Significant impact of the East Asia monsoon on ozone seasonal behavior in the boundary layer of Eastern China and the west Pacific region

The impact of the East Asia monsoon on the seasonal behavior of O<sub>3</sub> in the boundary layer of Eastern China and the west Pacific region was analyzed for 2004–2006 by means of full-year nested chemical transport model simulations and continuous observational data obtained from three inland mountain sites in central and eastern China and three oceanic sites in the west Pacific region. The basic common features of O<sub>3</sub> seasonal behaviors over all the monitoring sites are the pre- and post-monsoon peaks with a summer trough. Such bimodal seasonal patterns of O<sub>3</sub> are predominant over the region with strong summer monsoon penetration, and become weaker or even disappear outside the monsoon region. The seasonal/geographical distribution of the pre-defined monsoon index indicated that the East Asia summer monsoon is responsible for the bimodal seasonal O<sub>3</sub> pattern, and also partly account for the differences in the O<sub>3</sub> seasonal variations between the inland mountain and oceanic sites. Over the inland mountain sites, the O<sub>3</sub> concentration increased gradually from the beginning of the year, reached a maximum in June, decreased rapidly to the summer valley in July or August, and then peaked in September or October, thereafter decreased gradually again. Over the oceanic sites, O<sub>3</sub> abundance showed a similar increasing trend beginning in January, but then decreased gradually from the end of March, followed by a wide trough with the minimum in July and August and a small peak in October or November. A sensitivity analysis performed by setting China-emission to zero revealed that the chemically produced O<sub>3</sub> from China-emission contributed substantially to the O<sub>3</sub> abundance, particularly the pre- and post-monsoon O<sub>3</sub> peaks, over China mainland. We found that China-emission contributed more than 40% to total boundary layer O<sub>3</sub> during summertime (60–70% in July) and accounted for about 40 ppb of each peak value over the inland region if without considering the effect of the nonlinear chemical productions. In contrast, over the oceanic region in the high monsoon index zone, the contribution of China-emission to total boundary layer O<sub>3</sub> was always less than 20% (<10 ppb), and less than 10% in summer

Impact of open crop residual burning on air quality over Central Eastern China during the Mount Tai Experiment 2006 (MTX2006)

The impact of open crop residual burning (OCRB) on O<sub>3</sub>, CO, black carbon (BC) and organic carbon (OC) concentrations over Central Eastern China (CEC; 30–40° N, 111–120° E), during the Mount Tai Experiment in 2006 (MTX2006) was evaluated using a regional chemical transport model, the Models–3 Community Multiscale Air Quality Modeling System (CMAQ). To investigate these pollutants during MTX2006 in June 2006, daily gridded OCRB emissions were developed based on a bottom-up methodology using land cover and hotspot information from satellites. This model system involving daily emissions captured monthly–averages of observed concentrations and day-to-day variations in the patterns of O<sub>3</sub>, CO, BC and OC at the summit of Mount Tai (36° N, 117° E, 1534 m a.s.l., Shandong Province of the People's Republic of China) with high correlation coefficients between the model and observations ranging from 0.55 to 0.69. These results were significantly improved from those using annual biomass burning emissions. For monthly-averaged O<sub>3</sub>, the simulated concentration of 80.8 ppbv was close to the observed concentration (81.3 ppbv). The MTX2006 period was roughly divided into two parts: 1) polluted days with heavy OCRB in the first half of June; and 2) cleaner days with negligible field burning in the latter half of June. Additionally, the first half of June was characterized by two high-pollution episodes during 5–7 and 12–13 June, separated by a relatively cleaner intermediate period during 8–10 June. In the first high-pollution episode, the model captured the high O<sub>3</sub>, CO, BC and OC concentrations at the summit of Mount Tai, which were associated with OCRB over southern CEC and subsequent northward transport. For this episode, the impacts of OCRB emissions on pollutant concentrations were 26% (O<sub>3</sub>), 62% (CO), 79% (BC) and 80% (OC) at the summit of Mount Tai. The daily OCRB emissions were an essential factor in the evaluation of these pollutants during MTX2006. These emissions have a large impact not only on primary pollutants but also on secondary pollutants, such as O<sub>3</sub>, in the first half of June over northeastern Asia. The model reproduced reasonably well the variation of these pollutants in MTX2006, but underestimated daily averages of both CO and BC by a factor of 2, when using emission data from almost solely anthropogenic fuel sources in the latter half of the observation period when field burning can be neglected

Mass concentrations of black carbon measured by four instruments in the middle of Central East China in June 2006

Author name used in this publication: Gao, J.Author name used in this publication: Wang, T.2008-2009 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Near-ground ozone source attributions and outflow in central eastern China during MTX2006

A 3-D regional chemical transport model, the Nested Air Quality Prediction Model System (NAQPMS), with an on-line tracer tagging module was used to study the source of the near-ground (<1.5 km above ground level) ozone at Mt. Tai (36.25° N, 117.10° E, 1534 m a.s.l.) in Central Eastern China (CEC) during the Mount Tai eXperiment 2006 (MTX2006). The model reproduced the temporal and spatial variations of near-ground ozone and other pollutants, and it captured highly polluted and clean cases well. The simulated near-ground ozone level over CEC was 60–85 ppbv (parts per billion by volume), which was higher than values in Japan and over the North Pacific (20–50 ppbv). The simulated tagged tracer data indicated that the regional-scale transport of chemically produced ozone over other areas in CEC contributed to the greatest fraction (49%) of the near-ground mean ozone at Mt. Tai in June; in situ photochemistry contributed only 12%. Due to high anthropogenic and biomass burning emissions that occurred in the southern part of the CEC, the contribution to ground ozone levels from this area played the most important role (32.4 ppbv, 37.9% of total ozone) in the monthly mean ozone concentration at Mt. Tai; values reached 59 ppbv (62%) on 6–7 June 2006. The monthly mean horizontal distribution of chemically produced ozone from various ozone production regions indicated that photochemical reactions controlled the spatial distribution of O<sub>3</sub> over CEC. The regional-scale transport of pollutants also played an important role in the spatial and temporal distribution of ozone over CEC. Chemically produced ozone from the southern part of the study region can be transported northeastwardly to the northern rim of CEC; the mean contribution was 5–10 ppbv, and it reached 25 ppbv during high ozone events. Studies of the outflow of CEC ozone and its precursors, as well as their influences and contributions to the ozone level over adjacent regions/countries, revealed that the contribution of CEC ozone to mean ozone mixing ratios over the Korean Peninsula and Japan was 5–15 ppbv, of which about half was due to the direct transport of ozone from CEC and half was produced locally by ozone precursors transported from CEC

Trans-Eurasian transport of ozone and its precursors

Long-range transport of air across the European and Asian continents brings substantial quantities of ozone and other oxidants to northeast Asia from upwind sources over Europe and North America. This transport differs significantly from that over the Pacific and Atlantic Oceans because of weaker and less frequent frontal systems over the continent and because of weaker convective lifting over European sources. Slower O-3 formation, faster destruction at low altitudes, and greater deposition over continental regions lead to Europe having a smaller impact on O-3 than other source regions. We present chemical transport model studies of the formation and transport of O3 from European precursor sources and investigate the extent of their impacts over Eurasia. We focus on measurement sites at 100degreesE, representing the inflow to east Asia on which regional pollutant sources build, and on northeast Asia, which may be directly affected by transport across Eurasia. The seasonality in O-3 production over Europe is simulated well, and transport principally in the boundary layer propagates these changes in O-3 over Eurasia, leading to monthly mean impacts at Mondy, Siberia, of 0.5-3.5 ppbv. Impacts over Japan are smaller, 0.2-2.5 ppbv, and are very similar to those from North American sources, which dominate at higher altitudes. By following the effect of daily emissions independently, we clearly demonstrate that this greater North American impact is associated with lifting over the Atlantic. European and North American sources contribute to background O-3 over Japan in the anticyclonic conditions that favor regional O-3 buildup and are thus expected to have a small but significant effect on regional air quality. Finally, we demonstrate that location and transport lead to European sources having a different impact on OH, and hence on tropospheric oxidizing capacity and climate, from other major Northern Hemisphere source regions

Time -dependent effects in post -tensioned concrete -steel composite girder bridges

In continuous concrete-steel composite girder bridges, the concrete contribution to the composite action at interior supports is impaired because the concrete deck is in tension. Post-tensioning introduces compression to the structure and reinstates the contribution of concrete to the composite action. Janssen and Spaans (1994) proposed a post-tensioning scheme, which involved using concrete end diaphragms as anchorage and concrete intermediate diaphragms as draped points for steel tendons. In the short-term, this scheme produces structurally and economically efficient structures. Long-term efficiency, however, can only be assessed once the time dependent effects caused by creep, shrinkage, and relaxation are considered. In this study, finite element models were used to study the time dependent effects in post-tensioned composite girder bridges. How post-tensioning induced stresses, internal forces, and deflection change with time were investigated. Parametric studies were conducted to study how changes in these quantities were affected by bridge geometry, material properties and surrounding conditions. Finally, a simplified design approach to account for time dependent effects was proposed. It was found that time dependent effects in terms of change in stresses and internal forces are considerable. While shrinkage has the most profound effect in terms of prestress loss, creep plays a major role in terms of stress changes and moment redistribution. Change in deflection is small due to the cancellation effects of creep and shrinkage. Despite the time dependent change in the post-tensioning effect, substantial material saving can still be realized in this type of bridge. Post-tensioned composite girder bridges still represent structurally and economically efficient structures

A Quantifiable Model for Local Bond Stress-Slip Relationship under Generalized Excitations

An analytical model for local bond stress-slip relationship proposed in this paper was developed because of the need for a reliable bond stress-slip model to be used in predicting the bond behavior between steel bars and concrete in the well-confined zones of concrete structures under generalized excitations. Both experimental and analytical programs were carried out in this study to find out the influence of lug parameters on the shape of the monotonic bond stress-slip curve. The proposed analytical bond stress-slip model is based on a concept of the mechanical bond strength of the concrete key (concrete between steel lugs) which is a combination of strength and friction. All of the model\u27s parameters are related to the bar\u27s deformation pattern and can be quantified directly from the physical dimensions of the bar. A scaling factor was introduced in order to include the effect of concrete strength. A simple damage rule was derived based on the length of the undamaged portion of the concrete key and the developed friction. A hysteresis rule was developed based on the concept of reduced monotonic envelope. The model is successful in predicting both slip control and load control test results and for low and very high numbers of load cycles. The model is incomplete because it does not include a mode of failure that may occur if the lug depth to lug spacing ratio is relatively high. Both the experimental and analytical results show that bond strength under fatigue loading is very sensitive to the scale of the deformation pattern, that is a small increase in scale factor of the deformation pattern has a large increase in fatigue resistance. The results also show that bond stiffness is roughly independent of the scale of the deformation pattern. However, if the scale of the deformation pattern is small enough, bond resistance in terms of the bond stress at failure will decrease even under monotonic loading and the mode of bond failure will change from mechanical bearing to adhesion and friction