The tropospheric abundances, emissions, and transport of halogenated substances on regional and global scales

The primary aim of this thesis was to use models to study the (a) regional emissions of very short-lived (i.e. chlorinated VSLS) and short-lived (i.e. methyl halides) halogenated gases, as well as (b) global emissions of long-lived halogenated gases (i.e. CFC-114 & CFC-114a). The 3-D dispersion model was employed to determine the impact of different source types and regions on the variability of halogenated gases measured during the campaigns in Taiwan and Bachok, Malaysia. On the other hand, the 2-D global model was used for estimating the emissions of CFC-114 and -114a in archived remote Southern Hemispheric tropospheric air and firn air data. Overall, this thesis has demonstrated that the measured chlorinated VSLS and methyl halides were observed at significantly high abundances. In addition, the quantitative analyses of the NAME backwards trajectories (i.e. using ArcGIS-generated shapefile and emissions data of carbon monoxide (CO) taken from Representative Concentration Pathway 8.5) and the usage of the cold surge index have further shed some light on the potential sources of emission & regions and transport of halogenated gases; these in turn could inform as well as guide future campaigns. Importantly, the studies highlighted the important roles of the (a) Northeast Monsoon’s cold surges and (b) East Asian and South East Asian emissions in the enhancements of halogenated substances levels in that regions. In addition, this thesis presented the first long-term trends and emissions of CFC-114 and-114a. The mixing ratios of both isomers were no longer increasing significantly but significant global atmospheric emissions have persisted until at least 2014, suggesting a need for continual efforts to ensure that these substances eventually disappear from the atmosphere. Evidently, complementary ground-based observations of the Taiwanese air samples in Taiwan suggested the presence of persistent emissions of CFC-114a in East Asia

Levoglucosan as an Indicator of Biomass Burning from Selected Tropical Plants

South East Asia has been recognized as one of the region most affected by atmospheric haze from biomass burning and the combustion of various plants. The distribution of atmospheric aerosols from biomass burning itself can be determined through the level of levoglucosan found in the atmosphere. In this study, the amount of levoglucosan produced by five selected tropical plants after combustion processes was determined using the modified anthrone-sulfuric colorimetric method. The results showed that the concentration of levoglucosan in the plant soot (after combustion) ranged from between 0.49 ± 0.28 mg/g to 10.51 ± 4.47 mg/g. Among the five plants, Oryza sativa was found to have the highest levoglucosan content and the amount of levoglucosan produced by biomass burning was found to be influenced by the photo oxidation processes e.g. by ultra violet radiation and ozonization

Trends and emissions of six perfluorocarbons in the Northern Hemisphere and Southern Hemisphere

Perfluorocarbons (PFCs) are potent greenhouse gases with global warming potentials up to several thousand times greater than CO2 on a 100-year time horizon. The lack of any significant sinks for PFCs means that they have long atmospheric lifetimes of the order of thousands of years. Anthropogenic production is thought to be the only source for most PFCs. Here we report an update on the global atmospheric abundances of the following PFCs, most of which have for the first time been analytically separated according to their isomers: c-octafluorobutane (c-C4F8), n-decafluorobutane (n-C4F10), n-dodecafluoropentane (n-C5F12), n-tetradecafluorohexane (n-C6F14), and n-hexadecafluoroheptane (n-C7F16). Additionally, we report the first data set on the atmospheric mixing ratios of perfluoro-2-methylpentane (i-C6F14). The existence and significance of PFC isomers have not been reported before, due to the analytical challenges of separating them. The time series spans a period from 1978 to the present. Several data sets are used to investigate temporal and spatial trends of these PFCs: time series of air samples collected at Cape Grim, Australia, from 1978 to the start of 2018; a time series of air samples collected between July 2015 and April 2017 at Tacolneston, UK; and intensive campaign-based sampling collections from Taiwan. Although the remote “background” Southern Hemispheric Cape Grim time series indicates that recent growth rates of most of these PFCs are lower than in the 1990s, we continue to see significantly increasing mixing ratios that are between 6 % and 27 % higher by the end of 2017 compared to abundances measured in 2010. Air samples from Tacolneston show a positive offset in PFC mixing ratios compared to the Southern Hemisphere baseline. The highest mixing ratios and variability are seen in air samples from Taiwan, which is therefore likely situated much closer to PFC sources, confirming predominantly Northern Hemispheric emissions for most PFCs. Even though these PFCs occur in the atmosphere at levels of parts per trillion molar or less, their total cumulative global emissions translate into 833 million metric tonnes of CO2 equivalent by the end of 2017, 23 % of which has been emitted since 2010. Almost two-thirds of the CO2 equivalent emissions within the last decade are attributable to c-C4F8, which currently also has the highest emission rates that continue to grow. Sources of all PFCs covered in this work remain poorly constrained and reported emissions in global databases do not account for the abundances found in the atmosphere

Enhanced chlorinated very short-lived substances in South East Asia:Potential source regions and source types

Enhancements of the mixing ratios of short-lived halogenated gases were observed in air samples collected at Bachok Marine Research Station (BMRS), Peninsular Malaysia during Northern Hemisphere winters in 2013/2014 and 2015/2016. This study investigates the potential source regions and source types that influenced the variability in chlorinated very short-lived substances (Cl-VSLS) [dichloromethane, 1,2-dichloroethane, trichloromethane, tetrachloroethene] and methyl halides [methyl chloride and methyl bromide]. The UK Met Office’s Numerical Atmospheric Modelling Environment (NAME) dispersion model, was used for tracking the origin of air masses arriving at BMRS. For the purpose of identifying possible sources of these compounds, carbon monoxide (CO) emission data taken from the Representative Concentration Pathway 8.5 were used along with NAME footprints to calculate modelled CO mixing ratios. A correlation analysis between the mixing ratios of measured compounds and the modelled CO from various emission sectors was perform to assess the extent to which emission sectors might be related to the mixing ratios of halogenated gases. The results show that the events of higher mixing ratios were associated with air masses, especially from East China. During the 2013/2014 campaign, the modelled CO from industrial, solvents and agriculture (waste burning on fields) were significantly correlated with the mixing ratios of Cl-VSLS (R > 0.7) and methyl halides (R > 0.40). During the 2015/2016 campaign, the strength of these correlations reduced for Cl-VSLS (R > 0.5) and with no significant correlations for methyl halides. Instead, mixing ratios of methyl halides were correlated (R=0.4) with modelled CO from forest burning. This work provides evidence that East and South East Asia act as important sources of halogenated gases. This is of significant given the proximity of these regions to prevalent deep convection which can rapidly transport these halogen-containing gases into the stratosphere and impact the ozone layer

Colourimetric determination of features of an air sampling technique optimal for detection of surfactants

Surfactants in the atmosphere may act as cloud condensation nuclei, with a potentially negative impact on the global climate. Therefore, accurate determination of surfactants is crucial in order to investigate the possible effects of surfactants on the atmosphere. The aim of this study was to identify the optimum sampling method for measuring the maximum quantity of surfactants present in ambient air. Air samples were collected using a range of air sampling pumps that were made to vary in terms of flow rate, storage period, type of absorbing solution and the characteristics of the impinger tube. Samples obtained were analysed by colourimetry for anionic and cationic surfactants as methylene blue-active substances (MBAS) and disulphine blue-active substances (DBAS), respectively. Absorbance was measured at 650 nm for MBAS and 628 nm for DBAS using UV-visible spectrophotometer. We found that the optimum sampling method consisted of an absorbent solution (deionised water, buffer solution and methylene blue/disulphine blue solution) with the flow rate of 1.0 L/min. The concentration of surfactants in all sampling methods remained constant regardless of the storage period (1 day and 4 days), indicating that surfactants in the absorbing solution are quite stable. Covering the impinger tube was shown to influence the amount of both anionic and cationic surfactants detected

Atmospheric microplastic transport and deposition to urban and pristine tropical locations in Southeast Asia

Atmospheric microplastic transport is an important delivery pathway with the deposition of microplastics to ecologically important regions raising environmental concerns. Investigating atmospheric delivery pathways and their deposition rates in different ecosystems is necessary to understanding its global impact. In this study, atmospheric deposition was collected at three sites in Malaysia, two urban and one pristine, covering the Northeast and Southwest monsoons to quantify the role of this pathway in Southeast Asia. Air mass back trajectories showed long-range atmospheric transport of microplastics to all sites with atmospheric deposition varying from 114 to 689 MP/m2/day. For the east coast of Peninsular Malaysia, monsoonal season influenced microplastic transport and deposition rate with peak microplastic deposition during the Northeast monsoon due to higher wind speed. MP morphology combined with size fractionation and plastic type at the coastal sites indicated a role for long-range marine transport of MPs that subsequently provided a local marine source to the atmosphere at the coastal sites

CONCENTRATION AND FLUX OF ATMOSPHERIC SURFACTANTS FROM COASTAL WATERS

This study tries to determine the concentration of sea surface microlayer from different coastal environments (Port Dickson, Negeri Sembilan and Perhentian Island, Terengganu). The concentration of surfactants in both sea surface microlayer and atmospheric aerosols were analysed by using colorimetric method as methylene blue active substances (MBAS) and diethyl violet active substances (DBAS). The results indicated that the concentration of surfactants as MBAS (0.421 +/- 0.040 imol l-1) and DBAS (0.294 +/- 0. 123 imol l-1) were still at the natural concentration level. The flux of surfactants from sea surface microlayer is expected around 2.3 Mmol yr-1 compared to the amount of 1300 Mmol yr-1 surfactants in atmospheric aerosols around marine ecosystem

Rekod jangka panjang kepekatan metana di Malaysia

Gas metana (CH4) adalah gas rumah hijau yang menyebabkan perubahan iklim dan pemanasan dunia. Kajian CH4 dijalankan untuk melihat tren pelepasan CH4 di Malaysia dalam satu jangka masa yang panjang (10 tahun) dari tahun 2000 hingga 2009 dan menilai hubungan CH4 dengan ozon permukaan (O3). Data CH4 daripada 19 stesen pemantauan kualiti udara automatik berterusan Jabatan Alam Sekitar (JAS) di Malaysia telah dianalisis menggunakan analisis statistik dan korelasi Pearson. Hasil kajian mendapati nilai bacaan kepekatan purata bulanan CH4 tertinggi dicatatkan di stesen Larkin, Johor Bahru iaitu 2.61±0.54 ppm. Nilai purata kepekatan CH4 berdasarkan data yang direkodkan di semua stesen di Malaysia adalah 2.00 ppm. Taburan kepekatan CH4 yang lebih tinggi didapati tertumpu di kawasan bandar dan kawasan perindustrian di Selangor, Melaka dan Johor. Analisis korelasi bagi menentukan hubungan CH4 dengan bahan pencemar O3 mendapati 15 stesen menunjukkan korelasi positif yang sangat kecil dan lemah (r 0.05). Stesen Shah Alam didapati menunjukkan korelasi CH4 paling tinggi dengan O3 berbanding stesen lain. Pengetahuan asas berkenaan CH4 dalam udara ambien Malaysia yang ditunjukkan dalam kajian ini boleh digunakan untuk menilai potensi impak CH4 terhadap alam sekitar, perubahan iklim dan kesihatan manusia