1. High Wind Blowing Dust April 29, 2011 Exceptional Event
Monitored Exceedances in Southern New Mexico
NMED recorded 74 exceedances of the 24-hour PM10 NAAQS on 23 days in the first half of 2011 (1st & 2nd Quarter QA’d data). Under the DAC and Luna NEAPs ( ) NMED used 18 m/s as the threshold wind speed that causes blowing dust regardless of control measures. NMED feels that this wind speed, by itself, is sufficient evidence that high winds exist and caused blowing dust. For exceedances recorded at monitoring sites not reaching 18 m/s the department provided time series plots of PM10 concentration, wind speed, and wind max; satellite imagery; and news reports. On April 29, 2011 exceedances of PM10 NAAQS were recorded at all seven monitoring stations in Luna and Dona Ana County. All of the monitoring sites recorded extremely high PM10 concentrations and wind speeds. The Anthony monitor is the only site that did not record 18 m/s wind gusts. The following slides are a preliminary analysis of this event and include ideas of the type of information that may be presented in a EER demonstration.

2. Description of Event
A pacific cold front pushed through New Mexico with an area of Low pressure around the New Mexico/Colorado border. This creates a pressure gradient across the state, driving high winds at the surface to create blowing dust. This is the most frequent weather system that causes high winds capable of producing blowing dust. The other weather systems are cold fronts from the east (backdoor coldfront) , thunderstorm outflow fronts and dry or wet microbursts.

3. Temporal Extent and Source Areas of Event
All seven monitors in Dona Ana and Luna Counties recorded exceedances of the 24 hour average PM10 NAAQS indicating a large regional event. The red lines are the HYSPLIT back trajectory model runs and the number in parenthesis are the 24 hour average and max wind gust for the day. The back trajectories were calculated using NAM meteorological data beginning eight hours before the monitors recorded elevated levels of PM10. Notice all the lightly colored desert areas in the region that serve as emission sources. The back trajectories directly intersect some of these sources.

4. Exceptional Event?
This chart shows that the 24 hour average PM10 concentrations on April 29, 2011 were well above background levels. The historical 24 hour average PM10 data distributions do not include suspected exceptional event days. Suspected exceptional events are days that NMED submitted documentation and analysis under the NEAPs or EER.

5. Exceptional Event?
The hourly PM10 concentrations at the SPCY site dwarf historical hourly values. The top whisker represents the 95th percentile of data. The SPCY site is one of the longest running SLAMS sites and is located where El Paso, Cd. Juarez, and SLP meet.

6. Exceptional Event?
SPCY recorded a max wind gust of 22.6 m/s (50 mph). The highest wind gust recorded by NMED was 24.7 m/s (55mph) at Chaparral. Wind gusts are a better indicator of blowing dust than sustained hourly wind speeds. NMED considers 18 m/s (40 mph) the threshold that will create wind blown dust regardless of control measures and feels that very little documentation should be included in demonstrations. This chart shows that wind gusts exceeded the 95th percentiles for 12 hours (8am-8pm). This chart includes all hourly wind speed values including suspected high wind events since 2003.

7. Clear Causal Relationship?
This time series plot shows that as hourly average wind speed and max wind gust increase above 6 m/s and 11 m/s respectively, the concentration of PM10 also rises sharply. All sites exhibit this pattern.

8. Natural Event?
This image from GOES shows large dust plumes blowing throughout southern New Mexico, west Texas and northern Mexico. The source area for this event is the natural desert and not reasonably controllable.

9. No Exceedance but For Event
Anthony
SPCY
Chaparral
Holman DV WM
Deming
Max Hourly
2700
3629
3722
2023
921
1691
2204
2nd highest
1666
1907
896
1450
2195
3rd highest
836
1340
4th highest
767
5th highest
708
24 hour Average*
182
151
155
164
172
187
183
*24 hour Averages calculated using only the hours listed in the table. (i.e. SPCY 3629/24 = 151)
This table lists the highest hourly values recorded at each site. This shows that as little as one hour of a dust storm can cause an exceedance. An hourly value of 3700 µg/m3 will cause an exceedance by itself (3700/24 = 155).

10. Conclusions
High wind blowing dust event caused exceedances of the PM10 NAAQS (CCR, AAQ, Natural Event)
Event was not reasonably preventable or controllable (nRCP)
Recorded concentrations were well above background levels (HF)
The exceedances would not have occurred but for the event (NEBF)
This event meets the technical requirements of the EER and the data should be excluded when making attainment determinations.
Recommendations
1.) The requirements to exclude data under the EER can be excessive and burdensome for states with limited resources and well documented histories of naturally occurring high wind blowing dust events. The requirements should be determined on a case by case basis with the weight of evidence approach guiding demonstrations and concurrence. The is especially true in areas where few sources exist to cause high levels of pollution.