| dc.description.abstract | This thesis comprises two parts. The first part aims to developing monitoring and applications of ambient volatile organic compounds (VOCs), which contains two subjects, i.e., studying the composition of pure traffic emissions and interpreting the occurrence of air pollution events in southern Taiwan. The second part aims to develop monitoring capabilities of greenhouse gases (GHGs) at a high mountain station and to add these gases to the list of routine monitoring.
The first subject of the VOC work is to study the composition of vehicular emissions and the relationship between traffic speed and chemical composition. To obtain pure traffic emissions without interferences from other sources, a long-tunnel tunnel (12.9 km) was exploited in the study. A series of non-methane hydrocarbons (NMHCs) and carbon monoxide (CO) in multiple air samples collected from a moving vehicle inside the tunnel were analyzed. Instead of calculating emission factors as appeared in most of the related works in the literature, the compositional changes in emission at various speeds were discussed in a relative manner by normalizing individual NMHCs with CO concentrations to obtain relative emissions. Subsequently, the effects on ozone formation arisen from the compositional changes at different speeds were discussed. Results show that, at the slowest speed (45 km hr-1) due to traffic congestion in the tunnel, the group of alkanes dominates the NMHC composition. As the speed increases (75-85 km hr-1), alkenes and aromatics become the dominant constituents of the NMHC composition. Although, on the per-unit-mass basis, alkenes and aromatics have higher maximum increment reactivity (MIR) than alkanes, the much greater emissions at the slowest speed still induce the largest ozone forming potential as a whole. The novelties of this study lie in the following aspects: 1. Long tunnels are ideal for obtaining pure vehicular emissions, which is more advantageous than performing emission studies in shorter tunnels or with chassis dynamometers; 2. Multiple sampling along the long tunnel can better represent pure traffic emissions with minimal interferences from other non-vehicular sources as compared to measurements in short tunnels; 3. The use of NMHC/CO ratios can eliminate the factor of vehicle densities, enabling more straightforward comparison between different datasets.
The second subject of the VOC work is to study the cause of high-ozone episodes that frequently occurred in southern Taiwan. A case study in springtime was chosen for the study. The VOC monitoring was coupled with model simulations (PAMS-AQM) to help interpret dispersion of air pollutants, and toluene was employed as the surrogate pollutant in model simulations to display pollutants movements. Results show that when strong northwesterly winds prevail, pollutants are blown westwards to the sea not affecting the northern counties. In contrast, when the local circulation dominates weather conditions, pollutants are blown towards inland areas and, thus, the southern cities are more prone to pollution episodes. This work is one of the very few studies in the literature that coupled model simulations with VOC field measurements, which successfully demonstrates the transport of primary pollutants and the formation of secondary pollutants such as ozone during a pollution episode.
The second part of the thesis is to establish the measurement capabilities of GHGs at a high-mountain background station (Lulin Atmospheric background Station, LABS) using cavity ringdown spectrometry (CRDS) to routinely monitor carbon two major GHGs, namely dioxide (CO2) and methane (CH4). Our in-situ observations of CO2 and CH4 were found to be rather consistent with the NOAA flask results in terms of seasonal variations and average concentrations. The gradual increase in atmospheric CO2 concentrations at LABS also agreed well with global observations, suggesting the GHG observations are representative of this geophysical region. Despite the general agreement with other global stations, the variability was found to be much greater than that at other global stations, implying complex influences from local or long-range transport. To decipher the mechanisms embedded in the variability could make LABS a unique asset in terms of global observations of GHGs. | en_US |