Meteograms display the forecast and measured data in a timeseries. This is useful for identifying trends or vog episodes, when pollutant levels spike at observation sites. The length of the meteograms is confined to each forecast period of 59 hours. If no plot is shown then observation data are not coming in to compare to model forecasts. The background coloring corresponds to the pollutant threshold levels seen in the model forecasts.
It is important to note that, although sulfate aerosol is a forecast product, sulfate aerosol is itself not measured alone. Sulfate aerosol is measured with other smaller particles that are smaller than 2.5 micrometers (PM2.5), such as dust, sea salt, vehicle exhaust, or pollen. It is for this reason that stations not on the big island often show high measured values of PM2.5 while no vog is forecast for that area.
For a history of the VMAP model parameters click here.