Constraining a hybrid volatility basis-set model for aging of wood-burning emissions using smog chamber experiments: a box-model study based on the VBS scheme of the CAMx model (v5.40)

Giancarlo Ciarelli,Sebnem Aksoyoglu,Imad El Haddad,Ottmar Möhler,André S H Prévôt,Urs Baltensperger,Emily Bruns

doi:10.5194/gmd-10-2303-2017

Abstract

Abstract. In this study, novel wood combustion aging experiments performed at different temperatures (263 and 288 K) in a ∼ 7 m3 smog chamber were modelled using a hybrid volatility basis set (VBS) box model, representing the emission partitioning and their oxidation against OH. We combine aerosol–chemistry box-model simulations with unprecedented measurements of non-traditional volatile organic compounds (NTVOCs) from a high-resolution proton transfer reaction mass spectrometer (PTR-MS) and with organic aerosol measurements from an aerosol mass spectrometer (AMS). Due to this, we are able to observationally constrain the amounts of different NTVOC aerosol precursors (in the model) relative to low volatility and semi-volatile primary organic material (OMsv), which is partitioned based on current published volatility distribution data. By comparing the NTVOC ∕ OMsv ratios at different temperatures, we determine the enthalpies of vaporization of primary biomass-burning organic aerosols. Further, the developed model allows for evaluating the evolution of oxidation products of the semi-volatile and volatile precursors with aging. More than 30 000 box-model simulations were performed to retrieve the combination of parameters that best fit the observed organic aerosol mass and O : C ratios. The parameters investigated include the NTVOC reaction rates and yields as well as enthalpies of vaporization and the O : C of secondary organic aerosol surrogates. Our results suggest an average ratio of NTVOCs to the sum of non-volatile and semi-volatile organic compounds of ∼ 4.75. The mass yields of these compounds determined for a wide range of atmospherically relevant temperatures and organic aerosol (OA) concentrations were predicted to vary between 8 and 30 % after 5 h of continuous aging. Based on the reaction scheme used, reaction rates of the NTVOC mixture range from 3.0 × 10−11 to 4. 0 × 10−11 cm3 molec−1 s−1. The average enthalpy of vaporization of secondary organic aerosol (SOA) surrogates was determined to be between 55 000 and 35 000 J mol−1, which implies a yield increase of 0.03–0.06 % K−1 with decreasing temperature. The improved VBS scheme is suitable for implementation into chemical transport models to predict the burden and oxidation state of primary and secondary biomass-burning aerosols.

Highlights

The fact that some semi-volatile compounds can exist in either gaseous or particulate form results in considerable uncertainties in the emission inventories for primary organic aerosol (POA)
The amount of OMbsv [μg m−3] (NTVOCs) / (OMsv) was varied until the measured POA mass at t = 0 (OAt=0) was reached and the resulting non-traditional volatile organic compounds (NTVOCs) / OMsv was calculated for the different experiments
Hvap = {70 000 − 11 000 × log(C∗)} J mol−1 shall be used in combination with OMsv.Vol.distREF as model inputs and in Sect. 6 we assess the sensitivity of the resulting NTVOCs / OMsv ratios and secondary organic aerosol (SOA) formed on the chosen OMsv.Vol.dist

Summary

Introduction

The fact that some semi-volatile compounds can exist in either gaseous or particulate form results in considerable uncertainties in the emission inventories for primary organic aerosol (POA). Fountoukis et al (2014) were among the first to implement the VBS approach into a large-scale aerosol model, following the multiple distribution framework approach proposed by Tsimpidi et al (2010) They found that the approach considerably improved the model result for OA when compared to a range of observations from the EUCAARI field campaign (Kulmala et al, 2009, 2011) and from EMEP monitoring network (Tørseth et al, 2012). Bergström et al (2012) used the EMEP model for the period of 2002–2007 to compare different partitioning and aging schemes Their results indicate the importance, potential underestimation, of wood-burning emissions in Europe, in line with other studies (Kostenidou et al, 2013; Fountoukis et al, 2016; Tsimpidi et al, 2016). Most uncertain parameters namely enthalpies of vaporization of SOA, NTVOCs (non-traditional volatile organic compounds) reaction rates and their yields were investigated by means of a brute force approach, and a best-fitting solution, within acceptable physical limits and error ranges, was retrieved

Experimental method

Model description

Parameterization methodology

Results

Wood-burning aging at low and high temperatures

Discussions and major conclusions