Technical note: a new method for the Lagrangian tracking of pollution plumes from source to receptor using gridded model output

Lagrangian particle dispersion models (LPDMs) are powerful and popular tools used for the analysis of atmospheric trace gas measurements. However, it can be difficult to determine the transport pathway of emissions from their source to a receptor using the standard gridded model output, particularly during complex meteorological scenarios. In this paper we present a method to clearly and easily identify the pathway taken by only those emissions that arrive at a receptor at a particular time, by combining the standard gridded output from forward (e.g., concentration) and backward (e.g., residence time) LPDM simulations. By comparing the pathway determined from this method with particle trajectories from both the forward and backward models, we show that this method successfully restores much of the Lagrangian information that is lost when the data are gridded. A sample analysis is presented, demonstrating that the sourceto-receptor pathway determined from this method is more accurate and easier to use than existing methods using standard LPDM products (gridded fields of, e.g., concentrations and residence time). As demonstrated in an evaluation and an example application, the method requires agreement between the transport described by the forward and backward simulations and thus provides a means to assess the quality and reversibility of the simulation. Finally, we discuss the potential for combining the backward LPDM simulation with gridded data from other sources (e.g., chemical transport models) to obtain a Lagrangian sampling of the air that will eventually arrive at a receptor. Based on the advantages presented here, this new method can complement or even replace many of the standard uses of backward LPDM simulations

Evaluation of active control technology for short haul aircraft

An evaluation of the economics of short-haul aircraft designed with active controls technology and low wing-loading to achieve short field performance with good ride quality is presented. Results indicate that for such a system incorporating gust load alleviation and augmented stability the direct operating cost is better than for aircraft without active controls

Release of NO(x) from sunlight-irradiated midlatitude snow

Photochemical production and release of gas-phase NO(x) (NO + NO2) from the natural snowpack at a remote site in northern Michigan were investigated during the Snow Nitrogen and Oxidants in Winter study in January 1999. Snow was collected in an open 34 L chamber, which was then sealed with a transparent Teflon cover and used as an outdoor flow and reaction chamber. Significant increases in NO(x) mixing ratio were observed in synthetic and ambient air pulled through the sunlit chamber. [NO(x)] enhancements were correlated to ultraviolet sunlight intensity, reaching ~300 pptv under partially overcast midday, mid-winter conditions. These findings are consistent with NO(x) production from photolysis of snowpack NO3 -; the observed NO(x) release implies production of significant amounts of OH within the snow. Snowpack NO3 - photolysis may therefore significantly alter boundary layer levels of both NO(x) and oxidized compounds over wide regions of the atmosphere

Multibody aircraft study, volume 2

The potential benefits of a multibody aircraft when compared to a single body aircraft are presented. The analyses consist principally of a detailed point design analysis of three multibody and one single body aircraft, based on a selected payload of 350,000 kg (771,618 lb), for final aircraft definitions; sensitivity studies to evaluate the effects of variations in payload, wing semispan body locations, and fuel price; recommendations as to the research and technology requirements needed to validate the multibody concept. Two, two body, one, three body, and one single body aircraft were finalized for the selected payload, with DOC being the prime figure of merit. When compared to the single body, the multibody aircraft showed a reduction in DOC by as much as 11.3 percent. Operating weight was reduced up to 14 percent, and fly away cost reductions ranged from 8.6 to 13.4 percent. Weight reduction, hence cost, of the multibody aircraft resulted primarily from the wing bending relief afforded by the bodies being located outboard on the wing

Significant enhancements of nitrogen oxides, black carbon, and ozone in the North Atlantic lower free troposphere resulting from North American boreal wildfires

Copyright © 2006 American Geophysical Union. All Rights Reserved.Extensive wildfires burned in northern North America during summer 2004, releasing large amounts of trace gases and aerosols into the atmosphere. Emissions from these wildfires frequently impacted the PICO-NARE station, a mountaintop site situated 6–15 days downwind from the fires in the Azores Islands. To assess the impacts of the boreal wildfire emissions on the levels of aerosol black carbon (BC), nitrogen oxides and O3 downwind from North America, we analyzed measurements of CO, BC, total reactive nitrogen oxides (NO y ), NO x (NO + NO2) and O3 made from June to September 2004 in combination with MOZART chemical transport model simulations. Long-range transport of boreal wildfire emissions resulted in large enhancements of CO, BC, NO y and NO x , with levels up to 250 ppbv, 665 ng mˉ³, 1100 pptv and 135 pptv, respectively. Enhancement ratios relative to CO were variable in the plumes sampled, most likely because of variations in wildfire emissions and removal processes during transport. Analyses of ΔBC/ΔCO, ΔNO y /ΔCO and ΔNO x /ΔCO ratios indicate that NO y and BC were on average efficiently exported in these plumes and suggest that decomposition of PAN to NO x was a significant source of NO x . High levels of NO x suggest continuing formation of O3 in these well-aged plumes. O3 levels were also significantly enhanced in the plumes, reaching up to 75 ppbv. Analysis of ΔO3/ΔCO ratios showed distinct behaviors of O3 in the plumes, which varied from significant to lower O3 production. We identify several potential reasons for the complex effects of boreal wildfire emissions on O3 and conclude that this behavior needs to be explored further in the future. These observations demonstrate that boreal wildfire emissions significantly contributed to the NO x and O3 budgets in the central North Atlantic lower free troposphere during summer 2004 and imply large-scale impacts on direct radiative forcing of the atmosphere and on tropospheric NO x and O3

Late summer changes in burning conditions in the boreal regions and their implications for NO x and CO emissions from boreal fires

Copyright © 2008 American Geophysical Union. All Rights Reserved.Building emission inventories for the fires in boreal regions remains a challenging task with significant uncertainties in the methods used. In this work, we assess the impact of seasonal trends in fuel consumption and flaming/smoldering ratios on emissions of species dominated by flaming combustion (e.g., NO x ) and species dominated by smoldering combustion (e.g., CO). This is accomplished using measurements of CO and NO y at the free tropospheric Pico Mountain observatory in the central North Atlantic during the active boreal fire seasons of 2004 and 2005. ΔNO y /ΔCO enhancement ratios in aged fire plumes had higher values in June-July (7.3 × 10−3 mol mol−1) relative to the values in August-September (2.8 × 10−3 mol mol−1), indicating that NO x /CO emission ratios declined significantly as the fire season progressed. This is consistent with our understanding that an increased amount of fuel is consumed via smoldering combustion during late summer, as deeper burning of the drying organic soil layer occurs. A major growth in fuel consumption per unit area is also expected, due to deeper burning. Emissions of CO and NO x from North American boreal fires were estimated using the Boreal Wildland Fire Emissions Model, and their long-range transport to the sampling site was modeled using FLEXPART. These simulations were generally consistent with the observations, but the modeled seasonal decline in the ΔNO y /ΔCO enhancement ratio was less than observed. Comparisons using alternative fire emission injection height scenarios suggest that plumes with the highest CO levels at the observatory were lofted well above the boundary layer, likely as a result of intense crown fires

Free-troposphere ozone and carbon monoxide over the North Atlantic for 2001-2011

In situ measurements of carbon monoxide (CO) and ozone (O3) at the Pico Mountain Observatory (PMO) located in the Azores, Portugal, are analyzed together with results from an atmospheric chemical transport model (GEOS-Chem) and satellite remote sensing data (AIRS (Atmospheric Infrared Sounder) for CO, and TES (Tropospheric Emission Spectrometer) for O3) to examine the evolution of free-troposphere CO and O3 over the North Atlantic for 2001-2011. GEOS-Chem captured the seasonal cycles for CO and O3 well but significantly underestimated the mixing ratios of CO, particularly in spring. Statistically significant (using a significance level of 0.05) decreasing trends were found for both CO and O3 based on harmonic regression analysis of the measurement data. The best estimates of the possible trends for CO and O3 measurements are -0.31 ± 0.30 (2-σ) ppbv yr-1 and -0.21 ± 0.11 (2-σ) ppbv yr-1, respectively. Similar decreasing trends for both species were obtained with GEOS-Chem simulation results. The most important factor contributing to the decreases in CO and O3 at PMO over the past decade is the decline in anthropogenic emissions from North America, which more than compensate for the impacts from increasing Asian emissions. It is likely that climate change in the past decade has also affected the intercontinental transport of O3

A semi-Lagrangian view of ozone production tendency in North American outflow in the summers of 2009 and 2010

The Pico Mountain Observatory, located at 2225 m a.s.l. in the Azores Islands, was established in 2001 to observe long-range transport from North America to the central North Atlantic. In previous research conducted at the observatory, ozone enhancement (\u3e 55 ppbv) in North American outflows was observed, and efficient ozone production in these outflows was postulated. This study is focused on determining the causes for high d[O3] / d[CO] values (~1 ppbv ppbv−1) observed in the summers of 2009 and 2010. The folded retroplume technique, developed by Owen and Honrath (2009), was applied to combine upwind FLEXPART transport pathways with GEOS-Chem chemical fields. The folded result provides a semi-Lagrangian view of polluted North American outflow in terms of physical properties and chemical processes, including production/loss rate of ozone and NOx produced by lightning and thermal decomposition of peroxy acetyl nitrate (PAN). Two transport events from North America were identified for detailed analysis. High d[O3] / d[CO] was observed in both events, but due to differing transport mechanisms, ozone production tendency differed between the two. A layer of net ozone production was found at 2 km a.s.l. over the Azores in the first event plume, apparently driven by PAN decomposition during subsidence of air mass in the Azores–Bermuda High. In the second event, net ozone loss occurred during transport in the lower free troposphere, yet observed d[O3] / d[CO] was high. We estimate that in both events, CO loss through oxidation contributed significantly to d[O3] / d[CO] enhancement. Thus, it is not appropriate to use CO as a passive tracer of pollution in these events. In general, use of d[O3] / d[CO] as an indicator of net ozone production/loss may be invalid for any situation in which oxidants are elevated. Based on our analysis, use of d[O3] / d[CO] to diagnose ozone enhancement without verifying the assumption of negligible CO loss is not advisable

Power-Based Droop Control in DC Microgrids Enabling Seamless Disconnection From Upstream Grids

This paper proposes a local power-based droop controller for distributed energy resource converters in dc microgrids that are connected to upstream grids by grid-interface converters. During normal operation, the grid-interface converter imposes the microgrid bus voltage, and the proposed controller allows power flow regulation at distributed energy resource converters\u2019 output. On the other hand, during abnormal operation of the grid-interface converter (e.g., due to faults in the upstream grid), the proposed controller allows bus voltage regulation by droop control. Notably, the controller can autonomously convert from power flow control to droop control, without any need of bus voltage variation detection schemes or communication with other microgrid components, which enables seamless transitions between these two modes of operation. Considering distributed energy resource converters employing the power-based droop control, the operation modes of a single converter and of the whole microgrid are defined and investigated herein. The controller design is also introduced. Furthermore, the power sharing performance of this control approach is analyzed and compared with that of classical droop control. The experimental results from a laboratory-scale dc microgrid prototype are reported to show the final performances of the proposed power-based droop control

Regional and hemispheric impacts of anthropogenic and biomass burning emissions on summertime CO and O3 in the North Atlantic lower free troposphere

Copyright © 2004 American Geophysical Union. All Rights Reserved.We report summertime measurements of CO and O3 obtained during 2001–2003 at the PICO-NARE mountaintop station in the Azores. Frequent events of elevated CO mixing ratios were observed. On the basis of backward trajectories arriving in the free troposphere and global simulations of biomass burning plumes, we attribute nearly all these events to North American pollution outflow and long-range transport of biomass burning emissions. There was a high degree of interannual variability in CO levels: median [CO] ranged from 65 ppbv in 2001 to 104 ppbv in 2003. The highest concentrations were associated with transport of Siberian fire emissions during summer 2003, when Siberian fire activity was unusually high. Ozone mixing ratios also increased (by up to ∼30 ppbv) during the fire events. These findings demonstrate the significant hemispheric scale impact that biomass burning events have on background CO and O3 levels. O3 enhancements of similar magnitude were also observed in North American pollution outflow. O3 and CO were correlated during North American outflow events, with a slope averaging 1.0 (d[O3]/d[CO], ppbv/ppbv) when no fire impact was present. This slope is more than 80% larger than early 1990s observations made in the eastern United States and nearshore outflow region, even after accounting for declining U.S. CO emissions and for CO loss during transport to the Azores, and is not consistent with simple dilution of U.S. outflow with marine background air. We conclude that a significantly larger amount of O3 production occurred in the air sampled during this study, and we suggest several potential reasons for this, each of which could imply potentially significant shortcomings in current estimates of the hemispheric impact of North American emissions on tropospheric ozone and should be evaluated in future studies