Tilapia

Sometimes work-related tasks make for entertaining speculation. Today a co-worker asked:

Does anyone know why the 24-hour SO2 levels at Calexico were so high in August of 2006 (max of 0.041 ppm when all other years had a max of no higher than 0.003 ppm)?

Sulfur dioxide isn't much of an air pollution problem in California, except maybe around oil-industry locations in Ventura County, and not even much there. The Imperial Valley and areas along the border aren't oil country, so it's a valid question why there would be a problem. I replied:

The top four days with high SO2 in Calexico in 2006 were all in August, suggesting something episodic. There are power plants in the area, including geothermal power (H2S), and fossil fueled (natural gas) powered plants, plus other industry. I don’t know the cause – maybe they were using higher-sulfur fuels for a brief period?

Another co-wroker replied:

It is unlikely that gas fired plants were the problem, and there are no high sulfur fuels that are allowed there. The geothermal plants are a possibility, but my impression is that they are located quite a ways from Calexico.

So, what caused the high SO2? What else was going on in the Imperial Valley in August 2006?

I don't know if this is the cause, but this article from July, 2007 certainly suggests a possibility:

SALTON CITY (CBS 5 / AP) ― Millions of tilapia died in the annual summertime Salton Sea fish kill in what is described as the largest die-off ever at the giant desert lake.

Salton Sea Authority Project Manager Dan Cain says it's too early to estimate how many tilapia died, but the number appears to have surpassed the three million that died in August 2006.

Fish die-offs occur at the lake every summer because of natural biological and chemical reactions that sap oxygen from the water during July heat waves when temperatures soar near 120 degrees.

There are an estimated 200 million tilapia in the Salton Sea.

...The Salton Sea authority has about 45-thousand dollars in its budget to remove the fish.

Cain says, "Everywhere you looked, there were dead fish. Fish were floating as far as the eye could see."

Like I say, who knows if this is what my co-worker was looking for, but certainly millions of dead fish would create an air contamination issue for someone.