I returned to Houston six months ago after being in Omaha, NE for nearly five years during which time I had almost forgotten what an Air Quality Alert was. It didn't take long after my return to see the first one issued in late March. I honestly do not remember seeing alerts for bad air quality that early in the year when I was younger, but I suppose it did occur occasionally. However, it is undoubtedly getting worse as Houston's population continues to grow and expand.
A quick aside: The population in Houston's MSA (Houston, Sugarland, & Baytown) in 1970 was 2,201,849. That grew, on average, 3.55% per year to 3,767,218 in 1990. Today the population sits at an estimated 6,086,538 representing an average growth rate of 2.9% since 1990. We'll come back to these stats in a bit.
To understand why the public has to contend with poor air quality is not a mystery. In fact, all I have to do is look along the horizon on a clear, wind-less, morning and I can see the culprit very clearly as I crawl to work in rush hour traffic. It's that nasty brown layer that seems to hug the horizon in every direction. That visible layer is also known as smog. The early morning Houston smog is a result of the chemical "leftovers" that every combustion engine releases into the atmosphere. Our cars, planes, buses, construction equipment, refineries, and anything else that involves burning a combustible fuel all contribute to smog, albeit some more than others. However, it is a necessary evil. We all have to work and many of us have to commute to our jobs each day. Refineries have to refine the fuel we use in our vehicles. Airplanes have to carry vacationers along with business women and men while using the refined fuel to fly them around. And so on, and so on.
Today, in Houston's metro area, including Sugarland and Baytown, there are about 6,100,000 people. Let's assume approximately 45% commute to and from work each day (at least 20 round trip miles). That's a whopping 2,745,000 vehicles traversing Houston metro streets twice a day. That does not include air traffic, boat traffic, freight truck traffic, and others. It's probably a pretty safe estimate too considering 91% of Houston households have at least 1 car (35% have 2 or more). The average household is 2.83 people. That equates to about 2,155,000 households in the metro. 15% are retired people. Therefore, 1,831,750 are working class that have 1,282,225 cars (35% times number of working class households times 2 cars), and then 1,190,637 for the remaining 65% of working class households with one car. Take into account unemployment of 8%... CONSERVATIVELY, 2,275,033 vehicles of working class citizens with jobs are driven each day. Not including commuters from other cities not part of the metro population. No matter how you slice it, there are multiple millions of vehicles traveling Houston's streets every single day. Along with the 2,300 or so commercial flights every day (airline stats). And it's only getting more congested.
The following table reveals how much annual pollution is emitted by a passenger car (estimates as of year 2000).
Using 2,275,000 vehicles from the calculation above, which we know is conservative, and the table above, here are some figures to consider.
Per Year, Houston traffic contributes at LEAST:
87,701 Tons of Hydrocarbons
654,062 Tons of Carbon Monoxide
43,452 Tons of Oxides of Nitrogen
13,024,375 Tons of Carbon Dioxide
TOTAL ---> 13,809,590 Tons of Pollutants
AND 1,321,775,000 Gallons of Gasoline
(multiply # of Gallons above by avg. gas price of $3.75 ) -- Wowza!
13,809,590 TONS of Pollutant each year, conservatively, solely by the vehicular traffic in the Houston Metro. That's equivalent to 24 of the largest oil tankers in use today filled to the max with pollutants and delivered to the city each year. No wonder why the pollution is visible daily. 37,834 tons get released into the atmosphere each day!!
Now that we have some very rough idea of the amount of pollution generated solely by vehicular traffic, and we know it is millions of tons worth a year. What actually causes the air quality alerts? After all, it's not everyday we have bad air quality even though about the same amount of pollution fills the atmosphere daily.
When the sun's ultraviolet rays come into contact with the molecules of the various pollutants that are suspended in the lower atmosphere it causes them to react with each other to form new, more harmful, molecules. Specifically, when the reaction forms the gas Ozone which is 3 oxygen atoms combined - that is bad news. Right now, and every time you take a breath, the oxygen atoms you breathe are made up of a diatomic oxygen molecule meaning it is composed of 2 atoms of oxygen (O2). You'd think adding a third atom would be better in a sense. It's more oxygen right? Yes. Unfortunately, it's not a healthy form of oxygen. Ozone, O3, without going into too much detail here, causes inflammation of the walls of the lungs exacerbating symptoms of those with existing lung disorders such as asthma, emphysema, bronchitis, and other lung problems. If the ozone concentration is extreme enough even healthy people will begin coughing and experiencing difficulty breathing if outdoors for some length of time beyond 30 minutes or so. The most frail, babies and the elderly, can actually experience severe enough problems to cause hospitalization most extreme circumstances. Read all about the health effects in more detail here.
Other environmental factors that exacerbate the levels of Ozone are temperature, wind speed, wind direction, and a strong inversion in the lower atmosphere. When the temperature increases during the daytime it acts to increase chemical reactions. So temperatures into the 90's or 100's can send the level of ozone into the extreme range in no time. That is mainly why the worst air quality days occur in the summer months. Wind is important because it can act to disperse the concentration of pollution through mixing in the lower atmosphere and carry it away from populated areas. Strong winds lead to decreased Ozone. Light winds or no wind is a recipe for bad air quality. Wind direction plays a role as well by transporting pollution from industrial areas into the city or rural areas. The largest refineries are east of the city, so a very light breeze from the east can send pollution and the resulting ozone into the extreme category over the city or rural areas in a short period of time. Lastly, an inversion acts to trap air in the lower portion of the atmosphere and prevents mixing which would help dissipate the pollution quicker. If the pollution gets trapped overnight and more pollutions accumulates the next day, when temperatures rise Ozone concentration will too and possibly become extreme by peak heating time in the afternoon.
Because of the potential for adverse health effects as a result of ozone formation, the Texas Commission on Environmental Quality (TCEQ) monitors the ozone levels in Texas and in the Houston Metro. The National Weather Service through the TCEQ issues air quality alerts.
Unfortunately, this is the way of life in a city as large as Houston. And Houston is one of many cities in the nation with Ozone pollution. According to WebMD, Houston is No. 8 on the list of cities with unhealthy air quality. That's up from No. 4 though; some good news there. http://www.webmd.com/asthma/ss/slideshow-worst-sm og-cities
As summer approaches temperatures will rise and the wind will subside. That's when Houston can expect many more Air Quality Alert days. It's best to keep the little ones and old/wise ones indoors during the hottest and sunniest part of the day and limit overall outdoor exposure on days when the air quality is going to be dangerous.
Today's Current Ozone Level (Courtesy TCEQ)
Check back often as I will be updating on expected severe weather and tropical weather as it occurs. On uneventful weather days I'll be composing random weather related blogs for your entertainment.
Thanks for reading!