APCD dunes study is flawed
November 14, 2011
OPINION By ED WAAGE
The Air Pollution Control District has responded to comments concerning the proposed regulation of the Oceano Dunes vehicle riding area which will be considered at the APCD Board meeting this Wednesday. The regulation is based upon an APCD study which found that vehicle activity on the dunes was responsible for additional particulate matter, or PM10, generated as a result of that activity.
One of the criticisms I had of the APCD’s study was the method they used to establish that on days when there was increased vehicle activity, there was an increase in PM10.
The method involved a comparison between a vehicle riding area and a non riding area. The non riding area was used as a control to account for any other factors other than vehicle activity on the results. Fifty highest vehicle activity days were then compared with fifty lowest vehicle activity days.
The study found there was 25 percent more PM10 on the highest use days yet the control did not experience such an increase which gave credence to the results.
However, I pointed out that APCD’s method was flawed since they used almost two months of data for the riding area before the non riding area (control site) monitoring equipment was even in operation. In addition, the study was supposed to be one year long starting April 2008, yet the study included the month of March 2008 without stating so in the study.
The APCD’s response to my criticism was jaw dropping. Instead of admitting that the criticism was valid and that the finding was in error, the staff report states that they did not in fact, need a control site at all and stood by their original finding of increased PM10 with increased vehicle activity.
The problem is this: there are far more visitors to the park during summer months than winter months which means the high vehicle use days will generally occur in the summer months and low use days in the winter months. This would likely inject a strong seasonal bias in the results when comparing high use days with low use days.
A close examination shows this is the case: it was warmer and drier during the high 50 use days which favors more PM10 while it was cooler and wetter during the 50 lowest which favors less PM10. There were eight days when it rained during the 50 lowest use days while there were only a couple of days with trace amounts of rain for the high use days.
The inclusion of that additional month of March 2008 also had a significant effect. Easter occurred on March 23rd which led to more vehicle activity during that period. March is also a windy month which generates more PM10. The net effect is to boost the correlation of PM10 with vehicle activity.
Seasonal variations of PM10 are well known with spring and summer months generally having higher PM10 while winter months the lowest. Instead of finding that vehicle activity causes more PM10, the APCD simple affirmed that there are these seasonal variations.
We need to get the science right if we are going to impose regulations based upon that science. Right now, I do not believe we have the science right.
Ed Waage is a Councilmember of the city of Pismo Beach and represents the city on the APCD Board.