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Annual mean surface concentrations of PM2.5 for (i) SO42-, (ii) NH4+ and (iii) NO3- as simulated by EMAC using ISORROPIA-lite (shaded contours) versus observations of the same species from the IMPROVE, EMEP and EANET networks (colored circles).
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This study explores the differences in performance and results by various versions of the ISORROPIA thermodynamic module implemented within the ECHAM/MESSy Atmospheric Chemistry (EMAC) model. Three different versions of the module were used, ISORROPIA II v1, ISORROPIA II v2.3, and ISORROPIA-lite. First, ISORROPIA II v2.3 replaced ISORROPIA II v1 in...
Citations
... Overall, the OOA contribution range from 19% 339 (urban minimum) to 99% (rural maximum). The extreme shares were both found during computational speed of the model by 4% (Milousis et al., 2024). The assumption of 474 thermodynamic equilibrium is a good approximation for fine mode aerosols which can 475 reach equilibrium within the time frame of one model timestep. ...
... EMAC uses the Modular 424 Earth Submodel System (MESSy2)(Jöckel et al., 2010) to link the different sub-models425 with an atmospheric dynamical core, being an updated version of the 5th generation 426 European Centre -Hamburg general circulation model (ECHAM5)(Roeckner et al., 427 2006). The EMAC model has been extensively described and evaluated against 428 observations and satellite measurements and can be applied to a range of spatial 429 resolutionsKarydis et al., 2016; Janssen et al., 2017; Tsimpidi 430 et al., 2018; Pozzer et al., 2022;Milousis et al., 2024). The spectral resolution used in 431 this study is T63L31, corresponding to a horizontal grid resolution of 1.875 o x1.875 o 432 and 31 vertical layers extending to 10 hPa at about 25 km from the surface. ...
... State of the art module for organic aerosol486 The organic aerosol composition and evolution in the atmosphere is calculated by487 the ORACLE module(Tsimpidi et al., 2024). ORACLE is a computationally efficient 488 version of the ORACLE module(Tsimpidi et al., 2014) which simulates a wide variety 489 of semi-volatile organic products separating them into bins of logarithmically spaced 490 effective saturation concentrations. ...
Atmospheric aerosols significantly impact Earth’s climate and air quality. In addition to their number and mass concentrations, their chemical composition influences their environmental and health effects. This study examines global trends in aerosol composition from 2000 to 2020, using the EMAC atmospheric chemistry-climate model and a variety of observational datasets. These include PM2.5 data from regional networks and 744 PM1 datasets from AMS field campaigns conducted at 169 sites worldwide. Results show that organic aerosol (OA) is the dominant fine aerosol component in all continental regions, particularly in areas with significant biomass burning and biogenic VOC emissions. EMAC effectively reproduces the prevalence of secondary OA but underestimates the aging of OA in some cases, revealing uncertainties in distinguishing fresh and aged SOA. While sulfate is a major aerosol component in filter-based observations, AMS and model results indicate nitrate predominates in Europe and Eastern Asia. Mineral dust also plays a critical role in specific regions, as highlighted by EMAC. The study identifies substantial declines in sulfate, nitrate, and ammonium concentrations in Europe and North America, attributed to emission controls, with varying accuracy in model predictions. In Eastern Asia, sulfate reductions due to SO2 controls are partially captured by the model. OA trends differ between methodologies, with filter data showing slight decreases, while AMS data and model simulations suggest slight increases in PM1 OA across Europe, North America, and Eastern Asia. This research underscores the need for integrating advanced models and diverse datasets to better understand aerosol trends and guide environmental policy.
... Each regime addresses a specific subset of relevant species and equilibrium equations. Efficiency is further improved by retrieving species' activity coefficients from look-up tables (Fountoukis and Nenes, 2007;Milousis et al., 2024). The medium acidity is determined by the concentrations of acidic/basic gaseous species (HNO 3(g) , NH 3(g) , H 2 SO 4(g) ), ...
... Previous studies comparing stable and metastable methodologies with ISORROPIA-II have reported only marginal differences in global nitrate budgets between both modes. These differences noted slightly lower pH values and nitrate formation when using the metastable assumption (Karydis et al., 2016(Karydis et al., , 2021Milousis et al., 2024). ...
Desert dust undergoes complex heterogeneous chemical reactions during atmospheric transport, forming nitrate coatings that impact hygroscopicity, gas species partitioning, optical properties, and aerosol radiative forcing. Contemporary atmospheric chemistry models show significant disparities in aerosol nitrogen species due to varied parameterizations and inaccuracies in representing heterogeneous chemistry and dust alkalinity. This study investigates key processes in nitrate formation over dust and evaluates their representation in models. We incorporate varying levels of dust heterogeneous chemistry complexity into the MONARCH model, assessing sensitivity to key processes. Our analyses focus on the condensation pathways of gas species onto dust (irreversible and reversible), the influence of nitrate representation on species' burdens and lifetimes, size distribution, and the alkalinity role. Using annual global simulations, we compare particulate and gas species surface concentrations against observations and evaluate global budgets and spatial distributions. Findings show significant outcome dependence on methodology, particularly on the reversible or irreversible condensation of gas species on particles, with a wide range of burdens for particulate nitrate (0.66 to 1.93 Tg) and correlations with observations (0.66 to 0.91). Particulate ammonium burdens display less variability (0.19 to 0.31 Tg). Incorporating dust and sea-salt alkalinity yields results more consistent with observations, and assuming reversible gas condensation over dust, along with alkalinity representation, aligns best with observations, while providing consistent gas and particle partitioning. In contrast, irreversible uptake reactions overestimate coarse particulate nitrate formation. Our analysis provides guidelines for integrating nitrate heterogeneous formation on dust in models, paving the road for improved estimates of aerosol radiative effects.
Ammonia (NH3) is an abundant alkaline gas in the atmosphere and a key precursor in the formation of particulate matter. While emissions of other aerosol precursors such as SO2 and NOx have decreased significantly, global NH3 emissions are stable or increasing, and this trend is projected to continue. This study investigates the impact of NH3 emission changes on size-resolved aerosol composition and acidity using the atmospheric chemistry-climate model EMAC. Three NH3 emission schemes are analyzed: two bottom-up inventories and one derived using an updated top-down method. The results reveal that sulphate-nitrate-ammonium aerosols in two fine mode size ranges (0–1 µm and 1–2.5 µm) show the greatest sensitivity to NH3 emission changes. Regional responses vary depending on the local chemical environment of secondary inorganic aerosols. In 'NH3-rich' regions (e.g. East Asia and Europe), the abundance of NH3 partially offsets the effects of reduced NH3 emissions when NOx and SO2 are available, especially for aerosols in the 1–2.5 µm range. This highlights the importance of coordinated control strategies for NH3, NOx and SO2 emissions. Further, we find that NH3 has a buffering effect in densely populated areas, maintaining aerosol acidity at moderate levels and mitigating drastic pH shifts. The study emphasizes that pH changes are closely related to NH3 emission variations, with the highest sensitivity observed in the fine mode size ranges. These results highlight the critical role of NH3 in shaping aerosol acidity and argue for size-specific approaches to managing particulate matter.
In recent years, nitrate aerosols have emerged as a dominant component of atmospheric composition, surpassing sulfate aerosols in both concentration and climatic impact. However, accurately simulating nitrate aerosols remains a significant challenge for global atmospheric models due to the complexity of their formation and regional variability. This study investigates key factors influencing nitrate aerosol formation to improve simulation accuracy in highly polluted regions. Using the advanced EMAC climate and chemistry model, we assess the effects of grid resolution, emission inventories, and thermodynamic, chemical, and aerosol scavenging processes. The ISORROPIA II thermodynamic model is employed to simulate the formation of inorganic aerosols. Model predictions are compared with surface observations of particulate nitrate in PM1 and PM2.5 size fractions, including PM2.5 data from filter-based observational networks and PM1 data from aerosol mass spectrometer field campaigns across Europe, North America, East Asia, and India. Results show that the model overestimates PM2.5 nitrate concentrations, especially in East Asia, with biases up to a factor of three. Increasing grid resolution, adjusting N2O5 hydrolysis uptake coefficient, and utilizing an appropriate emission database (e.g., CMIP6) improve performance. However, these adjustments do not necessarily enhance PM1 predictions, which remain underestimated, especially in urban downwind sites. Seasonal variations and diurnal trends reveal discrepancies in model performance, especially in Europe and urban downwind locations. In Europe, model bias is driven by an unrealistically sharp decrease in nitrate aerosol levels from morning maxima to evening minima. Sensitivity tests show relatively small impact on total tropospheric nitrate burden, with variations within 25 %.
Nitrate (NO3-) aerosol is projected to increase dramatically in the coming decades and may become the dominant inorganic particle species. This is due to the continued strong decrease in SO2 emissions, which is not accompanied by a corresponding decrease in NOx and especially NH3 emissions. Thus, the radiative effect (RE) of NO3- aerosol may become more important than that of SO42- aerosol in the future. The physicochemical interactions of mineral dust particles with gas and aerosol tracers play an important role in influencing the overall RE of dust and non-dust aerosols but can be a major source of uncertainty due to their lack of representation in many global climate models. Therefore, this study investigates how and to what extent dust affects the current global NO3- aerosol radiative effect through both radiation (REari) and cloud interactions (REaci) at the top of the atmosphere (TOA). For this purpose, multi-year simulations nudged towards the observed atmospheric circulation were performed with the global atmospheric chemistry and climate model EMAC, while the thermodynamics of the interactions between inorganic aerosols and mineral dust were simulated with the thermodynamic equilibrium model ISORROPIA-lite. The emission flux of the mineral cations Na+, Ca2+, K+ and Mg2+ is calculated as a fraction of the total aeolian dust emission based on the unique chemical composition of the major deserts worldwide. Our results reveal positive and negative shortwave and longwave radiative effects in different regions of the world via aerosol-radiation interactions and cloud adjustments. Overall, the NO3- aerosol direct effect contributes a global cooling of -0.11 W/m2, driven by coarse-mode particle cooling at short wavelengths. Regarding the indirect effect, it is noteworthy that NO3- aerosol exerts a global mean warming of +0.17 W/m2. While the presence of NO3- aerosol enhances the ability of mineral dust particles to act as cloud condensation nuclei (CCN), it simultaneously inhibits the formation of cloud droplets from the smaller anthropogenic particles. This is due to the coagulation of fine anthropogenic CCN particles with the larger nitrate-coated mineral dust particles, which leads to a reduction in total aerosol number concentration. This mechanism results in an overall reduced cloud albedo effect and is thus attributed as warming.
