No description available.

No description available.

No description available.

No description available.

No description available.

Tropospheric aerosols constitute a major component of the Earth's climate system yet quantitative estimates of their ii impact remain enclosed within wide error limits. Scientific knowledge of aerosol processes and mechanisms is at a relatively low level compared with that of the well-mixed greenhouse gases. Our understanding is hampered by the inhomogeneous spatial and temporal distribution of aeroscols and the complexities of their chemical composition and microphysical properties.

Saccharides and furfural are derived from biomass burning and contribute to aerosol composition. This study examined the potential of saccharides and furfural to be tracers of biomass combustion. Furfural is likely to be oxidized quickly so comparison with saccharides may give a sense of the age of the aerosols in biomass smoke. However, few furfural emissions are available for biomass combustion. Saccharides and furfural were determined in coarse aerosols (diameter> 2.4/lm ) and fine aerosols (diameter < 2.4/lm ) collected in 24 hour periods during different seasons in the United Kingdom and PMIO collected from Thailand and Malaysia including biomass burning areas such as haze episodes and forest fires. Also total suspended particulate matter (TSP) was collected from Taiwan. Saccharides and furfural dominated in fine fractions, especially in the UK autumn. The Principle component analysis showed that the fine mode UK aerosols probably originate from long-range transport emissions from Europe. This was also an important contribution for the crustal group and the biomass burning emission. Sea salt and combustion emission may contribute to coarse mode aerosols. Fraction of saccharides and furfural in aerosols were higher during Southeast Asian haze episodes and forest fires. They were also correlated to potassium and total carbon. Collection of aerosol particles led to blackening on filter papers. The oxidation processes in the atmosphere may lead to more yellowness of aerosols. The yellowness of aerosols collected from forest fires correlated with saccharides and furfural. This may indicate that the organic carbons from forest fires are related to the oxidation process. Although the emission rates of saccharides and furfural from biomass burning were found to have similar levels, furfural was detected at low concentration suggesting loss from atmospheric aerosols. Laboratory experimental simulation suggested furfural is more rapid destroyed by UV, sunlight and ozone than saccharides.

No description available.

The indirect effects of anthropogenic aerosols—through their interactions with clouds—are currently one of the most uncertain perturbations to the radiative energy balance at the top of the atmosphere. A crucial link between aerosol and cloud is that aerosols can act as cloud condensation nuclei (CCN). This microphysical process must be parameterised if the large-scale effects are to be represented in a general circulation model (GCM). Theoretical work presented in this thesis highlights the importance of incorporating the kinetic limitations on droplet formation in aerosol activation parameterisations. HadGEM-UKCA is a GCM, capable of representing the chemical and microphysical aerosol processes required to model CCN accurately. The author has incorporated a Köhler theory based parameterisation of aerosol activation into HadGEM-UKCA, to facilitate quantitative predictions of the indirect aerosol effects. This thesis presents an estimate of the range of uncertainty in such predictions attributable to the choice of parameterisation of the sub-grid-scale variability of vertical velocity. Results of simulations demonstrate that the use of a characteristic updraught velocity cannot replicate results derived with a distribution of vertical velocities, and is to be discouraged in GCMs. Consequently, work focuses on the effect of the variance (<var>σ</var>_w²) of a Gaussian pdf of vertical velocity. Fixed values of <var>σ</var>_w and a configuration in which <var>σ</var>_w depends on turbulent kinetic energy are tested. Results from the mid-range fixed <var>σ</var>_w and TKE-based configurations both compare well with vertical velocity distributions and cloud droplet number concentrations measured in situ. However, the sparse set of available measurements does not provide enough of a constraint to recommend one or the other as the best configuration globally. The radiative flux perturbation (RFP) due to the total effects of anthropogenic aerosol is estimated at −1.7Wm⁻² for the TKE-based configuration. To the extent that it is valid to decouple the individual aerosol effects, the direct effect accounts for approximately −0.6Wm⁻² of the total, the cloud albedo effect −0.8Wm⁻² and the cloud lifetime effect −0.3Wm⁻², indicating that these effects are additive within HadGEM-UKCA. Total aerosol RFP ranges from −1.4Wm⁻² from simulations with <var>σ</var>_w=0.1ms⁻¹, up to −2.0Wm⁻² for <var>σ</var>_w=0.7ms⁻¹. This range of 0.6Wm⁻² corresponds to almost a third of the total estimate of −1.9Wm⁻², obtained with the mid-range value of <var>σ</var>_w=0.4ms⁻¹. Reducing the uncertainty in the parameterisation of <var>σ</var>_w is therefore an important step towards reducing the uncertainty in estimates of the indirect aerosol effects.

This thesis presents a new technique to identify a 2D mask showing the extent of particulate aerosol distributions in satellite imagery. This technique uses a supervised texture classication approach, and utilises data from two distinct satellite sources. The vertical feature mask (VFM) product from the CALIPSO lidar, provides an accurate description of the aerosol content of the atmosphere but has a limited footprint and coverage. The CALIPSO VFM is used to provide training data in order to for classiers to be applied to other imagery, namely data from the spinning enhanced visible and infrared imager (SEVIRI) on the MSG satellite. The output from the classication is a 2D mask representing the locations of the particulate aerosol of interest within the SEVIRI image. This approach has been demonstrated on test cases over land and ocean, and shows a good agreement with other techniques for the detection of particulate aerosol. However, the supervised texture approach provides outputs at a higher resolution than the existing methods and the same approach is applicable over land and ocean and therefore shows the advantages compared to the current techniques. Furthermore, the coverage of the approach can be further extended using signature extension and chain classication. Signature extension was applied to one of the test cases to monitor the same geographical region with temporal extension away from the initial supervised classication. The experiments showed that it was possible to extend the coverage for ±90 minutes from the original classication and indicates the possibility of greater extension over larger temporal windows.