Definition of Sulphate Aerosol
However, the UNFCCC found that sulphate aerosols only remain in the atmosphere for a short time compared to well-mixed greenhouse gases, and therefore their cooling is localized and temporary. Other side effects of sulphate aerosols in the environment include poor air quality. [1] There are a number of different projections for sulphate aerosol emissions over the next century based on assumptions about economic growth rate, population growth and technological development. Figure two below shows an aggregation of all anthropogenic sulphate emission models used in the latest IPCC report. Specific scenarios vary widely, but the median value of all models is 35 million tonnes of sulphate aerosol emissions by 2100, about half of current emissions. Aerosol particles attract a certain amount of moisture, which increases with relative humidity. Clouds and fog form when adiabatic or radiant cooling of the air increases relative humidity (r.h.) beyond the point of moisture saturation. The formation of water droplets requires aerosol particles, which can act as condensation nuclei. In the field of supersaturation, at >100%, the condensation of water on particles comes up against a size-dependent barrier that can only be overcome by large particles (>0.1 μm) for accessible degrees of supersaturation (<0.4%). Once these particles are activated, they can continue to grow to form cloud droplets, while smaller particles remain present as interstitial aerosols.
When the cloud droplets evaporate again, the particles are reassembled. Most clouds dissolve, allowing aerosol particles to pass through several cycles of cloud condensation before finally being incorporated into a rain cloud that removes them from the troposphere. In mid-latitudes, wet precipitation provides an efficient deposition mechanism that results in an aerosol lifetime of 5 to 7 days for particles between 0.1 and 10 μm in size. Influence of sulphate aerosols on the physical and optical properties of clouds The importance of sulphur in the Earth`s atmosphere and environment is well established. Aerosol sulfate is known to alter atmospheric radiation processes due to its role in increasing terrestrial albedo and as a cloud condensation core, and is a component of the sulfur cycle and environmental acidification. While these important roles are recognized, there are still significant gaps in understanding the role of aerosols in these processes. An important role of isotopic analysis is the identification of sources, transport and mechanistic definition of chemical transformation processes in situ. Sulphate and nitrate aerosols are known ways to increase the incidence of cardiovascular disease, and defining surface properties may be important for such studies, but is notoriously difficult to measure. Nitrate is a means of altering terrestrial biodiversity when sufficient amounts are added to soils and rivers.
The distribution of nitrate sources is difficult due to the large number of vectors; Therefore, new techniques to support source recognition are welcome. Single isotope ratio measurements have always been of limited benefit in solving these problems due to the limited specificity of single isotope ratio measurements such as δ15N, δ34S or δ18O. Figure 1 shows the momentary and effective annual average radiative forcing when SO2 emissions from the fuel are reduced to zero with the current CO2 concentration simulated by MIROC-SPRINTARS. The current radiative forcing has been attributed to aerosol-radiation interactions and represents approximately a change in sulphate aerosol concentration. It was largest in East and South Asia, followed by concentrations in Southeast Asia, North and Central America, and Europe. Significant effective radiative forcing has been extended to regions of oceanic runoff of sulphate aerosols, particularly over tropical Asia and storm paths in the North Pacific and North Atlantic due to aerosol cloud interactions where cloud water levels are high. Sulphate aerosols produced by combustion are mainly found in the size range of 0.1 to 2 μm, where atmospheric dry deposition processes are slow and inefficient; Dry deposition is therefore not considered an important removal process in most regions. However, recent field measurements suggest that dry deposition may be greater than the theory suggests. Wet deposition is the most important removal process for sulphates, with nucleation contributing about 65% to wet deposited sulfur and DISSOLUTION and oxidation of SO2 contributing 20% to 20%, in areas far from sources. As soon as the sulfate ion is bound to the elements of the cloudy water, it is subjected to the stormy behavior of the associated water.
In the past, sulphate deposition in haze, dew and frost was neglected when measuring wet deposition. This can lead to a significant underestimation of total sulphate deposition, especially since ion concentrations in these forms of deposition are relatively high. Much of the annual sulphate deposition can be caused by fog trapping and cloud droplets, although deposition rates are high under wet conditions. Precipitation is released to coal-fired power sources, with primary sulphates and dissolved SO2 mainly removed relatively close to the plants. In addition to trace gases, the troposphere contains finely dispersed particles with a size of about 0.002 to 50 μm, the atmospheric aerosol. The highest concentration of aerosol particles occurs in urban air (>1011 m−3 particles), low values are found in seafloor air (3 × 108 m−3 particles) and even lower values above the poles. The mass concentration also decreases from ∼100 μg m−3 in city air to 10 μg m−3 in sea air. The mass of a particle increases with its volume, so the mass concentration of the aerosol is determined by the number of larger particles in the assembly in the size range of 0.1 to 50 μm. Both concentrations decrease as one moves from urban to remote areas, but mass concentration and numerical density are not linearly correlated as the average particle size changes and becomes larger in the distant troposphere. The aerosol concentration also decreases with altitude.
In the free troposphere, the decline is approximately proportional to the density of the air, in the boundary layer, the decline is more pronounced. This study used a general circulation model in conjunction with an aerosol process model, MIROC-SPRINTARS8,9,10, which calculates the overall spatio-temporal distributions of the mass mixing ratios of each aerosol component as prognostic variables. The model takes into account changes in the meteorological range due to radiation and cloud precipitation processes in the form of aerosol or aerosol-cloud interactions using the predicted aerosol mass mixing ratio. The simulated results of MIROC-SPRINTARS have been confirmed as appropriate by various methods, including comparisons between models and with observations, e.g. aerosol comparisons between observations and models (AeroCom) 11,12,13. Sensitivity experiments using disturbed SO2 emissions from a realistic range of fuel sources (factors of 0.0, 0.1, 0.3, 0.5, 0.8, 1.5 and 2.0 compared to current emissions) were lower than current emissions (369 ppm recorded in 2000) and doubled (738 ppm, close to SSP3-7.0 scenario for 2080) compared to today`s (369 ppm, recorded in 200) and doubled (738 ppm, near the SSP3 scenario 7.0 for 2080). The SSP3-7.0 scenario is published under the title Shared Socioeconomic Pathways (SSP)14.15 Future Scenario, which will be used in the IPCC`s 6th Assessment Report (AR6) in 2021; The scenario will be used as a standard future scenario in the Aerosol Chemistry Model Intercomparison Project (AerChemMIP)16, which will contribute to the IPCC AR6. In SSP3-7.0, greenhouse gas emissions are close to the total Nationally Determined Contributions that each country has submitted to the 2030 United Nations Framework Convention on Climate Change (UNFCCC) and are expected to continue to grow at the same rate until the end of the twenty-first century. The experimental model and parameters are described in detail in the “Methods” section. The single-model approach does not take into account differences in physical representation, allowing for consistent sensitivity experiments.
Finally, a number of gas-phase chemical reactions, such as oxidation of selected organic compounds, produce non-volatile condensable products associated with aerosol particles. Much of the aerosol consists of ammonium sulfate, which is formed by the oxidation of sulfur dioxide to sulfuric acid and its reaction with ammonia. The overall rate of aerosol sulphate production from biogenic sulphur gases is 60-110 Tg year−1, volcanic sulphur dioxide sulphate adds about 25 Tg year−1, while sulphate from the oxidation of anthropogenic sulphur dioxide contributes to 60–180 Tg an−1. The production of nitrates from the oxidation of nitrogen dioxide is 40 to 100 Tg per year-1, with roughly equal contributions from anthropogenic and natural sources. The rate of production of non-volatile organic substances associated with aerosol is highly uncertain. Estimates range from 40 to 200 Tg in year 1. Among the most significant changes in climate change modelling between the 2001 IPCC Third Assessment Report (TAR) and the 2007 Fourth Assessment Report (AR4) was a revision of the expected evolution of man-made sulphate aerosol emissions. In the previous report, scientists assumed that aerosols would largely increase relative to economic growth. The authors of the 2007 report acknowledged that aerosol emissions, which have direct and immediate negative effects on people`s health around their emissions, are likely to be reduced as countries like China and India become more prosperous. This reduction in emissions would reflect a process similar to that which took place in Europe and the United States. Takemura, T., Nozawa, T., Emori, S., Nakajima, T. Y.
& Nakajima, T. Simulation of the climate response to the direct and indirect effects of aerosols using the aerosol transport radiation model.