An air quality alert means that the air itself in the city can be dangerous, especially for the very young and people with heart and lung problems.
Beautiful sunsets depend on haze in the air, but the hazy atmosphere means the air is full of small particles, mainly from industrial pollution. The other main bad air culprit is ozone gas, made when the exhaust of a vehicle on the street is acted on by sunlight. The ozone and the particles combine to narrow the lung's air passages. The result is a person becoming easily exhausted.
"There's a subjective feeling of walking through glue, but climbing stairs feels worse for someone who has lung or heart disease," said Dr. Edward Eden of St Luke's Roosevelt Hospital.
Heart disease patients are in trouble because the heart must beat faster to circulate blood to the skin for cooling. The strain can lead to irregular heartbeats, and even strokes and heart attacks.
Others at risk are smokers, people who are overweight, and those with high blood pressure or high cholesterol.
The air quality may get worse. High humidity later this week won't make pollution worse, but it will make you feel more uncomfortable. Humidity makes it harder for sweat to evaporate, which means you won't cool off very well.
To avoid the poor outside air quality, find an air-conditioned space, such as a mall or a movie theatre. Even the A.C. at work may be better this week than being at the beach. It's not a good idea to exercise in this weather for people with heart or lung disease. Make sure to stay hydrated, so you can sweat, which will cool you off.