Origin, variability and age of biomass burning plumes intercepted during BORTAS-B

D. P. Finch, P. I. Palmer, M. Parrington

Research output: Contribution to journalArticlepeer-review

Abstract

We use the GEOS-Chem atmospheric chemistry transport model to interpret aircraft measurements of carbon monoxide (CO) in biomass burning outflow taken during the 2011 BORTAS-B campaign over eastern Canada. The model has some skill reproducing the observed variability (r = 0.45) but has a negative bias for observations below 100 ppb and a positive bias above 300 ppb. We find that observed CO variations are largely due to NW North American biomass burning, as expected, with smaller and less variable contributions from fossil fuel combustion from eastern Asia and NE North America. To help interpret observed variations of CO we develop an Eulerian effective age of emissions (A) metric, accounting for mixing and chemical decay, which we apply to pyrogenic emissions of CO. We find that during BORTAS-B the age of emissions intercepted over Halifax, Nova Scotia is typically 4–11 days, and on occasion as young as two days. We show that A is typically 1–5 days older than the associated photochemical ages inferred from colocated measurements of different hydrocarbons. We find that the median difference between the age measures (Δτ) in plumes (CH3CN > 150 ppt) peaks at 3–5 days corresponding to a chemical retardation of 50%. We find a strong relationship in plumes between A and Δτ (r2 = 0.60), which is not evident outwith these plumes (r2 = 0.23). We argue that these observed relationships, together with a robust observed relationship between CO and black carbon aerosol during BORTAS-B (r2 > 0.7), form the basis of indirect evidence that aerosols co-emitted with gases during pyrolysis markedly slowed down the plume photochemistry during BORTAS-B with respect to photochemistry at the same latitude and altitude in clear skies.
Original languageEnglish
Pages (from-to)13789-13800
JournalAtmospheric Chemistry and Physics
Volume14
Issue number6
DOIs
Publication statusPublished - 2014

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