No abstract

Recent biomass burning in Southeast Asia has raised global concerns over its adverse effects on visibility, human health, and global climate. The concentrations of total suspended particles (TSPs) and other vapor-phase pollutants (CO and ozone) were monitored at Lulin, an atmospheric background station in central Taiwan in 2008. To evaluate the long-range transport of persistent organic pollutants (POPs) during the Southeast Asia biomass burning event, the atmospheric polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) were also measured at Lulin station. The atmospheric PCDD/F and TSP concentrations measured at Lulin station ranged from 0.71-3.41 fg I-TEQ/m(3) and 5.32-55.6 microg/m(3), respectively, during the regular sampling periods. However, significantly higher concentrations of PCDD/Fs, TSPs, CO, and ozone were measured during the spring season. These high concentrations could be the result of long-range transport of the products of Southeast Asia biomass burning. During the Southeast Asia biomass burning event (March 18-24, 2008), an intensive observation program was also carried out at the same station. The results of this observation program indicated that the atmospheric PCDD/F concentration increased dramatically from 2.33 to 390 fg I-TEQ/m(3) (March 19, 2008). The trace gas (CO) of biomass burning also significantly increased to 232 ppb during the same period, while the particle-bound PCDD/Fs in the TSP increased from 28.7 to 109 pg I-TEQ/g-TSP at Lulin station during the burning event. We conclude that there was a significant increase in the PCDD/F concentration in ambient air at a high-altitude background station in central Taiwan during the Southeast Asia biomass burning event.

Dioxin and dioxin-like compounds such as polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) are persistent organic pollutants (POPs) generated through human activities. In recent times, extreme weather events such as wild fires have significantly affected the remobilization and successive bioavailability of PCDD/Fs.

One unique long‐range transport event with multiple layers of aerosol plumes was observed over Taiwan during 29–31 March 2006. A synergy of ground‐based observation, remote sensing, and backward trajectory simulation collectively indicated the high‐altitude (above 3 km) plume originated from biomass burning in Southeast Asia while the midaltitude (around 0.8–2 km) plume was attributed to dust from the Gobi Desert. Aerosol optical properties measured at a low‐altitude site were characterized of abundant coarse mode particles and increased single scattering albedo as a function of increased wavelength, indicating the influence from dust particles. While at a high mountain site (elevation of ~3 km), aerosol optical depth was elevated by a factor of 3–4 compared to its background value and mainly comprised of fine particles. It was diagnosed that the high‐altitude aerosols were influenced by the transported smoke plumes but exempted from dust. Simulation of the meteorological conditions against a Taiwan‐wide meteorology network showed strong near surface temperature rise of more than 2° during this long‐range transport event as well as for the vertical temperature profiles. Both dust and biomass burning aerosol plumes via long‐range transport contributed significantly to the atmospheric warming, resulting in strong instantaneous aerosol radiative forcing of 46.0 W/m2 in the atmosphere. A “double dome” warming effect mechanism was proposed that both biomass burning and dust plumes above the boundary layer could efficiently reserve the solar energy and heat the lower troposphere.

High elevation ecosystems are particularly sensitive to environmental change. Mountain agriculture is extending to areas at high elevations in Taiwan but the effects on nutrient cycling of the surrounding ecosystems are largely unknown. We examined precipitation chemistry at Piluchi Experimental Forest in central Taiwan to evaluate the contributions of local air pollution and long-range transport of air pollutants on nutrient cycling at this seemingly remote forest. Sea-salt aerosols and anthropogenic pollutants resulting from long-range transport of air pollutants and mountain agriculture activities are the key factors affecting precipitation chemistry at Piluchi Experimental Forest. Precipitation chemistry was dominated by ions of oceanic origin in the summer and by anthropogenic pollutants SO 4 2-, NO 3 -and NH 4 ? in the winter and spring, the northeast monsoon season. The much higher concentrations of S and N in the northeast monsoon season than the summer suggest a substantial contribution from long-range transport as the prevailing air masses moved from inland China and passed over the industrialized east coast of China before arriving in Taiwan. The very high concentration of NH 4 ? (22 leq L -1 ) in the spring, when the local application of N-containing fertilizers was high, signifies the influences of mountain agriculture. Despite very low concentrations relative to other sites in Taiwan, annual input of NH 4 ? (3.6 kg ha -1 year -1 ), NO 3 -(7.2 kg ha -1 year -1 ) and SO 4 2-(10 kg ha -1 year -1 ) via precipitation was substantial suggesting that high elevation ecosystems of Taiwan are not free from the threat of atmospheric deposition of pollutants.