Determining ground-level composition and concentration of particulate matter across regional areas using the Himawari-8 satellite

Speciated ground-level aerosol concentrations are required to understand and mitigate health impacts from dust storms, wildfires and other aerosol emissions. Globally, surface monitoring is limited due to cost and infrastructure demands. While remote sensing can help estimate respirable (i.e. ground level) concentrations, current observations are restricted by inadequate spatiotemporal resolution, uncertainty in aerosol type, particle size, and vertical profile. One key issue with current remote sensing datasets is that they are derived from reflectances observed by polar orbiting imagers, which means that aerosol is only derived during the daytime, and only once or twice per day. Sub-hourly, infrared (IR), geostationary data, such as the ten-minute data from Himawari-8, are required to monitor these events to ensure that sporadic dust events can be continually observed and quantified. Newer quantification methods using geostationary data have focussed on detecting the presence, or absence, of a dust event. However, limited attention has been paid to the determination of composition, and particle size, using IR wavelengths exclusively. More appropriate IR methods are required to quantify and classify aerosol composition in order to improve the understanding of source impacts. The primary research objectives were investigated through a series of scientific papers centred on aspects deemed critical to successfully determining ground-level concentrations. A literature review of surface particulate monitoring of dust events using geostationary satellite remote sensing was undertaken to understand the theory and limitations in the current methodology. The review identified (amongst other findings) the reliance on visible wavelengths and the lack of temporal resolution in polar-orbiting satellite data. As a result of this, a duststorm was investigated to determine how rapidly the storm passed and what temporal data resolution is required to monitor these and other similar events. Various IR dust indices were investigated to determine which are optimum for determining spectral change. These indices were then used to qualify and quantitate dust events, and the methodology was validated against three severe air quality events of a dust storm; smoke from prescribed burns; and an ozone smog incident. The study identified that continuous geostationary temporal resolution is critical in the determination of concentration. The Himawari-8 spatial resolution of 2 km is slightly coarse and further spatial aggregation or cloud masking would be detrimental to determining concentrations. Five dual-band BTD combinations, using all IR wavelengths, maximises the identification of compositional differences, atmospheric stability, and cloud cover and this improves the estimated accuracy. Preliminary validation suggests that atmospheric stability, cloud height, relative humidity, PM2.5, PM10, NO, NO2, and O3 appear to produce plausible plumes but that aerosol speciation (soil, sea-spray, fires, vehicles, and secondary sulfates) and SO2 require further investigation. The research described in the thesis details the processes adopted for the development and implementation of an integrated approach to using geostationary remote sensing data to quantify population exposure (who), qualify the concentration and composition (what), assess the temporal (when) and spatial (where) concentration distributions, to determine the source (why) of aerosols contribution to resulting ground-level concentration

Impact of High Concentrations of Saharan Dust Aerosols on Infrared-Based Land Surface Temperature Products

An analysis of three operational satellite-based thermal-infrared land surface temperature (LST) products is presented for conditions of heavy dust aerosol loading. The LST products are compared against ERA5’s skin temperature (SKT) across the Sahara Desert and Sahel region, where high concentrations of dust aerosols are prevalent. Large anomalous differences are found between satellite LST and ERA5’s SKT during the periods of highest dust activity, and satellite–ERA5 differences are shown to be strongly related to dust aerosol optical depth (DuAOD) at 550 nm, indicating an underestimation of LST in conditions of heavy dust aerosol loading. In situ measurements from two ground stations in the Sahel region provide additional evidence of this underestimation, showing increased biases of satellite LST with DuAOD, and no significant dependence of ERA5’s SKT biases on dust aerosol concentrations. The impact of atmospheric water vapor content on LST and SKT is also examined, but dust aerosols are shown to be the primary driver of the inaccurate LSTs observed. Based on comparisons with in situ data, we estimate an aerosol-induced underestimation of LST of approximately 0.9 K for every 0.1 increase in DuAOD. Analysis of brightness temperatures (BTs) in the thermal infrared atmospheric window reveals that dust aerosols have the opposite effect on BT differences compared to water vapor, leading to an underestimation of atmospheric correction by the LST retrieval algorithms. This article highlights a shortcoming of current operational LST retrieval algorithms that must be addressed

Identifying mineral dust emission sources in the Middle East using remote sensing techniques

This investigation presents a new high-resolution mineral dust climatology for the Middle East, describing the dust emission source of over 27,000 dust emission events during the period 2006 – 2013. The inventory was derived from the dust RGB product of the Spinning Enhanced Visual and InfraRed Imager (SEVIRI) on-board Meteosat’s second-generation satellite (MSG). Mineral dust emissions were derived from visual inspection of the SEVIRI scenes, which have 4-5 km2 spatial and 15-minute temporal resolution. The location of every emission event was recorded in a database, along with time and trajectory of dust movement. This is an improvement on previous studies, which derive dust source areas from the daily observations of Aerosol Optical Depth whose maxima do not necessarily coincide with sources of emissions, producing more accurate information on the location of the important dust sources in the region. Results showed that dust sources are constrained to relatively small areas, with 23% of dust emissions generated from areas covering just 1% of the total land surface of the Middle East. Important sources include the Tigris-Euphrates flood plains of Iraq and Syria, Western and Northern Saudi Arabia and the Sistan Basin in Eastern Iran. The Tigris-Euphrates flood plain was the most active dust region, producing 37% of all dust events. Here, agricultural surfaces, especially those producing rain-fed wheat and barley appear to be particularly sensitive to drought conditions, with greatest dust emission frequency at the peak of the 2007 – 2009 drought – the most severe drought in instrumental history. Normalised Difference Vegetation Index (NDVI) data was acquired from the Moderate Resolution Imaging Spectrodiometer (MODIS) (MOD13A2) 1km database and correlated with dust emission frequency data in the region of greatest dust activity. These dust emission ‘hotspots’ showed a significant correlation between vegetation cover and dust emission frequency, with increased vegetation cover during non-drought years producing a marked decrease in dust emission frequency. The southern areas of the Arabian Peninsula recorded very few dust emission observations, contrasting directly to many previous studies, which do not use such high temporal resolution data. The activation and frequency of dust emissions are characterised by strong seasonality developing in response to specific synoptic conditions. ERA Interim reanalysis data were used to characterise synoptic conditions on identified dusty days, demonstrating a concurrent increase in dust emission frequency with intensifying summer (JJA) Shamal (northerly) winds over the Arabian Peninsula

New insights into dust aerosol entrainment mechanisms from satellite/ground-based data, climate modeling, and wind-tunnel experiments

Atmospheric dust aerosols have implications for Earth’s radiation budget, biogeochemical cycles, hydrological cycles, human health, and visibility. Currently, there is a considerable mismatch between climate model simulations and observations in representing the dust cycle in terms of emission, transport, and deposition. This mismatch is related partly to our inadequate understanding of the complex dust emission processes and partly to the way these processes are represented in climate models. In this work, we examine these problems from various perspectives with an interdisciplinary approach by integrating wind-tunnel experiments, geomorphological mapping, satellite observations, land surface modeling, atmospheric reanalysis, and fully coupled earth system modeling. The primary science contributions of this work are summarized here. First, we developed a detailed regional land cover map of the dust belt, the Middle East and North Africa. The developed map can be integrated in any regional dust models for better representing the spatial variation in dust source erodibility. We also developed a new observation-based soil erodibility map in global scale based on the correlation between reanalysis surface winds and satellite-observed aerosol optical depth data (AOD). Second, we integrated the developed observation-based erodibility map into the Community Earth System Model (CESM) and evaluated CESM’s performance in simulating mineral dust emission over the dust belt. Results show that the new erodibility map improves dust simulations in terms of AOD/dust optical depth (DOD) and the CESM captures large scale dust storms reasonably well when the winds are nudged towards ERA-Interim reanalysis data. Third, we conducted wind tunnel experiments and explored some of the lesser understood physical mechanisms of dust emission in sandblasting and direct aerodynamic entrainment. Results indicate that surface roughness can control dust emission in direct aerodynamic entrainment and that dust emission by direct aerodynamic entrainment can be significant under certain conditions compared to sandblasting. Lastly, we develop a principal component analysis based technique to extract locally mobilized dust component from the AOD data, which otherwise represent a mixture of several aerosol types and advected dust/aerosols.Geological Science