Discussion: particulate levels

were better at 11a than 6? It wasn't noticeable while I was at the track - no burning, no haze etc. But the sunrise seemed a bit more diffuse and reddish in tone.

I don't know how good airgov's mapping really is. but it was over 100 at 7am, then gradually dropped to about 50 and leveled off there. this is fine particulate, 2.5 microns or smaller, don't know how that effects visibility.

so apparently the AQ maps can't be too literally interpreted, this explanation from the Missouri Dept. of Resources:

"One issue to point out when looking at the AirNow current conditions maps is that EPA’s AirNow system uses a ‘surrogate’ algorithm to approximate the PM2.5 AQI based on data trends monitored in the recent past. Many state agencies utilize semi-continuous PM2.5 monitoring methods that report hourly concentrations. EPA does not have a 1-hour NAAQS established for ambient PM2.5 concentrations. The regulatory AQI for PM2.5 (and subsequent comparison to the 24-hour PM2.5 NAAQS) can’t be calculated until a full 24-hour period (midnight-to-midnight) has elapsed. This is why some of the area shading on the AirNow current conditions map appear to be ‘monitor specific’ . The surrogate algorithm is using short term concentrations to estimate what the AQI ‘could be’ at the end of a 24-hour period if recent trends continue. Short term peaks may occur at discrete monitors from time-to-time due to spatial and temporal short term air concentration variability between monitoring sites. The reason EPA uses a surrogate is explained best on the last two slides of this link. http://www3.epa.gov/airnow/ani/pm25_aqi_reporting_...

The archived maps on the AirNow.gov website use the preliminary 24-hour concentrations to report the previous day’s AQI (midnight-to-midnight). http://www.airnow.gov/index.cfm?action=airnow.maps... These maps generally show area wide impact where applicable. The AQI pollutant specific ‘Loop Maps’ will typically show the surrogate calculation based on the data available at that hour during the 24-hour period."

It sounds like you can't use that information to find out 'what is the air quality now'.?.?

I get the impression for a rule of thumb (also from my own observation) that if it looks bad, its really slightly better than it looks. Got an e-mail in to see what he says.

this seems to indicate that one can take the current maps at face value...guess I wasn't really understanding the above. We need some PHD candidate analysis.

"Use the current conditions maps as an indicator of what the current level and recent air quality trends have been to make a choice about making the morning run or not (i.e. one has the choice to reduce their exposure to current air pollution conditions regardless of whether several hours later the 24-hour average meets or exceeds the level of the standard)."