Future changes in isoprene-epoxydiol-derived secondary organic aerosol (IEPOX SOA) under the Shared Socioeconomic Pathways: the importance of physicochemical dependency

Abstract. Secondary organic aerosol (SOA) is a dominant contributor of fine particulate matter in the atmosphere, but the complexity of SOA formation chemistry hinders the accurate representation of SOA in models. Volatility-based SOA parameterizations have been adopted in many recent chemistry modeling studies and have shown a reasonable performance compared to observations. However, assumptions made in these empirical parameterizations can lead to substantial errors when applied to future climatic conditions as they do not include the mechanistic understanding of processes but are rather fitted to laboratory studies of SOA formation. This is particularly the case for SOA derived from isoprene epoxydiols (IEPOX SOA), for which we have a higher level of understanding of the fundamental processes than is currently parameterized in most models. We predict future SOA concentrations using an explicit mechanism and compare the predictions with the empirical parameterization based on the volatility basis set (VBS) approach. We then use the Community Earth System Model 2 (CESM2.1.0) with detailed isoprene chemistry and reactive uptake processes for the middle and end of the 21st century under four Shared Socioeconomic Pathways (SSPs): SSP1–2.6, SSP2–4.5, SSP3–7.0, and SSP5–8.5. With the explicit chemical mechanism, we find that IEPOX SOA is predicted to increase on average under all future SSP scenarios but with some variability in the results depending on regions and the scenario chosen. Isoprene emissions are the main driver of IEPOX SOA changes in the future climate, but the IEPOX SOA yield from isoprene emissions also changes by up to 50 % depending on the SSP scenario, in particular due to different sulfur emissions. We conduct sensitivity simulations with and without CO2 inhibition of isoprene emissions that is highly uncertain, which results in factor of 2 differences in the predicted IEPOX SOA global burden, especially for the high-CO2 scenarios (SSP3–7.0 and SSP5–8.5). Aerosol pH also plays a critical role in the IEPOX SOA formation rate, requiring accurate calculation of aerosol pH in chemistry models. On the other hand, isoprene SOA calculated with the VBS scheme predicts a nearly constant SOA yield from isoprene emissions across all SSP scenarios; as a result, it mostly follows isoprene emissions regardless of region and scenario. This is because the VBS scheme does not consider heterogeneous chemistry; in other words, there is no dependency on aerosol properties. The discrepancy between the explicit mechanism and VBS parameterization in this study is likely to occur for other SOA components as well, which may also have dependencies that cannot be captured by VBS parameterizations. This study highlights the need for more explicit chemistry or for parameterizations that capture the dependence on key physicochemical drivers when predicting SOA concentrations for climate studies.

Download Full-text

Future changes in isoprene-epoxydiol-derived secondary organic aerosol (IEPOX-SOA) under the shared socioeconomic pathways: the importance of explicit chemistry

10.5194/acp-2020-543 ◽

2020 ◽

Author(s):

Duseong S. Jo ◽

Alma Hodzic ◽

Louisa K. Emmons ◽

Simone Tilmes ◽

Rebecca H. Schwantes ◽

...

Keyword(s):

Secondary Organic Aerosol ◽

Fine Particulate Matter ◽

Formation Rate ◽

Critical Role ◽

Organic Aerosol ◽

Climatic Conditions ◽

Basis Set ◽

Chemical Mechanism ◽

Isoprene Emission ◽

Chemistry Modeling

Abstract. Secondary organic aerosol (SOA) is a dominant contributor of fine particulate matter in the atmosphere, but the complexity of SOA formation chemistry hinders the accurate representation of SOA in models. Volatility-based SOA parameterizations have been adopted in many recent chemistry modeling studies and have shown a reasonable performance compared to observations. However, assumptions made in these empirical parameterizations can lead to substantial errors when applied to future climatic conditions as they do not include the mechanistic understanding of processes but are rather fitted to laboratory studies of SOA formation. This is particularly the case for SOA derived from isoprene epoxydiols (IEPOX-SOA), for which we have a higher level of understanding of the fundamental processes than is currently parameterized in most models. We predict future SOA concentrations using an explicit mechanism, and compare the predictions with the empirical parameterization based on the volatility basis set (VBS) approach. We then use the Community Earth System Model 2 (CESM2.1.0) with detailed isoprene chemistry and reactive uptake processes for the middle and end of the 21st century under four Shared Socioeconomic Pathways (SSPs): SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5. With the explicit chemical mechanism, we find that IEPOX-SOA is predicted to increase on average under all future SSP scenarios, however with some variability in the results depending on regions and the scenario chosen. Isoprene emission is the main driver of IEPOX-SOA changes in the future climate, but IEPOX-SOA yield from isoprene emission also changes by up to 50 % depending on the SSP scenario, in particular due to different sulfur emissions. We conduct sensitivity simulations with and without CO2 inhibition of isoprene emissions that is highly uncertain, which results in a factor of two differences in the predicted IEPOX-SOA global burden, especially for the high-CO2 scenarios (SSP3-7.0 and SSP5-8.5). Aerosol pH also plays a critical role in the IEPOX-SOA formation rate, requiring accurate calculation of aerosol pH in chemistry models. On the other hand, isoprene SOA calculated with the VBS scheme predicts nearly constant SOA yield from isoprene emission across all SSP scenarios, as a result, it mostly follows isoprene emissions regardless of region and scenario. This is because the VBS scheme does not consider heterogeneous chemistry, in other words, there is no dependency on aerosol properties. The discrepancy between the explicit mechanism and VBS parameterization in this study is likely to occur for other SOA components as well, which may also have dependencies that cannot be captured by VBS parameterizations. This study highlights the need for more explicit chemistry, or for parameterizations that capture the dependence on key physico-chemical drivers when predicting SOA concentrations for climate studies.

Download Full-text

Modelling of secondary organic aerosol formation from isoprene photooxidation chamber studies using different approaches

Environmental Chemistry ◽

10.1071/en13029 ◽

2013 ◽

Vol 10 (3) ◽

pp. 194 ◽

Cited By ~ 6

Author(s):

Haofei Zhang ◽

Harshal M. Parikh ◽

Jyoti Bapat ◽

Ying-Hsuan Lin ◽

Jason D. Surratt ◽

...

Keyword(s):

Kinetic Model ◽

Gas Phase ◽

Secondary Organic Aerosol ◽

Organic Aerosol ◽

Basis Set ◽

Chemical Mechanism ◽

Formation Mechanisms ◽

Aerosol Formation ◽

Earth’S Atmosphere ◽

Earth's Atmosphere

Environmental context Fine particulate matter (PM2.5) in the Earth’s atmosphere plays an important role in climate change and human health, in which secondary organic aerosol (SOA) that forms from the photooxidation of volatile organic compounds (VOCs) has a significant contribution. SOA derived from isoprene, the most abundant non-methane VOC emitted into the Earth’s atmosphere, has been widely studied to interpret its formation mechanisms. However, the ability to predict isoprene SOA using current models remains difficult due to the lack of understanding of isoprene chemistry. Abstract Secondary organic aerosol (SOA) formation from the photooxidation of isoprene was simulated against smog chamber experiments with varied concentrations of isoprene, nitrogen oxides (NOx=NO + NO2) and ammonium sulfate seed aerosols. A semi-condensed gas-phase isoprene chemical mechanism (ISO-UNC) was coupled with different aerosol-phase modelling frameworks to simulate SOA formation, including: (1) the Odum two-product approach, (2) the 1-D volatility basis-set (VBS) approach and (3) a new condensed kinetic model based upon the gas-particle partitioning theory and reactive uptake processes. The first two approaches are based upon empirical parameterisations from previous studies. The kinetic model uses a gas-phase mechanism to explicitly predict the major intermediate precursors, namely the isoprene-derived epoxides, and hence simulate SOA formation. In general, they all tend to significantly over predict SOA formation when semivolatile concentrations are higher because more semivolatiles are forced to produce SOA in the models to maintain gas-particle equilibrium; yet the data indicate otherwise. Consequently, modified dynamic parameterised models, assuming non-equilibrium partitioning, were incorporated and could improve the model performance. In addition, the condensed kinetic model was expanded by including an uptake limitation representation so that reactive uptake processes slow down or even stop; this assumes reactive uptake reactions saturate seed aerosols. The results from this study suggest that isoprene SOA formation by reactive uptake of gas-phase precursors is likely limited by certain particle-phase features, and at high gas-phase epoxide levels, gas-particle equilibrium is not obtained. The real cause of the limitation needs further investigation; however, the modified kinetic model in this study could tentatively be incorporated in large-scale SOA models given its predictive ability.

Download Full-text

Limited effect of anthropogenic nitrogen oxides on Secondary Organic Aerosol formation

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-23231-2015 ◽

2015 ◽

Vol 15 (16) ◽

pp. 23231-23277

Author(s):

Y. Zheng ◽

N. Unger ◽

A. Hodzic ◽

L. Emmons ◽

C. Knote ◽

...

Keyword(s):

Nitrogen Oxides ◽

Secondary Organic Aerosol ◽

Critical Role ◽

Organic Aerosol ◽

Atmospheric Model ◽

Basis Set ◽

Aerosol Formation ◽

Aerosol Mass ◽

Anthropogenic Nitrogen ◽

Southeast Us

Abstract. Globally, secondary organic aerosol (SOA) is mostly formed from emissions of biogenic volatile organic compounds (VOCs) by vegetation, but can be modified by human activities as demonstrated in recent research. Specifically, nitrogen oxides (NOx = NO + NO2) have been shown to play a critical role in the chemical formation of low volatility compounds. We have updated the SOA scheme in the global NCAR Community Atmospheric Model version 4 with chemistry (CAM4-chem) by implementing a 4-product Volatility Basis Set (VBS) scheme, including NOx-dependent SOA yields and aging parameterizations. The predicted organic aerosol amounts capture both the magnitude and distribution of US surface annual mean measurements from the Interagency Monitoring of Protected Visual Environments (IMPROVE) network by 50 %, and the simulated vertical profiles are within a factor of two compared to Aerosol Mass Spectrometer (AMS) measurements from 13 aircraft-based field campaigns across different region and seasons. We then perform sensitivity experiments to examine how the SOA loading responds to a 50 % reduction in anthropogenic nitric oxide (NO) emissions in different regions. We find limited SOA reductions of 0.9 to 5.6, 6.4 to 12.0 and 0.9 to 2.8 % for global, the southeast US and the Amazon NOx perturbations, respectively. The fact that SOA formation is almost unaffected by changes in NOx can be largely attributed to buffering in chemical pathways (low- and high-NOx pathways, O3 versus NO3-initiated oxidation) and to offsetting tendencies in the biogenic versus anthropogenic SOA responses.

Download Full-text

Limited effect of anthropogenic nitrogen oxides on secondary organic aerosol formation

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-13487-2015 ◽

2015 ◽

Vol 15 (23) ◽

pp. 13487-13506 ◽

Cited By ~ 12

Author(s):

Y. Zheng ◽

N. Unger ◽

A. Hodzic ◽

L. Emmons ◽

C. Knote ◽

...

Keyword(s):

Nitrogen Oxides ◽

Secondary Organic Aerosol ◽

Critical Role ◽

Organic Aerosol ◽

Atmospheric Model ◽

Basis Set ◽

Aerosol Formation ◽

Aerosol Mass ◽

Anthropogenic Nitrogen ◽

Southeast Us

Abstract. Globally, secondary organic aerosol (SOA) is mostly formed from emissions of biogenic volatile organic compounds (VOCs) by vegetation, but it can be modified by human activities as demonstrated in recent research. Specifically, nitrogen oxides (NOx = NO + NO2) have been shown to play a critical role in the chemical formation of low volatility compounds. We have updated the SOA scheme in the global NCAR (National Center for Atmospheric Research) Community Atmospheric Model version 4 with chemistry (CAM4-chem) by implementing a 4-product volatility basis set (VBS) scheme, including NOx-dependent SOA yields and aging parameterizations. Small differences are found for the no-aging VBS and 2-product schemes; large increases in SOA production and the SOA-to-OA ratio are found for the aging scheme. The predicted organic aerosol amounts capture both the magnitude and distribution of US surface annual mean measurements from the Interagency Monitoring of Protected Visual Environments (IMPROVE) network by 50 %, and the simulated vertical profiles are within a factor of 2 compared to aerosol mass spectrometer (AMS) measurements from 13 aircraft-based field campaigns across different regions and seasons. We then perform sensitivity experiments to examine how the SOA loading responds to a 50 % reduction in anthropogenic nitric oxide (NO) emissions in different regions. We find limited SOA reductions of 0.9–5.6, 6.4–12.0 and 0.9–2.8 % for global, southeast US and Amazon NOx perturbations, respectively. The fact that SOA formation is almost unaffected by changes in NOx can be largely attributed to a limited shift in chemical regime, to buffering in chemical pathways (low- and high-NOx pathways, O3 versus NO3-initiated oxidation) and to offsetting tendencies in the biogenic versus anthropogenic SOA responses.

Download Full-text

Exploration of oxidative chemistry and secondary organic aerosol formation in the Amazon during the wet season: explicit modeling of the Manaus urban plume with GECKO-A

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-5995-2020 ◽

2020 ◽

Vol 20 (10) ◽

pp. 5995-6014 ◽

Cited By ~ 1

Author(s):

Camille Mouchel-Vallon ◽

Julia Lee-Taylor ◽

Alma Hodzic ◽

Paulo Artaxo ◽

Bernard Aumont ◽

...

Keyword(s):

Secondary Organic Aerosol ◽

Background Level ◽

Organic Aerosol ◽

Oxidation Products ◽

Box Model ◽

Basis Set ◽

Aerosol Formation ◽

Wet Season ◽

Urban Plume ◽

The Impact

Abstract. The GoAmazon 2014/5 field campaign took place in Manaus, Brazil, and allowed the investigation of the interaction between background-level biogenic air masses and anthropogenic plumes. We present in this work a box model built to simulate the impact of urban chemistry on biogenic secondary organic aerosol (SOA) formation and composition. An organic chemistry mechanism is generated with the Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere (GECKO-A) to simulate the explicit oxidation of biogenic and anthropogenic compounds. A parameterization is also included to account for the reactive uptake of isoprene oxidation products on aqueous particles. The biogenic emissions estimated from existing emission inventories had to be reduced to match measurements. The model is able to reproduce ozone and NOx for clean and polluted situations. The explicit model is able to reproduce background case SOA mass concentrations but does not capture the enhancement observed in the urban plume. The oxidation of biogenic compounds is the major contributor to SOA mass. A volatility basis set (VBS) parameterization applied to the same cases obtains better results than GECKO-A for predicting SOA mass in the box model. The explicit mechanism may be missing SOA-formation processes related to the oxidation of monoterpenes that could be implicitly accounted for in the VBS parameterization.

Download Full-text

Modeling organic aerosols in a megacity: comparison of simple and complex representations of the volatility basis set approach

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-10-30205-2010 ◽

2010 ◽

Vol 10 (12) ◽

pp. 30205-30277 ◽

Cited By ~ 7

Author(s):

M. Shrivastava ◽

J. Fast ◽

R. Easter ◽

W. I. Gustafson ◽

R. A. Zaveri ◽

...

Keyword(s):

Gas Phase ◽

Secondary Organic Aerosol ◽

Computational Cost ◽

Organic Aerosols ◽

Field Measurements ◽

Organic Aerosol ◽

Basis Set ◽

Aerosol Formation ◽

Secondary Organic Aerosol Formation ◽

The City

Abstract. The Weather Research and Forecasting model coupled with chemistry (WRF-Chem) is modified to include a volatility basis set (VBS) treatment of secondary organic aerosol formation. The VBS approach, coupled with SAPRC-99 gas-phase chemistry mechanism, is used to model gas-particle partitioning and multiple generations of gas-phase oxidation of organic vapors. In addition to the detailed 9-species VBS, a simplified mechanism using 2 volatility species (2-species VBS) is developed and tested for similarity to the 9-species VBS in terms of both mass and oxygen-to-carbon ratios of organic aerosols in the atmosphere. WRF-Chem results are evaluated against field measurements of organic aerosols collected during the MILAGRO 2006 campaign in the vicinity of Mexico City. The simplified 2-species mechanism reduces the computational cost by a factor of 2 as compared to 9-species VBS. Both ground site and aircraft measurements suggest that the 9-species and 2-species VBS predictions of total organic aerosol mass as well as individual organic aerosol components including primary, secondary, and biomass burning are comparable in magnitude. In addition, oxygen-to-carbon ratio predictions from both approaches agree within 25%, providing evidence that the 2-species VBS is well suited to represent the complex evolution of organic aerosols. Model sensitivity to amount of anthropogenic semi-volatile and intermediate volatility (S/IVOC) precursor emissions is also examined by doubling the default emissions. Both the emission cases significantly under-predict primary organic aerosols in the city center and along aircraft flight transects. Secondary organic aerosols are predicted reasonably well along flight tracks surrounding the city, but are consistently over-predicted downwind of the city. Also, oxygen-to-carbon ratio predictions are significantly improved compared to prior studies by adding 15% oxygen mass per generation of oxidation; however, all modeling cases still under-predict these ratios downwind as compared to measurements, suggesting a need to further improve chemistry parameterizations of secondary organic aerosol formation.

Download Full-text

Secondary organic aerosol formation from smoldering and flaming combustion of biomass: a box model parametrization based on volatility basis set

10.5194/acp-2018-1308 ◽

2019 ◽

Cited By ~ 2

Author(s):

Giulia Stefenelli ◽

Jianhui Jiang ◽

Amelie Bertrand ◽

Emily A. Bruns ◽

Simone M. Pieber ◽

...

Keyword(s):

Mass Spectrometer ◽

Secondary Organic Aerosol ◽

Time Of Flight ◽

Organic Aerosol ◽

Box Model ◽

Basis Set ◽

Model Parameters ◽

Oh Radicals ◽

Smog Chamber ◽

Aerosol Formation

Abstract. Box model simulations based on the volatility basis set (VBS) approach were used to assess secondary organic aerosol (SOA) precursors and volatility distributions from residential wood combustion. Emissions were sampled from three different residential stoves at different combustion conditions (flaming vs. smoldering-dominated), aging temperatures (−10 °C, 2 °C and 15 °C), and emission loads, then exposed to hydroxyl (OH) radicals in a smog chamber. Primary emissions of SOA precursor compounds, organic aerosol and their evolution during aging in the smog chamber were monitored by a comprehensive suite of gas and particle instrumentation, including a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) and a high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). SOA precursors were classified according to their chemical composition and the identification of the nature of the precursors revealed useful to better constrain model parameters, in particular SOA production rates and molecular characteristics of the condensable gases formed. The general aim of the model was the determination of the parameters describing the volatility distributions of the oxidation products from the different chemical classes considered and their temperature dependence. Novel parameterization methods based on a genetic algorithm (GA) approach allowed estimation of precursor class contributions to SOA and evaluation of the effect of emission variability on SOA yield predictions. Significant differences were observed in the gas-phase composition between smoldering and flaming emissions. Smoldering phase emissions were dominated by oxidized VOCs with less than six carbon atoms family (OVOCc

Download Full-text

Simulating regional scale secondary organic aerosol formation during the TORCH 2003 campaign in the southern UK

Atmospheric Chemistry and Physics ◽

10.5194/acp-6-403-2006 ◽

2006 ◽

Vol 6 (2) ◽

pp. 403-418 ◽

Cited By ~ 131

Author(s):

D. Johnson ◽

S. R. Utembe ◽

M. E. Jenkin ◽

R. G. Derwent ◽

G. D. Hayman ◽

...

Keyword(s):

Secondary Organic Aerosol ◽

Regional Scale ◽

Organic Aerosol ◽

Chemical Mechanism ◽

Background Concentration ◽

Aerosol Formation ◽

Organic Species ◽

Voc Oxidation ◽

Partitioning Coefficients

Abstract. A photochemical trajectory model has been used to simulate the chemical evolution of air masses arriving at the TORCH field campaign site in the southern UK during late July and August 2003, a period which included a widespread and prolonged photochemical pollution episode. The model incorporates speciated emissions of 124 non-methane anthropogenic VOC and three representative biogenic VOC, coupled with a comprehensive description of the chemistry of their degradation. A representation of the gas/aerosol absorptive partitioning of ca. 2000 oxygenated organic species generated in the Master Chemical Mechanism (MCM v3.1) has been implemented, allowing simulation of the contribution to organic aerosol (OA) made by semi- and non-volatile products of VOC oxidation; emissions of primary organic aerosol (POA) and elemental carbon (EC) are also represented. Simulations of total OA mass concentrations in nine case study events (optimised by comparison with observed hourly-mean mass loadings derived from aerosol mass spectrometry measurements) imply that the OA can be ascribed to three general sources: (i) POA emissions; (ii) a "ubiquitous" background concentration of 0.7 µg m-3; and (iii) gas-to-aerosol transfer of lower volatility products of VOC oxidation generated by the regional scale processing of emitted VOC, but with all partitioning coefficients increased by a species-independent factor of 500. The requirement to scale the partitioning coefficients, and the implied background concentration, are both indicative of the occurrence of chemical processes within the aerosol which allow the oxidised organic species to react by association and/or accretion reactions which generate even lower volatility products, leading to a persistent, non-volatile secondary organic aerosol (SOA). The contribution of secondary organic material to the simulated OA results in significant elevations in the simulated ratio of organic carbon (OC) to EC, compared with the ratio of 1.1 assigned to the emitted components. For the selected case study events, [OC]/[EC] is calculated to lie in the range 2.7-9.8, values which are comparable with the high end of the range reported in the literature.

Download Full-text

Mapping gas-phase organic reactivity and concomitant secondary organic aerosol formation: chemometric dimension reduction techniques for the deconvolution of complex atmospheric data sets

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-8077-2015 ◽

2015 ◽

Vol 15 (14) ◽

pp. 8077-8100 ◽

Cited By ~ 7

Author(s):

K. P. Wyche ◽

P. S. Monks ◽

K. L. Smallbone ◽

J. F. Hamilton ◽

M. R. Alfarra ◽

...

Keyword(s):

Phase Composition ◽

Dimension Reduction ◽

Gas Phase ◽

Secondary Organic Aerosol ◽

Ambient Air ◽

Organic Aerosol ◽

Chemical Mechanism ◽

Particle Phase ◽

Aerosol Formation ◽

Holistic View

Abstract. Highly non-linear dynamical systems, such as those found in atmospheric chemistry, necessitate hierarchical approaches to both experiment and modelling in order to ultimately identify and achieve fundamental process-understanding in the full open system. Atmospheric simulation chambers comprise an intermediate in complexity, between a classical laboratory experiment and the full, ambient system. As such, they can generate large volumes of difficult-to-interpret data. Here we describe and implement a chemometric dimension reduction methodology for the deconvolution and interpretation of complex gas- and particle-phase composition spectra. The methodology comprises principal component analysis (PCA), hierarchical cluster analysis (HCA) and positive least-squares discriminant analysis (PLS-DA). These methods are, for the first time, applied to simultaneous gas- and particle-phase composition data obtained from a comprehensive series of environmental simulation chamber experiments focused on biogenic volatile organic compound (BVOC) photooxidation and associated secondary organic aerosol (SOA) formation. We primarily investigated the biogenic SOA precursors isoprene, α-pinene, limonene, myrcene, linalool and β-caryophyllene. The chemometric analysis is used to classify the oxidation systems and resultant SOA according to the controlling chemistry and the products formed. Results show that "model" biogenic oxidative systems can be successfully separated and classified according to their oxidation products. Furthermore, a holistic view of results obtained across both the gas- and particle-phases shows the different SOA formation chemistry, initiating in the gas-phase, proceeding to govern the differences between the various BVOC SOA compositions. The results obtained are used to describe the particle composition in the context of the oxidised gas-phase matrix. An extension of the technique, which incorporates into the statistical models data from anthropogenic (i.e. toluene) oxidation and "more realistic" plant mesocosm systems, demonstrates that such an ensemble of chemometric mapping has the potential to be used for the classification of more complex spectra of unknown origin. More specifically, the addition of mesocosm data from fig and birch tree experiments shows that isoprene and monoterpene emitting sources, respectively, can be mapped onto the statistical model structure and their positional vectors can provide insight into their biological sources and controlling oxidative chemistry. The potential to extend the methodology to the analysis of ambient air is discussed using results obtained from a zero-dimensional box model incorporating mechanistic data obtained from the Master Chemical Mechanism (MCMv3.2). Such an extension to analysing ambient air would prove a powerful asset in assisting with the identification of SOA sources and the elucidation of the underlying chemical mechanisms involved.

Download Full-text

Improving the representation of secondary organic aerosol (SOA) in the MOZART-4 global chemical transport model

Geoscientific Model Development Discussions ◽

10.5194/gmdd-5-4187-2012 ◽

2012 ◽

Vol 5 (4) ◽

pp. 4187-4232 ◽

Cited By ~ 1

Author(s):

A. Mahmud ◽

K. C. Barsanti

Keyword(s):

South America ◽

Secondary Organic Aerosol ◽

Transport Model ◽

Organic Aerosol ◽

Basis Set ◽

Base Case ◽

Chemical Transport Model ◽

Annual Average ◽

Modeling Studies ◽

The Usa

Abstract. The secondary organic aerosol (SOA) module in the Model for Ozone and Related chemical Tracers, version 4 (MOZART-4) has been updated by replacing existing two-product (2p) parameters with those obtained from two-product volatility basis set (2p-VBS) fits, and by treating SOA formation from the following volatile organic compounds (VOCs): isoprene, propene and lumped alkenes. Strong seasonal and spatial variations in global SOA distributions were demonstrated, with significant differences in the predicted concentrations between the base-case and updated model versions. The base-case MOZART-4 predicted annual average SOA of 0.36 ± 0.50 μg m−3 in South America, 0.31 ± 0.38 μg m−3 in Indonesia, 0.09 ± 0.05 μg m−3 in the USA, and 0.12 ± 0.07 μg m−3 in Europe. Concentrations from the updated versions of the model showed a~marked increase in annual average SOA. Using the updated set of parameters alone (MZ4-v1) increased annual average SOA by ~8%, ~16%, ~56%, and ~108% from the base-case in South America, Indonesia, USA, and Europe, respectively. Treatment of additional parent VOCs (MZ4-v2) resulted in an even more dramatic increase of ~178–406% in annual average SOA for these regions over the base-case. The increases in predicted SOA concentrations further resulted in increases in corresponding SOA contributions to annual average total aerosol optical depth (AOD) by <1% for MZ4-v1 and ~1–6% for MZ4-v2. Estimated global SOA production was ~6.6 Tg yr−1 and ~19.1 Tg yr−1 with corresponding burdens of ~0.24 Tg and ~0.59 Tg using MZ4-v1 and MZ4-v2, respectively. The SOA budgets predicted in the current study fall well within reported ranges for similar modeling studies, 6.7 to 96 Tg yr−1, but are lower than recently reported observationally-constrained values, 50 to 380 Tg yr−1. With MZ4-v2, simulated SOA concentrations at the surface were also in reasonable agreement with comparable modeling studies and observations. Concentrations of estimated organic aerosol (OA) at the surface, however, showed under-prediction in Europe and over-prediction in the Amazonian regions and Malaysian Borneo during certain months of the year. Overall, the updated version of MOZART-4, MZ4-v2, showed consistently better skill in predicting SOA and OA levels and spatial distributions as compared with unmodified MOZART-4. The MZ4-v2 updates may be particularly important when MOZART-4 output is used to generate boundary conditions for regional air quality simulations that require more accurate representation of SOA concentrations and distributions.

Download Full-text