Carbon Artifact Adjustment in IMPROVE Lowell Ashbaugh Crocker Nuclear Lab University of California, Davis January 22, 2008

Sampling Artifacts for Particulate Carbon Passive positive artifact Passive positive artifact Quartz filter adsorbs volatile organic gases passively upon exposure to the atmosphere without airflow Quartz filter adsorbs volatile organic gases passively upon exposure to the atmosphere without airflow Active positive artifact Active positive artifact Quartz filter adsorbs volatile organic gases during sampling Quartz filter adsorbs volatile organic gases during sampling Active negative artifact Active negative artifact Volatile organic particles dissociate into gases during sampling and are lost to the filter Volatile organic particles dissociate into gases during sampling and are lost to the filter

Result of Artifact on Secondary Filter (CS) Passive positive artifact Passive positive artifact CS = CP → Subtract CS from CP CS = CP → Subtract CS from CP Active positive artifact Active positive artifact CS = fraction of CP → Subtract CS/(1-eff) from CP CS = fraction of CP → Subtract CS/(1-eff) from CP Active negative artifact Active negative artifact CS = “lost” VOP from CP → Add CS to CP CS = “lost” VOP from CP → Add CS to CP

IMPROVE OC Measurements IMPROVE assumes all positive artifact IMPROVE assumes all positive artifact CP – quartz front filter CP – quartz front filter CS – quartz backup filter (median of monthly values from 6 sites) CS – quartz backup filter (median of monthly values from 6 sites) Particulate OC = CP – CS Particulate OC = CP – CS Field blanks Field blanks All sites All sites A few each year A few each year No air flow through blanks No air flow through blanks In sampler for 7 days In sampler for 7 days Supported by research Supported by research D. Fitz (1990), AS&T 12: D. Fitz (1990), AS&T 12:

IMPROVE sites with CS filters

Time history of carbon artifacts

Histograms for July 2005

Monthly CS measurements by site