Data Quality

Subtle, long-term progress requires top-notch data

The goal of the U.S. EPA’s 1999 Regional Haze Rule is to return visibility to natural levels in most of the nation’s national parks and wilderness areas by the year 2064. With this 65-year timeframe, incremental changes that occur during the rule’s 5-year study periods can be so subtle that distinguishing real change from background noise requires data of the highest caliber and reliability.

To this end, data exploration and uncertainty assessment are vital components of Crocker Nuclear Laboratory’s air quality research program.

The research team conducts multiple levels of quality assurance and control on its aerosol samplers and data. At the same time, the team devotes its research to improving every aspect of the IMPROVE program. These efforts include developing better methods to test and calibrate the program’s instrumentation; developing advanced techniques for particulate analysis; identifying and characterizing the causes of data trends; and developing improved tools for monitoring data quality while promptly identifying measurement problems. (See IMPROVE research.)

IMPROVE data reported uncertainty and minimum detection limit (MDL)

Each reported concentration is accompanied by its calculated uncertainty and minimum detection limit (MDL). The procedures for calculating these values are described in the IMPROVE Data Processing and Validation SOP #351, Section 5.3. When downloading IMPROVE data from the FED website, check "Uncertainty" and "Min. Detection Limit" in the "Fields" tab if you would like to receive these values along with the concentration data.

Collocated measurements

Beginning in 2003 IMPROVE began collocated measurements at selected sites. At these sites, the Crocker team added a fifth sampling module to the aerosol sampler. By comparing data from this module with its pair in the sampler, we can obtain an overall estimate of uncertainty from all sources. Data analysts at UC Davis have developed advanced procedures that allow these collocated data to be used to estimate the uncertainty in the reported concentrations. When downloading IMPROVE data from the FED website IMPROVE Data Access, check "POC" in the "Fields" tab to receive an indicator of a collocated module. Collocated data are designated as POC=2.

Data advisories

Data advisories are archived on the IMPROVE website to document interesting findings from the IMPROVE database including data anomalies, potential problems, and new uses for the IMPROVE data. Many of these data advisories have been written by IMPROVE staff at UC Davis to describe changes or anomalies that we have encountered.