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1 Collocated STN-CSN and IMPROVE carbon measurements WHW, UCD 1/22/08

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2 IMPROVE analytical upgrade

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3 EXPECTIONS & WORKING ASSUMPTIONS analysis : Analytical methods agree for TC = OC + EC: TC CSN = TC IMP i.e., carbon itself is measured unambiguously. The relationship between the splits is linear and homogeneous: OCOC measured OC measured = (1-f)OC + gEC ECEC measured EC measured = fOC + (1-g)EC IMPROVEs f and g may differ between old and new TOR analyses.

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4 EXPECTATIONS & WORKING ASSUMPTIONS sampling : The collected sample may be affected by filter artifacts (FA) and sampling artifacts (SA): C = (1-B SA )[C]V + A FA,B SA > 0 and A FA > 0 The filter and sampling artifacts for EC are negligible in both networks: EC = [EC]V (B SA = 0 and A FA = 0) These assumptions lead us to expect an unadjusted value (reported by CSN) of: TC/V = OC/V + EC/V = (1-B SA )[OC] + A FA /V + [EC] = [TC] B SA [OC] + A FA /V

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5 EC Each point is the median from all observations on days -3, 0, +3 by the indicated sampler. Out-of-range points are always plotted at the appropriate boundary.

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6 TC Note the switch from IMPROVE / CSN to CSN / IMPROVE. (Both plots show the larger measurement on top.) inverse of previous ratio

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7 TC Neither ratio nor difference is quite right for a relationship of the form [CSN] = a + b[IMPROVE]. difference, not ratio

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8 For EC, the systematic differences between CSN and IMPROVE, and between old and new IMPROVE, seem to be multiplicative.

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9 For TC, the difference between CSN and IMPROVE appears to include an additive offset in addition to a multiplicative factor. There is no obvious difference between old and new IMPROVE.

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10 2005-6 For EC, the difference between CSN and IMPROVE shows little dependence on the CSN sampler, suggesting that it is mainly analytical.

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11 2005-6 For TC, the difference between CSN and IMPROVE clearly does vary with the CSN sampler.

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12 2005-6 Site-specific differences between CSN and IMPROVE are evident only at Phoenix, where the MetOne - IMPROVE TC difference tends to be higher than it is elsewhere.

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13 Phoenix, 2004-6 A collocated IMPROVE monitor has operated at Phoenix since March 2004. These plots compare the two collocations on days with observations from both. Nothing out of the ordinary is evident.

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14 IMPROVE analytical upgrade

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15 RECALL OUR WORKING ASSUMPTION : TC/V = [TC] B SA [OC] + A FA /V (i) The MetOne face velocity (6.7 L/min through a 47 mm filter) is much lower than the IMPROVE face velocity (~22.8 L/min through a 25 mm filter). (ii) Reported IMPROVE concentrations are corrected for the filter artifact. It will simplify our interpretation if we accordingly neglect (i) the MetOne sampling artifact and (ii) the IMPROVE filter artifact. Then [TC] IMP = [TC] B IMP [OC] and[TC] CSN = [TC] + A CSN /V MetOne. Solving for [TC] in both expressions and equating the two solutions yields [TC] CSN = [TC] IMP + B IMP [OC] + A CSN /V MetOne Estimate OC: ~ [TC] IMP + B IMP *[OC] IMP + A CSN /V MetOne = [EC] IMP + (1+B IMP *)[OC] IMP + A CSN /V MetOne

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16 EXPECTATION : [TC] CSN = [EC] IMP + (1+B IMP *)[OC] IMP + A CSN /V MetOne OLS REGRESSION: [TC] CSN = (1+b EC )[EC] IMP + (1+b OC )[OC] IMP + a 1 ++ a 12 + e 2005-6 observations at 7 MetOne sites (excluding Phoenix): b EC = 0.008 (+/-0.05) no sampling artifact for IMPROVE EC b OC = 0.22 (+/-0.03) ~ 20% sampling loss for IMPROVE OC rms(e) = 0.9 ug/m 3 (r 2 = 0.986, n = 779) a mm next slide

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17 MetOne artifacts

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18 OLS REGRESSION FOR EC: [EC] CSN = (1-g)[EC] IMP + f[OC] IMP + a 1 ++ a 12 + e 2005-6 observations at 7 MetOne sites (excluding Phoenix): g = 0.40 (+/-0.02) f = 0.03 (+/-0.01) rms(e) = 0.3 ug/m 3 (r 2 = 0.942, n = 779) a mm : mixed signs, marginal significance

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19 REVIEW OF EVIDENCE FOR DIFFERENCES: Observed differences Changed at 2004 2005 TOR transition Vary with CSN sampler Suggest a seasonally varying additive artifact in CSN OC (relative to IMPROVE) Suggest a multiplicative negative artifact in IMPROVE OC (relative to CSN)

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21 The 779 MetOne observations from 2005-6 at seven sites can be linearly transformed into IMPROVE values with rms errors of EC: 0.4 ug/m 3 (27% of mean value) TC: 0.8 ug/m 3 (16% of mean value)