What smog is and why New York City gets it

Smog in New York City forms when sunlight reacts with pollution from cars, trucks, power plants, and industrial sources. The result is a haze that reduces visibility and contains ground-level ozone — a gas that irritates your lungs. On hot, still days, when air doesn't move much, smog builds up faster and gets worse.

NYC doesn't create all its own smog. Wind patterns carry pollution from power plants and factories in New Jersey, Pennsylvania, and upstate New York into the city. This means even on days when local traffic is light, the air quality can still be poor. Summer months — June through September — are when smog is most common, because heat and sunlight speed up the chemical reactions that create it.

The city monitors air quality continuously and issues alerts when pollution reaches unhealthy levels. These alerts tell you when to limit outdoor activity, especially if you have asthma, heart disease, or are over 65.

Key Takeaways

  • The New York City Department of Environmental Protection measures air quality hourly and posts the current Air Quality Index on its website and the AirNow app.
  • An Air Quality Alert is issued when the forecast predicts unhealthy air, usually on hot summer days when ozone levels rise.
  • People with asthma, heart disease, children under 15, and adults over 65 are most at risk from smog and should limit outdoor exercise on alert days.
  • You can check the forecast for your neighborhood and sign up for text or email alerts through the city's official air quality pages.

How to check New York City's air quality right now

The Air Quality Index (AQI) is a number from 0 to 500 that tells you how clean or polluted the air is. The New York City Department of Environmental Protection updates this number every hour on its website at dec.ny.gov. You can also use the free AirNow app, made by the U.S. Environmental Protection Agency, which shows the AQI for your exact location in the city.

The AQI is color-coded: green means good air, yellow means moderate (acceptable for most people), orange means unhealthy for sensitive groups, red means unhealthy for everyone, and purple means very unhealthy. When the forecast predicts orange or worse, the city issues an Air Quality Alert. Most alerts are issued the day before or the morning of the bad air day.

You don't have to check manually every day. The city offers text and email alerts through its website. You can choose to receive alerts only when air quality reaches a certain level, or for your specific neighborhood if you live in a part of the city that sometimes has better air than others.

What to do when there's an Air Quality Alert

On alert days, people in sensitive groups should reduce time outdoors and avoid strenuous exercise. Sensitive groups include children under 15, adults over 65, people with asthma or other lung disease, and people with heart disease. If you're in one of these groups and must go outside, wear an N95 or P100 mask — a regular surgical mask does not filter ozone.

If you don't have a respiratory condition, you can usually go about your day on an orange alert. On red or purple alerts, the city recommends that everyone limit outdoor activity. Schools may cancel outdoor sports or recess. Some employers ask workers to stay indoors or work from home.

Keep windows closed on alert days if you don't have air conditioning, or use air conditioning to filter incoming air. If you have asthma, keep your rescue inhaler with you. If you notice chest pain, shortness of breath, or wheezing that doesn't improve with your inhaler, call 911.

Who is most affected by smog

Children and older adults are hit hardest by smog because their lungs are still developing or have weakened over time. People with asthma, emphysema, chronic bronchitis, or other chronic lung disease face real risk — ozone inflames the airways and can trigger attacks. People with heart disease are also vulnerable because air pollution stresses the cardiovascular system.

Pregnant people should also take air quality alerts seriously, as some research suggests that exposure to ozone during pregnancy may affect fetal development. If you fall into any of these groups, check the air quality forecast before planning outdoor activities, especially exercise.

People who work outdoors — construction workers, delivery drivers, park maintenance staff — face higher exposure on alert days. If your job requires outdoor work, talk to your employer about whether you can shift tasks indoors or adjust your schedule on high-pollution days.

The difference between smog alerts and other air quality warnings

New York City issues different types of air quality warnings depending on what pollutant is the problem. An Ozone Alert (the most common type of smog alert) is issued when ground-level ozone is forecast to be unhealthy. A Particulate Matter Alert is issued when fine particles in the air — from dust, smoke, or industrial sources — reach unhealthy levels. These often happen after wildfires or on days with poor air circulation.

Both types of alerts use the same color-coded AQI system and the same recommendations: sensitive groups should limit outdoor time. The main difference is what's causing the pollution. Ozone alerts happen on hot, sunny days. Particulate matter alerts can happen any time, especially in fall and winter when air doesn't mix well.

The city also issues Dust Advisories when Saharan dust or other dust from distant sources reaches NYC. These are less common but can significantly reduce air quality. All of these alerts are posted on the same city website and app, so checking one source covers all of them.

Long-term health effects of repeated smog exposure

Living in a city with frequent smog means breathing polluted air many days a year. Over time, this can reduce lung function — your lungs don't work as well as they should. Children who grow up in areas with high ozone exposure may develop asthma or have smaller lung capacity as adults, even if they don't have asthma now.

Older adults and people with existing heart or lung disease face the biggest long-term risk. Repeated exposure to ozone can worsen asthma, trigger heart attacks, and increase the risk of early death in people with heart disease. This is why people in these groups should take air quality alerts seriously, not just on individual bad days but as part of a pattern of protecting their health.

If you live in an area of the city that frequently has poor air quality, talk to your doctor about whether you should take extra precautions or whether your medications need adjustment. Some people benefit from using an air purifier indoors, though these work best in a single room with the door closed.

How the city measures and forecasts air quality

The New York City Department of Environmental Protection runs a network of air quality monitoring stations across the five boroughs. These stations measure ozone, nitrogen dioxide, sulfur dioxide, particulate matter, and other pollutants every hour. The data feeds into the Air Quality Index, which is updated hourly on the city's website.

To forecast tomorrow's air quality, the city uses weather models and historical pollution patterns. If the forecast shows high temperatures, stagnant air, and strong sunlight — the conditions that create ozone — an alert is issued. The forecast is usually issued by 4 p.m. the day before, though sometimes alerts are issued the morning of if conditions change overnight.

The city also works with the EPA and neighboring states to track pollution that blows in from outside the city. This regional coordination helps explain why NYC sometimes has poor air quality even when local sources aren't the main problem.

Frequently Asked Questions

Can I exercise outdoors on an orange air quality alert?

If you're in a sensitive group — children, older adults, or people with asthma or heart disease — you should avoid strenuous outdoor exercise. If you're not in a sensitive group, moderate outdoor activity is usually safe, though some people choose to exercise indoors anyway. Check the specific alert details on the city website, as recommendations sometimes vary.

What kind of mask protects against smog?

An N95 or P100 respirator mask filters ozone and particulate matter. Surgical masks and cloth masks do not. N95 masks are inexpensive and widely available. Make sure it fits snugly around your nose and mouth — a loose mask won't protect you. If you have a beard or facial hair, the seal won't work well.

Does air conditioning help with smog?

Yes. Air conditioning filters incoming air and keeps polluted outdoor air out of your home. Keep windows and doors closed on alert days. If you don't have air conditioning, closing windows and staying indoors is still better than being outside, though the air inside will gradually become less fresh.

Why does smog happen more in summer?

Heat and sunlight speed up the chemical reactions that create ground-level ozone. Summer also brings stagnant air patterns where pollution builds up instead of blowing away. Winter air is usually cleaner because cooler temperatures slow ozone formation and wind patterns change.

Where can I sign up for air quality alerts?

Visit the New York City Department of Environmental Protection website at dec.ny.gov to sign up for text or email alerts. You can also read the free AirNow app, which sends notifications when air quality reaches unhealthy levels in your location.