December 20, 2012

Eric Massey

ADEQ, Air Quality

Dear Mr. Massey.

Your exceptional event documentation for July 3, 2011 was reviewed at the NRCD meeting today Dec.

20, 2012

Thank you for your work on this report. It does show the exceptional event that happened July 3, 2011.

We appreciate that you have made this statement for Yuma County.  

Unfortunately this is not the only exceptional event that has happened. We had another storm this last

summer that took out trees and did more that move PM10.

We look forward to our continued conservation about air quality and the effects of humidity,

temperature, and desert soils on air quality. As you know Yuma County and the agricultural community

would like to become an attainment area.  

Thank you for all of your work collecting data to make these demonstrations.

Yours truly,

Mark Kuechel  

Yuma NRCD

Sheryl Christenson

Laguna NRCD








 

Southern Regional Office 

400 West Congress Street  Suite 433  Tucson, AZ 85701 

(520) 628-6733 

Printed on rec

January 25, 2013 

Joy E. Herr-Cardillo 

Arizona Center for Law in the Public Interest 

2205 E. Speedway Blvd 

Tucson, AZ 85719 

RE: Response Submitted on January 1, 2013 to ADEQ Concerning the Request for Public 

Comments on the Exceptional Event Demonstration Packages for the Greater Phoenix Area 

Posted on December 3, 2012. 

Dear Ms. Herr-Cardillo; 

Thank you for reviewing and providing comments to these exceptional event demonstrations. 

We agree that ADEQ’s highest priority is to protect public health. Collectively, we have made 

great strides in improving the levels of PM10 in Maricopa County. 

Recently, we published our 25th Anniversary report. This report shows that the PM10 trend in 

Maricopa County has decreased by 40% over the last two decades due to the implementations of 

numerous control measures and cooperation with other air quality agencies and stakeholders. 

http://www.azdeq.gov/function/about/download/25th_anniversary_book-web.pdf

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Page 2 of 2 

Your letter also mentioned the study carried out by ASU, ADHS and ADEQ on PM10 

concentrations and asthma incidences. One of the recommendations, Chapter 8 Asthma Warning 

System, recommended ADEQ adopt a two part program; a predictive air pollution forecast 

system and an automated communications network that would advise the news media and 

citizens via phone, text and/or email with the daily air quality forecast. ADEQ has done just that 

and provides forecasts to Maricopa County (and products to Yuma, Nogales and Green Valley). 

We coordinate with Maricopa County’s Clean Air Make More, so that the ADEQ forecasts go 

directly to their website and subscribers, as well. Now, more than ever, citizens, mothers of 

asthmatic children, school nurses, or other school officials can get accurate and timely air quality 

forecast information sent directly to them on a daily basis. To subscribe go to: 

https://public.govdelivery.com/accounts/AZDEQ/subscriber/new

ADEQ has also implemented an Air Quality Flag program that can be used by schools to provide 

a visual indication of the air quality forecast to students, faculty and local residents. 

http://www.azdeq.gov/ceh/flag.html

Additionally, ADEQ’s Air Quality program adheres to the principles of ensuring conformity 

with EPA and ADEQ quality assurance programs, and submittal of the ambient air monitoring 

data to the Federal air quality database that is accessible to the public. 

The point of the exceptional event rule is to provide a means to carefully screen air quality data 

to ensure that events that overwhelm reasonable controls are accurately represented in all 

monitoring data and analysis. For the exceptional event days, these data are flagged in the EPA 

database. The exceptional event demonstrations provide EPA with an analysis and seek EPA’s 

concurrence that these events overwhelmed Best Available Control Measures (BACM) and Most 

Stringent Measures (MSM) already in place and that the exceedances are due to exceptional 

events that were beyond established controls at the time of the event. These demonstrations were 

prepared following the EPA guidance. They demonstrate that these events met the definition and 

criteria for exclusion as allowed in the Exceptional Event Rule, 40 CFR Parts 50 and 51. 

Attached are more specific responses to your comments. We appreciate your participation in this 

process and join you in the commitment to continue to protect public health for the citizens of 

Arizona. 

Sincerely, 

Eric C. Massey, Director 

Air Quality Division 
Comment 1

Comment: The demonstrations did not provide a reasonable degree of transparency about 

analytical methods so that independent reanalysis could be undertaken. 

Response: These demonstrations include a description of analytical method, specifically 

those including time series geographic information system (GIS) analysis. All other data 

included constitutes hourly average time series plots obtained from EPA’s Air Quality 

System (AQS) database or operating agency. 

EPA quality assurance procedures were followed with collection of all state and local 

ambient data included in the demonstration. ADEQ relies on National Weather Service 

(NWS) quality systems for meteorological data. 

ADEQ has the videos available to the public upon request in the event that a user is 

unable to open a link in the document. ADEQ has verified function of all video web links 

with the exception of one. The links provided in the August 25 through 28, 2011 

demonstration were incorrect and have been corrected in the final version. ADEQ has the 

videos available to the public upon request. The compression method used to create the 

videos aimed to provide both the best resolution possible and minimize file size so that 

users can readily obtain the files. 

ADEQ reviewed the draft documents and found two documents containing the statement 

that “additional documentation may be provided at a later date”. The statement refers to 

exceedances recorded outside of the Maricopa County non-attainment area, specifically 

Pinal County, during the same time period and further explains that theses exceedances 

may be addressed in a separate exceptional event submittal in the future and will be made 

available for public review at that time. 

ADEQ reviewed the comment and no additional changes to the demonstration are 

necessary. 

Comment 2

Comment: The demonstrations should be tested by modeling. 

Response: The exceptional event demonstrations rely on actual measured values 

including, particulate concentration and meteorological parameters. EPA guidance 

recommends that the agency use actual measured data to perform a demonstration that 

the events were exceptional in nature. The addition of model derived data into the 

analysis would not provide additional benefit in characterizing the events. Models are 

generally used to predict a future occurrence rather while actual measured data represent 

what did occur. Dust models, like those listed by the commenter, have not historically 

been capable of reproducing actual measured particulate concentrations and should be 

reserved for predictive exercises such as dust forecasting. ADEQ was unable to find the 

referenced modeling data on the commenter’s website and, therefore, is unable to provide 
further comment on its use. ADEQ reviewed the comment and no additional changes to 

the demonstration are necessary. 

Comment 3

Comment: The historical fluctuations are oversimplified. 

Response: The historical fluctuation analysis conducted for these demonstrations meet 

recommendations in the latest EPA guidance and have been approved as an appropriate 

method in past exceptional event requests submitted by ADEQ. The purpose of the historical 

analysis is to provide a comparison of the requested exceptional event day to past 

measurements. Its purpose is not to attempt to determine potential contributing sources on the 

exceedance day. The Conceptual Model and Clear Causal Relationship sections of the 

demonstration provide an explanation of the conditions during the event. ADEQ has 

determined that the Historical Fluctuation section clearly represents the specific exceedance 

day in the context of past measurements. ADEQ reviewed the comment and no additional 

changes to the demonstration are necessary. 

Comment 4

1st paragraph relating to the July 18, 2011 demonstration and timing of the South Phoenix 

winds, 17:50 arrival time of dust at South Phoenix and modeled surface friction velocity. 

Response: ADEQ is unable to verify the commenter’s suggestion that the demonstration 

specifies the impact at the South Phoenix monitor occurred precisely at 17:50. The South 

Phoenix site recorded a maximum hourly PM10 concentration of 2861μg/m3 during the 

1800 hour which corresponds to area maximum particulate concentrations provided in 

Table 5-2. The table illustrates area-wide PM10 concentrations, Sky Harbor winds and 

visibility. The plot clearly shows a wind speed increase between 1700 and 1800 and a 

corresponding PM10 increase and visibility decrease. The radar derived proximity of the 

storm cell to the Phoenix area, approximately 25 miles south south-east as noted by the 

commenter, is not a clear indicator of the position of the storm outflow. In this event the 

outflow arrived ahead of the thunderstorm as evident in the details provided in the 

exceptional event demonstration. ADEQ reviewed the comment and no additional 

changes to the demonstration are necessary. 

2nd paragraph relating to the method of subtracting the Glendale monitor value from the 

South Phoenix value and suggestion that Glendale represents overall dust storm impacts. 

Response: The process of subtracting one area monitor from another is not an appropriate 

methodology for evaluating region-wide dust storm events. Further, ADEQ disagrees that 

the Glendale site represents overall dust storm impacts. The impact of the outflow dust is 

evident at nearly all Phoenix area PM10 monitors although the magnitude varies from 

site to site. This variability is described in the exceptional event document and is 

attributed to an influx of particulate matter from outside the non-attainment boundary and 

the contribution of local sources where local controls were overwhelmed. ADEQ 

reviewed the comment and no additional changes to the demonstration are necessary. 
3rd paragraph relating to the arrival of dust impacts at South Phoenix at 17:50, local dust 

sources already increasing PM10 ant South Phoenix but not Glendale, and video of dust 

devils at South Phoenix well before 17:50. 

Response: ADEQ is unable to verify the commenter’s suggestion that the demonstration 

specifies the impact at the South Phoenix monitor occurred precisely at 17:50. The 

visibility videos show, as do hourly measurements, an earlier, less intense, dust cloud 

moving through the area at approximately 1600 and 1700. ADEQ reviewed the comment 

and no additional changes to the demonstration are necessary. 

4th paragraph relating to ADEQ’s claims that the Buckeye exceedance is very rare and in 

the 99.5 percentile while 10 other values are above 99.5 percentile (9 during summer 

months 1 in November). 

Response: This is the purpose of the historical fluctuations analysis, to provide the past 

maximum PM10 data so this event can be compared to the historical record and show the 

extent to which it varies from the norm. ADEQ reviewed the comment and no additional 

changes to the demonstration are necessary. 

Comment 5

Comment: The August 25, 2011 through August 28, 2011 demonstrations rely on 

recorded wind speeds of 30 mph at Mesa Williams airport (p. 40), however these data are 

marked as suspect by NCDC. 

Response: The data does have an “s” flag. But it does not mean the value is erroneous. 

According to Appendix L: Hourly Data Quality Control Document, of the NCDC 

Technical Document, one test as a part of the automated QA/QC process involves a 

“check to see if the wind speed has increased or decreased by more that 20 knots from the 

average of previous and following hourly observations”. If the change is greater than 20 

knots, a flag will be placed on the data. We believe this is what occurred in reference to 

the “s” flag placed on the 30 mph reading at the Mesa Williams airport station. A wind 

speed of 5 mph was recorded before and 9 mph was recorded after the 30 mph reading. 

 The suspect flag was likely placed on the data as part of the automated QA/QC process 

due to the sudden onset, and subsequent sudden decrease, in winds. Such sudden wind 

increases are not uncommon during the Arizona Monsoon due to the generation and 

propagation of outflow boundaries. These outflows can cause sudden increases in winds 

that can be very short lived, which would account for the short-term high wind reading 

and subsequent data flag. Additional high winds were reported in other parts of Maricopa 

and Pinal Counties including upwind at Casa Grande Municipal Airport, which saw 

sustained winds above 20 mph with gusts to 25 mph within the hour of, but preceding, 

the 30 mph report at Mesa Williams. The NCDC QA Rules Effective January, 2005 

state:1) flags will be available for most data elements if data are suspect, 2) ‘s” will be 

appended to the value on the web form or in a column following the suspect value in the 
ASCII form, and 3) if data are flagged as erroneous, it will not be printed. ADEQ 

reviewed the comment and no additional changes to the demonstration are necessary. 

Comment 6

Comment: The public notice period is inadequate. 

Response: There is no specific timeframe provided in the Exceptional Event Rule, 40 

CFR 50.14(c)(3), only that an opportunity is provided for public comment. 

Submission of demonstrations.(i) A State that has flagged data as being due to an exceptional event and is 

requesting exclusion of the affected measurement data shall, after notice and opportunity for public comment, 

submit a demonstration to justify data exclusion to EPA. 

ADEQ typically provides a 30 day comment period from the public for review of data 

and proposed actions by ADEQ, which was done for these demonstrations.