1 CONTINUITY OF IMPROVE CARBON DATA THROUGH THE 1 JANUARY 2005 INTRODUCTION OF NEW ANALYTICAL INSTRUMENTATION* WHW, 10/2/07 *Chow et al. (2007) JA&WMA 57: updated 1/23/08 This is an updated and elaborated version of a presentation sent to DRI in August 2007 and presented at the IMPROVE Steering Committee meeting in Durango ( ). It applies to carbon data some of the analytical techniques developed at CNL to identify temporal instabilities in XRF data. The plots that follow are snapshots from early stages of a hypothesis-generating exploration, and at this point are intended only for internal discussions of their interpretation.

2 We begin with time series of the ratios TOR fraction / total carbon (g/g or mol/mol). VIEWS “raw”, downloaded 9/07 VIEWS “preliminary”, downloaded 9/07 (Babs is not included in VIEWS preliminary data, and so was obtained from CNL’s internal files.)  Scales vary from fraction to fraction, but grid intervals remain constant (as a visual cue to the differences).

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4 MEDIAN AND INTERQUARTILE RANGE ENTIRE NETWORK, ALL VALID DATA “NORMAL”: for each week {1,2,…,52}, the median of 24h medians from that week during

5 MEDIAN AND INTERQUARTILE RANGE ENTIRE NETWORK, ALL VALID DATA unsynchronized sampling during 2/week  1/3day transition: data excluded version 1 | version 2 samplers IMPROVE IMPROVE_A (DRI/OGC) (DRI Model 2001)

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17 Some organic fractions changed abruptly on 1 January 2005.

18 Others seemed to anticipate the change in instrumentation.

19 The changes in OC and EC are neither abrupt nor dramatic, but the greater regularity of these aggregates makes them noticeable. Winter also appears anomalous.

20 We have focused on carbon/carbon ratios up to now. Total organic carbon, OC, can also be compared against non- sulfate hydrogen. This is calculated from the A-module PESA measurement of H and the B-module IC measurement of SO 4 = on the assumption that all sulfate is ammonium sulfate. On the further assumption that ammonium sulfate accounts for all inorganic hydrogen, non-sulfate hydrogen is referred to as organic hydrogen, OH. Total elemental carbon, EC, can be compared against the A- module HIPS (hybrid integrating plate/sphere) measurement of light absorption. These data are submitted by CNL as LRNC (the “NC” stands for non-corrected), and delivered by VIEWS as Babs in the non-standard units (10 8 m) -1. Of course, each measurement added to the comparisons also carries its own errors and uncertainties.

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22 mol/mol mol/mol MEDIAN AND INTERQUARTILE RANGE ENTIRE NETWORK, ALL VALID DATA The new measurements report less OC, not only relative to TC, but also relative to OH – estimated wholly independently. Like OP/TC, OC/OH seemed to anticipate the instrumentation change.

23 MEDIAN AND INTERQUARTILE RANGE ENTIRE NETWORK, ALL VALID DATA m 2 /g g/10m 2

m 2 /g MEDIAN AND INTERQUARTILE RANGE ENTIRE NETWORK, ALL VALID DATA g/10m 2 EC/LRNC trended higher in 2005 than in 2004, but gaps leave the record somewhat ambiguous.

25 MEDIAN AND INTERQUARTILE RANGE ENTIRE NETWORK, ALL VALID DATA Comparison with gravimetric fine mass, considered one of the most reliably accurate of the measurements, gives no clear indication that TC = EC+OC did exhibit any decrease in 2005.