Carbon Measurements and Adjustments Measurement of organics by IMPROVE & STN networks, Use of blank data to correct carbon concentration measurements, Planned changes by EPA, Implications for continuity in longitudinal analyses Neil Frank USEPA/OAQPS For presentation at Air Quality Data in Health Effects Research Nov 30 – Dec 1, 2006

2 Carbon Measurements by STN and IMPROVE Factors that affect estimated ambient carbon concentrations Analytical protocol (thermal optical technique) –STN: NIOSH-type TOT method, OC/EC and 4 OC sub-fractions –IMPROVE: DRI TOR method, OC/EC, 5 OC and 3 EC sub-fractions Collection device (field samplers) –Quartz filters without denuders –Different flow rates, face velocity and different artifacts Sampler location (rural vs urban and intra-urban) Data Reporting (& adjustments) –STN (2001- ) AQS: without blank or other adjustments, field blanks after 2003 Air Explorer web site: with adjustments – –IMPROVE (1990- ) VIEWS web site: with adjustments –

3 Carbonaceous concentrations from measured C can be a very uncertain calculation Many sources of error beyond analytical uncertainty Blank correction, b, to adjust for sampling artifacts –STN network uses different samplers & without backup filters Avg value derived from field blanks provides a crude estimate –can result in negative daily values Adjustments vary among 4 different EPA urban speciation samplers (Most are MetOne) Large field blank variability may not justify site or seasonal adjustments These network values are in same ballpark as intercept of regressing OC vs. PM2.5 The above values are used to adjust OC measurement data on Air Explorer and in EPA analyses –IMPROVE: OC artifact adjustments are relatively small (on average, ~ ug/m3) –Sampler has smaller filter, higher flow rate and uses backup filters Blank adjusted using monthly network median backup filter by carbon fraction * Network-wide values from data as reported by RTI Recent investigations reveal changes after 2003 (see next slide)

4 Trends in STN field blank levels should be considered Since 2002, STN field and trip blanks values for Met One (SASS) and Anderson (RAAS) samplers have decreased 33% and values for URG (MASS) samplers have increased 25%. Reasons for the changes are not known at this time. Preliminary Average Total Carbon Blank by Year, ug/m3 (subset of sites with long-term data) Met One Field & Trip Blanks (Data from RTI and AQS.) Most prevalent Most like IMPROVE flowrate

5 Carbon Mass is Different than Measured Carbon Total Carbonaceous Mass (TCM) is generally defined as k*(OC-b)+EC Mass multiplier, k, varies with aerosol type and mix –1.6 ± 0.2 (urban) –2.1 ± 0.2 (rural) [Weighted average needed for mixed urban/regional aerosol] –2.4 ± 0.2 (smoke) –Turpin's above estimates (2001) are based on limited OC speciation data –1.4 has been used for IMPROVE and STN. New IMPROVE algorithm uses 1.8 Uncertainty in k is ~ + 33% (relative to 1.8) Multiplier may also depend on –Analytical protocol More OC with STN than IMPROVE and there is no extra mass assigned to “EC” –Selection of blank adjustment, “b,” and any unaccounted for concentration related sampling artifacts Other sources of uncertainty: Retained carbon mass on FRM Teflon – Volatile or other OC may pass thru Teflon FRM has higher face velocity than many STN samplers –Water [20-24% of measured PM2.5 water is assigned to C] –Therefore, other adjustments are needed to represent retained FRM mass

6 Inferred FRM Carbon using "SANDWICH“ Sulfate, Adjusted Nitrate, Derived Water, Inferred Carbonaceous mass Hybrid material balance approach Total Carbonaceous Mass by material balance: TCM mb = PM { [SO4] + [NO3 FRM ] +[NH4] +[water] + [Crustal] + [FRM blank] } Other PM 2.5 constituents eg. salt, could also be considered Water and reduced FRM NO3 are estimated by models. OCM mb = [TCM mb] – [EC] TCM mb explicitly accounts for positive and negative sampling artifacts, OC hydration, and mass multipliers for carbonaceous material retained on FRM Teflon. TCM mb is upper estimate for TCM and is subject to error in non-C components. This approach has been used by EPA for regulatory modeling SANDWICHed PM2.5 ( ) representing what may have been measured by the FRM are available on Air Explorer Reference: Frank, N. Retained Nitrate, Hydrated Sulfates, and Carbonaceous Mass in Federal Reference Method Fine Particulate Matter for Six Eastern U.S. Cities, J. Air & Waste Manage. Assoc. 56: 500–511 (2006)

7 TCMmb tracks 1.4*(OC-b) reasonably well Displays similar seasonal pattern but different trends for some regions Regional quarterly averages and annual trend lines are shown TCM mb TCM 1.4 (old blank) Industrial MidWest, 11 sites Northeast, 10 sites Southeast, 11 sites TCM mb TCM 1.4 (old blank) TCM 1.4 (old blank) TCM mb For these comparisons, blank values “b”, were derived from the RTI report

8 Regional average values of TCM m b agree well with 1.4*(OC-b) and year-specific b values - 3 rd quarter deviation in SE may reflect SOA (need higher “k”) The successful choice of k (e.g. 1.4) to represent retained FRM mass (on Teflon) may depend on the selected value for “b”. The value for “k” may also depend on the particular thermal analytical technique and OC-EC split. Recognize that carbon adjustments are uncertain and multiple approaches may be needed Better agreement with year-specific field blanks TCMmb can help validate choice of “fudge” factors (k and b) and can provide continuity for longitudinal studies TCM mb Industrial MidWest, 11 sites TCM 1.4 (yrly blank) Northeast, 10 sites Southeast, 11 sites TCM mb TCM 1.4 (yrly blank) TCM 1.4 (yrly blank)

9 Next Steps New STN carbon protocol –For national consistency in ambient carbon monitoring, EPA is switching the STN carbon protocol to the IMPROVE method. STN’s new IMPROVE-like samplers (22 Lpm flow rate) to be phased in over three years will also likely have less carbon sampling artifact than current STN data from SASS and RAAS samplers. –Health study and NA cities are in phase I implementation Development of new procedures to adjust carbon measurements for sampling artifacts –EPA has funded Chow and Watson to recommend procedures to estimate sampling artifact for the new urban samplers (e.g. using backup filters) and to develop appropriate factors for estimating historical STN OCM and EC consistent with the future measurements. –EPA has funded Warren White to define total uncertainty (incl. blanks) –Findings are expected Spring 2007 Carbon trends during transition period –EPA will be using TCMmb to describe trends until appropriate carbon adjustments and comparability can be established between the old STN and new urban-IMPROVE carbon protocols.