*PLEASE SEE 6/21/10 UPDATE AT BOTTOM OF DOCUMENT

To: Chemical Speciation Network (CSN) Data Users

Subject: Update to historical CSN Carbon Data

Date: 03/05/2010

An error has been detected in a recent recalculation of elemental and organic carbon data collected by the CSN. This error affects how carbon data are partitioned between organic and elemental carbon for samples collected on and before July 7, 2003. Specific details follow:

• The data affected are the organic and elemental carbon data collected for the CSN on and before July 7, 2003. The error affects field and trip blank data, as well as routine sample data.

  • The parameter code for Elemental Carbon (EC) is 88307 o The parameter code for Organic Carbon (OC) is 88305

• EC and OC data with this error were uploaded to AQS on September 23, 2009.

• Please disregard EC/OC data associated with samples on or before July 7, 2003 if retrieved from the following web sites between September 23, 2009 and February 25, 2010: o AQS;

  • The “Obtaining AQS Data” web site at: http://www.epa.gov/ttn/airs/airsaqs/detaildata/; o Or the AQS Data Mart at: http://www.epa.gov/ttn/airs/aqsdatamart/access/interface.htm

• Data downloaded from AirExplorer (http://www.epa.gov/airexplorer/) have not been updated with the errors and still include the original EC/OC calculations.

We have identified the error and removed the incorrect data from AQS and the Data Mart. EPA will recalculate the data with the correct partition between EC and OC. This new dataset is being prepared and should be reloaded into AQS and other data web sites by the end of March 2010. We will provide a listserve notice when the correct data are available*.

Please contact either David Shelow (shelow.david@epa.gov) or Tim Hanley (hanley.tim@epa.gov) with any questions.

Background:

In order to improve consistency in the data generated for the entire CSN data collection period from 2000 to current, EC/OC data collected prior on or before July 7, 2003 were recalculated with the new version of analysis instrument software that was introduced in 2003. Unfortunately, unexpected errors were introduced during the recalculation process. The planned revisions are intended to correct these errors.

The decision to recalculate EC/OC data was made, in part, based on recommendations from a January 2324, 2008 Carbon Analysis Workshop that was held in Davis California. In that workshop, EPA and other stakeholders from the CSN and IMPROVE networks met to discuss improvements to the carbon data from the IMPROVE and CSN programs that would achieve better consistency between the programs.

* UPDATE (6/21/10) - EPA has recalculated the data with the correct partition between EC and OC. The new dataset has been reloaded into AQS and other data web sites.