the automotive industry—it is redefining how cities combat pollution, adapt to climate change and build long-term resilience.