CollocatedSTN-CSN and IMPROVEcarbon measurements

WHW, UCD 1/22/08

IMPROVE analytical upgrade

EXPECTIONS & WORKING ASSUMPTIONS analysis:

Analytical methods agree for TC = OC + EC:TCCSN = TCIMPi.e., carbon itself is measured unambiguously.

The relationship between the splits is linear and homogeneous:OCOCmeasuredOCmeasured = (1-f)OC + gEC ECECmeasuredECmeasured = fOC + (1-g)ECIMPROVEs f and g may differ between old and new TOR analyses.

EXPECTATIONS & WORKING ASSUMPTIONS sampling:The collected sample may be affected by filter artifacts (FA) and sampling artifacts (SA):C = (1-BSA)[C]V + AFA,BSA > 0 and AFA > 0The filter and sampling artifacts for EC are negligible in both networks:EC = [EC]V (BSA = 0 and AFA = 0)

These assumptions lead us to expect an unadjusted value (reported by CSN) of: TC/V = OC/V + EC/V= (1-BSA)[OC] + AFA/V + [EC]= [TC] BSA[OC] + AFA/V

ECEach point is the median from all observations on days -3, 0, +3 by the indicated sampler.

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

TCNeither ratio nor difference is quite right for a relationship of the form [CSN] = a + b[IMPROVE]. difference, not ratio

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

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.

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

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

2005-6Site-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.

Phoenix, 2004-6A 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.

IMPROVE analytical upgrade

RECALL OUR WORKING ASSUMPTION: TC/V = [TC] BSA[OC] + AFA/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] BIMP[OC]and[TC]CSN = [TC] + ACSN/VMetOne.Solving for [TC] in both expressions and equating the two solutions yields [TC]CSN = [TC]IMP + BIMP[OC] + ACSN/VMetOneEstimate OC: ~ [TC]IMP + BIMP*[OC]IMP + ACSN/VMetOne = [EC]IMP + (1+BIMP*)[OC]IMP + ACSN/VMetOne

EXPECTATION:[TC]CSN = [EC]IMP + (1+BIMP*)[OC]IMP + ACSN/VMetOneOLS REGRESSION:[TC]CSN = (1+bEC)[EC]IMP + (1+bOC)[OC]IMP + a1 ++ a12 + e2005-6 observations at 7 MetOne sites (excluding Phoenix):bEC = 0.008 (+/-0.05)no sampling artifact for IMPROVE ECbOC = 0.22 (+/-0.03)~ 20% sampling loss for IMPROVE OCrms(e) = 0.9 ug/m3(r2 = 0.986, n = 779)amm next slide

MetOne artifacts

OLS REGRESSION FOR EC:[EC]CSN = (1-g)[EC]IMP + f[OC]IMP + a1 ++ a12 + e2005-6 observations at 7 MetOne sites (excluding Phoenix):g = 0.40 (+/-0.02)f = 0.03 (+/-0.01)rms(e) = 0.3 ug/m3(r2 = 0.942, n = 779)amm: mixed signs, marginal significance

REVIEW OF EVIDENCE FOR DIFFERENCES:

Observed differencesChanged at 2004 2005 TOR transitionVary with CSN samplerSuggest a seasonally varying additive artifact in CSN OC (relative to IMPROVE)Suggest a multiplicative negative artifact in IMPROVE OC (relative to CSN)

The 779 MetOne observations from 2005-6 at seven sites can be linearly transformed into IMPROVE values with rms errors ofEC: 0.4 ug/m3 (27% of mean value)TC: 0.8 ug/m3(16% of mean value)