Amino acids, as building blocks of living species, are ubiquitous. Their presence in atmospheric precipitation and aerosols has been noted for many years; however, measurements of their abundance in aerosol are scarce. As a result, relatively little is understood about their sources, and impact on ecological systems and atmospheric processes. In this thesis project, I have made measurements of amino acids and aliphatic amines in aerosol samples collected at three locations (Hong Kong, Nanjing, and Jeju Island, S. Korea) in the Eastern Asia region from 2000 to 2002. The sampling locations ranged from rural surroundings (e.g., Hok Tsui in Hong Kong and Jeju Island) to highly urbanized locations (e.g., Mong Kok in Hong Kong and Nanjing). A set of 14 aerosol samples collected on research ai...[ Read more ]

Amino acids, as building blocks of living species, are ubiquitous. Their presence in atmospheric precipitation and aerosols has been noted for many years; however, measurements of their abundance in aerosol are scarce. As a result, relatively little is understood about their sources, and impact on ecological systems and atmospheric processes. In this thesis project, I have made measurements of amino acids and aliphatic amines in aerosol samples collected at three locations (Hong Kong, Nanjing, and Jeju Island, S. Korea) in the Eastern Asia region from 2000 to 2002. The sampling locations ranged from rural surroundings (e.g., Hok Tsui in Hong Kong and Jeju Island) to highly urbanized locations (e.g., Mong Kok in Hong Kong and Nanjing). A set of 14 aerosol samples collected on research aircraft were also included in this project. Aerosol particles collected on filter substrates were extracted with water. Amino compounds in the water extracts were subsequently derivatized with a fluorescence agent, separated on a high performance liquid chromatogram (HPLC) column, and detected by a fluorescence detector.

The concentrations of total free and hydrolysable amino compounds were found to range from 604-2788 pmol/m³ and 775-3197 pmol/m³. These levels were similar to those observed in continental locations in the U.S., but much lower than those measured over the oceans. Higher levels of amino compounds were observed in samples collected in urban areas in comparison with rural locations. Nanjing had the highest levels and Jeju Island had the lowest levels of amino compounds among all the sampling locations. Among the three sampling locations in Hong Kong, the rural site Hok Tsui had the lowest concentrations whereas the roadside site Mong Kok and the urban site Tsuen Wan had higher concentrations of amino compounds. The aircraft samples also show that the pollution-dominated layer was found to be most abundant in amino compounds. Both the ground-based and aircraft measurements suggested that urban centers were sources for amino compounds in aerosols.

Analysis of size segregated aerosol samples indicated that the aerosol size distribution of amino compounds was bimodal, one major fine mode and one minor coarse mode. The majority of amino compounds were present in particles less than 2.5 μm. This discounts ocean as a major source for aerosol amino compounds since sea salt aerosol materials are mainly in the coarse mode. This also excludes soil dusts as an important source for airborne amino compounds because dust particles are dominated by the coarse mode. It is speculated that the fine mode amino compounds likely come from gas-particle conversion or bioaerosols of small sizes, but the exact pathway has yet to be identified.

The most abundant amino compounds were glycine and methylamine. The few abundant amino compounds were highly correlated in samples collected in Hong Kong, suggesting common sources. The Nanjing samples, however, lacked good correlations among the abundant amino compounds, indicating sources for amino compounds might be location-dependent.

Amino compounds in aerosols are a source of biologically utilizable nitrogen for ecosystems. As water-soluble compounds. they could also act as cloud condensation nuclei; thereby play a role in atmospheric processes that affect global climate and regional visibility. The abundance of amino compounds observed in this project signals that further work is needed to understand the sources of this group of compounds.