Phoenix is a wonderful place to live if you enjoy spending time out of doors. However, there is a catch. The conditions that make for our predictable-practically-perfect weather (at least in the winter and spring) has also led to some serious air quality issues.
Every year the Arizona Department of Environmental Quality releases a number of high pollution advisories warning Arizonans that it may be unhealthy to venture out of doors, particularly if you have a medical condition such as asthma. July and August show the highest number of “very unhealthy days”. In fact in July 2013, there were seven “very unhealthy days” reported.
Over the next few posts, I will review some of the unique conditions that make up our Arizona environment and spend some time on the major components that make up the “poor air quality” reported by the Arizona Department of Environmental Quality
To begin, one thing is obvious: Phoenix is a desert. Like most deserts, our climate is characterized by high pressure conditions that camps out over the region for extended periods of time resulting in warm (and hot!), dry, and generally clear conditions. Half of the yearly rainfall occurs during the winter when brief pacific storms move through the region. During the monsoon season, from July to September, moister from the south brings higher humidity and most of the remaining rainfall, often in the form of violent thunderstorms.
During late fall to early summer, high pressure sits over the region like a glass lid, repelling the volatile weather fronts that plaque much of the United States and keeping the interior toasty warm and dry. What little wind does occur is generated by local temperature and elevation variations. This, along with the extremely low humidity during this time of year, allows airborne particles -dust, pollutants, pollen-to drift in the atmosphere for a very long time rather than being cleaned away by rain or ocean breezes.
Conditions change somewhat during the second half of the summer when high pressure travels north a bit allowing monsoon moisture to move into the valley. The increased volatility in the local wind patterns not only produces thunderstorms (and the hope of rain) but also massive dust storms. These giant walls of dust can transport appreciable quantities of organic as well as inorganic material as they move across the valley. Exposure to these clouds of organic bits of plants, mold and who-knows-what-else (think Maricopa feed lots) can trigger severe allergy and asthma attacks. An analysis of material from dust storms in Tempe showed they contain an average of 11% organic material.
Although monsoon storms have the potential to bring rain and some clearing of the air, summer is the time when ozone becomes a problem. That will be the topic of my next post.