South County Air Quality

The APCD has been investigating the source of the high particulate matter concentrations on the Nipomo Mesa for the past decade.  Several studies performed by the APCD in the Nipomo Mesa area have shown the source of the elevated particulate matter (PM) pollution to be windblown dust from the open sand areas of the Oceano Dunes State Vehicular Recreation Area (SVRA).  The studies provided a comprehensive picture of the characteristics of a typical dust event.

To keep the public informed of periods of deteriorating air quality, the APCD provides a daily air quality forecast for SLO County. SLO County is partitioned into nine air quality forecast zones, and an air quality forecast for a six-day period is provided for each zone.  In the Nipomo Mesa area, there are four forecast zones as shown in the map below, and are named CDF, MESA2, NRP and SLO.

Click the map below to be linked to an interactive version on Google Maps

The darker colors (purple/pink) in the map** signify the location of the greatest dust impacts during a typical blowing dust event.  The public can experience adverse health impacts in areas with blowing dust. 

The blue color represents the SLO forecast area, which in most cases is not impacted by the dust plume.

Children and individuals with compromised cardiac and respiratory systems or related health problems are called sensitive receptors.  Sensitive receptors can experience greater health impacts than the general population during blowing dust events.  Sensitive receptor locations include schools, residential dwellings, parks, day care centers, nursing homes, and hospitals. 

The blowing dust events are typically most frequent in the spring; however, dust events can occur at any time of the year.  The greatest impacts occur when the strong winds blow from the northwest which directs the dust plume inland over the Nipomo Mesa (as shown in the map above) where it can impact residents.  A typical event tends to start around noon and end by the early evening, with peak impacts between 1 pm to 5 pm.  The strongest events can result in blowing dust from 9 am to 7 pm, with peak impacts between noon and 6 pm.  Being aware of typical dust plume characteristics, residents can plan to avoid peak dust impacts.  Particulate concentrations typically return to background levels from the late evening to the morning, so these times are best (health wise) for outdoor activities and exercise.

On November 16, 2011, the APCD Board approved the Coastal Dunes Dust Control Rule 1001 to require implementation of dust control measures on coastal dunes where vehicle activity occurs, to mitigate the impacts of the blowing dust.  Mitigation efforts are currently underway.

** Please note the following in regards to the map above:

• It is important to note that each wind-blown dust event has different characteristics, so the forecast zones on these maps are based on the estimated average magnitude of the particulate matter concentrations observed in each area.
• Borders of each zone are approximate and not meant to be rigid boundaries. PM levels on either side of the boundary line are likely to be very similar. 
• The public should use the air quality forecasts as a guide to help plan their outdoor activities and protect their health during blowing dust episodes.