Protocol for the development of the Master Chemical Mechanism, MCM v3 (Part A): tropospheric degradation of non-aromatic volatile organic compounds

Abstract

Abstract. Kinetic and mechanistic data relevant to the tropospheric degradation of volatile organic compounds (VOC), and the production of secondary pollutants, have previously been used to define a protocol which underpinned the construction of a near-explicit Master Chemical Mechanism. In this paper, an update to the previous protocol is presented, which has been used to define degradation schemes for 107 non-aromatic VOC as part of version 3 of the Master Chemical Mechanism (MCM v3). The treatment of 18 aromatic VOC is described in a companion paper. The protocol is divided into a series of subsections describing initiation reactions, the reactions of the radical intermediates and the further degradation of first and subsequent generation products. Emphasis is placed on updating the previous information, and outlining the methodology which is specifically applicable to VOC not considered previously (e.g., α-and β-pinene). The present protocol aims to take into consideration work available in the open literature up to the beginning of 2001, and some other studies known by the authors which were under review at the time. Application of MCM v3 in appropriate box models indicates that the representation of isoprene degradation provides a good description of the speciated distribution of oxygenated organic products observed in reported field studies where isoprene was the dominant emitted hydrocarbon, and that the α-pinene degradation chemistry provides a good description of the time dependence of key gas phase species in α-pinene/NO X photo-oxidation experiments carried out in the European Photoreactor (EU-PHORE). Photochemical Ozone Creation Potentials (POCP) have been calculated for the 106 non-aromatic non-methane VOC in MCM v3 for idealised conditions appropriate to north-west Europe, using a photochemical trajectory model. The POCP values provide a measure of the relative ozone forming abilities of the VOC. Where applicable, the values are compared with those calculated with previous versions of the MCM.

Impacts of bromine and iodine chemistry on tropospheric OH and HO<sub>2</sub>: comparing observations with box and global model perspectives

“…The model includes recent updates to the chemistry scheme to include bromine chemistry (Parella et al, 2012;Schmidt et al, 2016) and iodine chemistry (Sherwen et al, 2016a, b). Sources of tropospheric bromine in the model include emissions of CHBr 3 , CH 2 Br 2 and CH 3 Br, and transport of reactive bromine from the stratosphere.…”

“…Sources of tropospheric bromine in the model include emissions of CHBr 3 , CH 2 Br 2 and CH 3 Br, and transport of reactive bromine from the stratosphere. Debromination of sea-salt aerosol is not included in the model following the work of Schmidt et al (2016), which showed better agreement with observations of BrO made by the GOME-2 satellite (Theys et al, 2011) and in the free troposphere and the tropical eastern Pacific MBL (Gomez Martin et al, 2013;Volkamer et al, 2015;Wang et al, 2015). Emission rates and bromine chemistry included in the model are described in detail by Parella et al (2012), with the bromine chemistry scheme described by 19 bimolecular reactions, 2 threebody reactions and 2 heterogeneous reactions using rate coefficients, heterogeneous reaction coefficients and photolysis cross sections recommended by Sander et al (2011).…”

“…In this work we use a chemistry scheme based on a subsection of the hydrocarbons (ethane, propane, iso-butane, n-butane, iso-pentane, n-pentane, hexane, ethene, propene, 1-butene, acetylene, isoprene, toluene, benzene, methanol, acetone, acetaldehyde and DMS) available from the Master Chemical Mechanism version 3.2 (MCM v3.2 http://mcm.leeds.ac.uk/MCM/home.htt) Saunders et al, 2003), with a halogen chemistry scheme described by Saiz-Lopez et al (2006), Whalley et al (2010) and Edwards et al (2011). We also include the reaction between OH and CH 3 O 2 (Bossolasco et al, 2014;Fittschen et al, 2014;Assaf et al, 2016;Yan et al, 2016), with a rate coefficient of 1.6 × 10 −10 cm 3 s −1 (Assaf et al, 2016) and products HO 2 + CH 3 O (Assaf et al, 2017), the impact of which on the HO 2 : OH ratio and CH 3 O 2 budget is described in the Supplement.…”

“…Halogen chemistry in the troposphere influences budgets of O 3 , HO x (OH and HO 2 ) and NO x (NO and NO 2 ) (von Glasow et al, 2004;Saiz-Lopez and von Glasow, 2012;Simpson et al, 2015;Schmidt et al, 2016;Sherwen et al, 2016a, b), affects the oxidation state of atmospheric mercury (Holmes et al, 2006(Holmes et al, , 2010, and impacts aerosol formation (Hoffmann et al, 2001;O'Dowd and Hoffmann, 2005;Mc-Published by Copernicus Publications on behalf of the European Geosciences Union. 3542 D. Stone et al: Impacts of bromine and iodine chemistry on tropospheric OH and HO 2 Figgans et al, 2004Figgans et al, , 2010Mahajan et al, 2011;Sherwen et al, 2016c).…”

Multi-generational oxidation model to simulate secondary organic aerosol in a 3-D air quality model

“…Finally, current schemes have not been tested against or constrained by measurements of multigenerational products (or classes of products) under realistic ambient conditions. Multi-generational VOC oxidation, in theory, can be explicitly modeled using detailed gas-phase chemical mechanisms such as the MCM (Master Chemical Mechanism; Jenkin et al, 2003;Saunders et al, 2003) or GECKO-A (Generator of Explicit Chemistry and Kinetics of Organics in the Atmosphere; Aumont et al, 2005;Camredon et al, 2007) and have been put to use to develop a better understanding of the reaction chemistry leading to SOA formation (Yee et al, 2012;Aumont et al, 2012;Valorso et al, 2011). However, these mechanisms track thousands to millions of chemical species and are computationally impractical for modeling multi-generational oxidation in 3-D models.…”