Abstracts – Session B4
Interaction of urban air quality and ecosystems
B401 - ORAL-0233: Effects of CO2-ozone-vegetation interactions on global air quality
Amos P. K. Tai1, 2, Anthony Wong1, Shanshan Zhou2
1Earth System Science Programme, Faculty of Science, The Chinese University of Hong Kong, Shatin, Hong Kong 2Graduate Division of Earth and Atmospheric Sciences, Faculty of Science, The Chinese University of Hong Kong, Hong Kong, China
Plant physiological functions such as photosynthesis, stomatal activity and terpenoid production play an important role in shaping the Earth's atmosphere. Changes in plant physiology in response to rising CO2, and tropospheric ozone levels would therefore interfere with land-atmosphere exchange processes (e.g. evapotranspiration, dry deposition, isoprene emission), with ramifications for air quality. Here we develop and integrate several parameterization schemes for CO2-ozone-vegetation coupling into the GEOS-Chem chemical transport model to examine how rising CO2 and ozone damage on vegetation would influence ozone air quality via various pathways. We find that elevated CO2 for year 2050 under the RCP8.5 scenario can significantly suppress isoprene emission (due to the CO2 inhibition effect) and thus reduce surface ozone by up to 6 ppb, but can also reduce dry deposition velocity (due to reduced stomatal conductance) and thus increase surface ozone by up to 6ppb. The effect of enhanced leaf area index (LAI) (due to CO2 fertilization) is much smaller. The combined effect of elevated CO2 via all three pathways is in the range of -1 to +4 ppb, reflecting compensating effects. On the other hand, ozone-induced damage on LAI can lead to an ozone feedback of -1 to +3 ppb, also reflecting compensating effects of reduced dry deposition and isoprene emission. These changes in surface ozone are comparable in magnitude with the effects of climate and land use changes per se, and we therefore suggest that plant physiological changes arising from varying CO2 and ozone levels are important factors that should be accounted for in historical simulations and future projections of air quality.
B402 - ORAL-0386: The atmospheric boundary layer characteristics and air pollution transport over the Kathmandu Valley, Nepal
Saraswati Shrestha1, Ram Prasad Regmi1
1Central Department of Physics, Tribhuvan University, Kirtipur, Nepal
The Kathmandu valley, located in the Middle Hills of Central Nepal Himalaya, has been considered as one of the ideal locations to study the spatial and temporal characteristics of the atmospheric boundary layer and air pollution potential since it is the most populated urban center located at extreme topography, experiencing long-unsolved and unacceptable level of air pollution. The diurnal characteristics of local flows and mixing height over the valley were monitored at the central area of the valley using SODAR and weather stations and the prevailing meteorological flow fields were numerically simulated using WRF modeling system at 1 km x 1 km horizontal grid resolution. The bowl-shaped valley generally remains capped by inversion layer near the surface and also develops a deep cold-air pool with the depth equivalent to the approximate depth of the valley, during the night and morning stable situations. Several numerical simulations, daily forecast in recent months validated with observations over the valley revealed that the valley air mass rarely remains decoupled from the regional air mass during the daytime though nighttime valley air mass generally remains decoupled with the regional air mass from late evening to early morning. Thus, the Kathmandu valley located atop the rather isolated mountainous region in the middle hills of Central Nepal Himalaya has been found to be associated with a complex combination of regional and local-scale meteorological flow fields leading to high air pollution potential during the dry winter season over the valley.
B403 - ORAL-0171: Decadal Change of PAN & O3 levels in Seoul during May and June
In Seoul, the decadal change of PAN and O3 concentrations were examined for the two months of May and June, when O3 concentration is the highest of the year. The measurement sets of PAN and O3 are available for 2004, 2005, 2015, 2016. PAN was measured by a fast GC system coupled with Luminol chemiluminescence.
The hourly maximum PAN and O3 concentrations were 10 ppbv and 123 ppbv in 2004, 8 ppbv and 141 ppbv in 2005, 4.4 ppbv and 143 ppbv in 2015, and 7.5 ppbv and 127 ppbv in 2016, respectively. The mean concentrations of PAN were decreased during the decade. The occurrence of high O3 concentrations (> 100 ppbv, 1 hr average) was more frequent or similar trends were observed between 2004, 2005 and 2015, 2016. As common precursors of PAN and O3, NOx concentrations were slightly decreased. However, the decrease of NOx was mostly due to decrease in NO, leading to higher NO2/NOx ratios. For VOCs, the total concentrations (TVOCs) were evidently decreased but with different proportions in their subclasses. Although the VOCs measurements were made in different sites, the comparison results show the increased fraction of biogenic VOCs in recent years. The different behaviours in PAN and O3 levels for the last decade is mainly associated with increased ratios of NO2/NOx and BVOCs/TVOCs in Seoul.
B404 - ORAL-0262: A forest in the edge of a megacity – oxidation capacity and atmospheric reactivity determined by biosphere-human interactions
Saewung Kim, Alex Guenther, Meehye Lee, Roger Seco, Dasa Gu, Daun Jeong, Dianne Sanchez, Blanca Rodriguez
The complicated interactions between human and forest nearby the urban environments have been studied quite a while. The research outcomes have provided the snapshots of how human influence can cause perturbations in the forest canopy system or how reactive gas emission or deposition from and to the forest canopy can affect regional air-quality. At Taehwa Resaerch Forest located 40 km from the city center of Seoul Metropolitan Area the second largest megacity in the world, we have attempted to examine both directions of interactions between human and forest through the atmosphere. This presentation will focus on the findings from the KORUS-AQ campaign in May to early June of 2016. An extensive trace gas analysis was conducted at the site as a part of the multi-platform field campaign including multiple ground sites and research aircrafts. In the presentation, we will discuss how plant volatile affect in canopy and out of canopy atmospheric composition and its photochemistry in addition to how those photochemical products consequently cause changes in plant volatile emission profiles.
B405 - POSTER-0218: Bioaccessibility and health risk of trace elements in fine particulate matter using different simulated body fluids
Dongyang Nie1, Mindong Chen
Long-term exposure PM2.5-bound metal have been proved to cause hazardous effects to human health. In this study, the bioaccessibility and health risk of trace elements in fine particulate matter were investigated. Four kinds of simulated body fluids were employed to extract the PM2.5 for simulating different exposure routes (inhalation, ingestion and dermal contact). Phosphate buffered saline(PBS) and the artificial lysosomal fluid(ALF) were used as surrogate human lung fluids, artificial sweat(AS) was used for simulating dermal contract, artificial gastric juice was employed to mimic human digestion. It showed that many trace elements were less soluble in PBS than other body fluid, especially for Pb Al. Cu, Mn, V, As were observed to be the most soluble trace elements in all simulated body fluids. The United States Environmental Protection Agency (USEPA) human health risk assessment model was used to assess the carcinogenic and non-carcinogenic effects. The results showed the carcinogenic risks from As, Cr, and Pb were higher than 10-6(an acceptable level for human health) especially for children, indicating that there were potential carcinogenic risks posed by these toxic elements. The high hazard quotient value for As, Cr, and Pb were also observed to children. It suggested that the sampling site was experiencing trace elements pollution, especially for As, Cr, and Pb.
B406 - POSTER-0310: High O3 episodes in Seoul during early summer 2016
희정 김, Meehye Lee, Seogju Cho, Jinsang Jung, Gangwoong Lee
To determine controlling factors of ozone (O3) formation in Seoul Metropolitan Area (SMA), H2O2, PAN, and HONO were measured in conjunction with O3 and its precursors. The experiment was conducted at Olympic Park in Seoul during May12~June15, 2016.
For the entire experiment period, the high O3 event of hourly mean over 100 ppbv occurred on May 20, 23, 25, 29 and 30 and June 10 and 14. These events were different in meteorological conditions, precursor strengths, and chemical characteristics. Weather conditions are more favourable for air stagnation in June, leading to high temperature and high VOCs (Volatile Organic Compounds) concentrations, particularly BVOCs (Biogenic VOC), and consequently high O3 concentrations. During May 27, 29~30, O3 was enhanced with aerosols, when air was coming from the Yellow Sea. This event was concurrently observed in the Yellow Sea region from the ship, DC 8, and Changdao Island in Bohai Sea. Ozone was highly elevated around 7 PM on May 20, of which mechanism is not clear. However, it indicates the important role of boundary layer dynamics in O3, which was not well understood.