Pima Couny's air quality index crossed over into the orange level today after flirting with it much of the morning. 

An orange reading signifies the air is unhealthy for sensitive groups such as asthmatics and others with heart or lung diseases, as well as seniors and the very young. To keep tabs on the AQI, bookmark this site.

Shortly after 11:30 a.m., the county Departrment of Environmental Quality issued an air pollution advisory because of the high readings. The culprit is particulates, uprooted by high winds from their natural homes in farms, mines, dirt roads, vacant lots and disturbed areas.

At 1 p.m. today at a monitor near Grant Road and First Avenue, the AQI registered 101 for large particulates and 89 for fine particles. At 2 p.m., the readings climbed to 103 for large particulates and 91 for the fine particulates. At 3 p.m. and 4 p.m, the readings were at 104 for large particles and 93 for fine particles.

At 101, the air crosses into the realm in which it's considered unhealthy for sensitive groups

Earlier readings today:

-- At 10 a.m., the AQI was at 95 for large particulates, also known as PM10 particles, and 84 for fine particulates, aka 2.5 particles.

-- At 11 a.m., the index had nudged upward to 97 of PM10s and 87 for PM2.5.

-- Noon, it hit 99 for PM10 and 89 for 2.5. 

Particulate matter is made of tiny specks of soot, dust, and aerosols that are suspended in the air.

The earlier readings were at the upper end of the moderate level on the AQI--which is colored yellow. A moderate reading means that people with heart and lung diseases should try to limit their outdoor exertion. 

When and if the air gets worse, the AQI readings turn red, then puple, then burgundy. Those colors represent gradually worsening pollution levels that in all cases are unhealthful for everyone.

On April 9 the air was rated burgundy, or hazardous, at a Green Valley monitoring site due once again to high PM 10 levels. That was the highest PM10 reading on on record in Pima County.

When the air is rated hazardous, which had never happened before here, people are wise to stay indoors. But today, "at this point, we're not saying not to go outside. We're saying that when you are outside you should limit your exertion levels," said Beth Gorman, a DEQ program manager. "If people are supersensitive, they may want to restrict their exposure to outside air."

The winds were high today and yesterday evening, hitting 29 miles per hour at 10 a.m. today and dropping to 27 mph by noon near Houghton Road and I-10 on the far east side.

In separate readings -- the actual concentrations of PM 10s -- the levels peaked late Thursday night and early today. At about midnight, PM10s hit 304 micrograms per cubic meter, and dropped to 232 by 1 a.m. By 1 p.m., the level was 129.

The AQI index is rising even as the concentrations are dropping because the AQI reflects 24 hours worth of pollution readings, Gorman said. Every hour, as the AQI drops a low reading from yesterday, the index rises. It's now a race against time to see if the AQI will hit 101 before the particle levels drop enough to put us out of the danger zone.

If such readings stay above 150 over 24 hours, we've exceeded the EPA particulate standard, but that didn't happen Thursday. It won't be known if it happened today until all hourly totals are averaged -- after midnight.