Advances in Modelling Secondary Organic Aerosol - from Particle Formation to Climate Impact
Abstract
The ability of large-scale atmospheric models to simulate the dynamics of volatile organic compounds (VOCs) and the formation of secondary organic aerosol (SOA) is challenged by uncertainties in the associated particle-scale physical and chemical processes.
We implement a new SOA formation scheme in a global aerosol model to investigate the role of atmospheric VOCs on the simulated aerosol size distribution. Our scheme includes three categories of highly oxygenated molecules (HOMs) derived from the oxidation of biogenic and anthropogenic precursor VOCs: extremely low volatility organic compounds (ELVOCs) that nucleate, low volatility organic compounds (LVOCs) that grow nucleated clusters by kinetic condensation and semi-volatile organic compounds (SVOCs) that grow larger particles in the model by thermodynamic partitioning. The behaviour of ELVOCs in the model is based on the results of the CERN CLOUD Experiment. We further explore a large uncertainty range for each of the VOC categories, comparing them with observations of multiple model outputs. Our study strongly emphasises the role of low-volatility HOMs in modulating the aerosol size distribution. Unless large-scale models include a robust representation of LVOCs growing freshly nucleated particles, the impact of new sophisticated nucleation parameterisations on large-scale aerosol effects on clouds and radiation will be hugely undermined. LVOCs have the strongest impact on the number concentration of climate-relevant sized particles. Our study also reveals a structural deficiency in the model, which we strongly suggest is due to the missing contributions of anthropogenic VOCs to particle nucleation and cluster growth. Further we demonstrate the challenges involved in simulating both number and mass concentrations correctly in a global aerosol model. VOCs of varying volatilites have competing as well as compensating effects on modelled aerosol properties. Our study identifies the plausible parameter ranges of key VOCs that have a significant impact on determining the climatic impacts of atmospheric aerosols. The ability of large-scale atmospheric models to simulate the dynamics of volatile organic compounds (VOCs) and the formation of secondary organic aerosol (SOA) is challenged by uncertainties in the associated particle-scale physical and chemical processes. We implement a new SOA formation scheme in a global aerosol model to investigate the role of atmospheric VOCs on the simulated aerosol size distribution. Our scheme includes three categories of highly oxygenated molecules (HOMs) derived from the oxidation of biogenic and anthropogenic precursor VOCs: extremely low volatility organic compounds (ELVOCs) that nucleate, low volatility organic compounds (LVOCs) that grow nucleated clusters by kinetic condensation and semi-volatile organic compounds (SVOCs) that grow larger particles in the model by thermodynamic partitioning. The representation of ELVOCs in the model is based on the results of the CERN CLOUD Experiment. We further explore a large uncertainty range for each of the VOC categories, comparing them with observations of multiple model outputs. Our study strongly emphasises the role of low-volatility HOMs in modulating the aerosol size distribution. Unless large-scale models include a robust representation of LVOCs growing freshly nucleated particles, the impact of new sophisticated nucleation parameterisations on large-scale aerosol effects on clouds and radiation will be hugely undermined. LVOCs have the strongest impact on the number concentration of climate-relevant sized particles. Our study also reveals a structural deficiency in the model, which we strongly suggest is due to the missing contributions of anthropogenic VOCs to particle nucleation and cluster growth. Further we demonstrate the challenges involved in simulating both number and mass concentrations correctly in a global aerosol model. VOCs of varying volatilites have competing as well as compensating effects on modelled aerosol properties. Based on those competing and compensating effects, our study identifies plausible parameter ranges of key SOA-producing VOCs which significantly affect model estimates of climatic impacts of atmospheric aerosols.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.A43K3216S
- Keywords:
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- 0305 Aerosols and particles;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0320 Cloud physics and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0368 Troposphere: constituent transport and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 3311 Clouds and aerosols;
- ATMOSPHERIC PROCESSES