Implementation of a Markov Chain Monte Carlo method to inorganic aerosol modeling of observations from the MCMA-2003 campaign ? Part I: Model description and application to the La Merced site

International audienceThe equilibrium inorganic aerosol model ISORROPIA was embedded in a Markov Chain Monte Carlo algorithm to develop a powerful tool to analyze aerosol data and predict gas phase concentrations where these are unavailable. The method directly incorporates measurement uncertainty, prior knowledge, and provides a formal framework to combine measurements of different quality. The method was applied to particle- and gas-phase precursor observations taken at La Merced during the Mexico City Metropolitan Area (MCMA) 2003 Field Campaign and served to discriminate between diverging gas-phase observations of ammonia and predict gas-phase concentrations of hydrochloric acid. The model reproduced observations of particle-phase ammonium, nitrate, and sulfate well. The most likely concentrations of ammonia were found to vary between 4 and 26 ppbv, while the range for nitric acid was 0.1 to 55 ppbv. During periods where the aerosol chloride observations were consistently above the detection limit, the model was able to reproduce the aerosol chloride observations well and predicted the most likely gas-phase hydrochloric acid concentration varied between 0.4 and 5 ppbv. Despite the high ammonia concentrations observed and predicted by the model, when the aerosols were assumed to be in the efflorescence branch they are predicted to be acidic (pH~3)

Implementation of a Markov Chain Monte Carlo method to inorganic aerosol modeling of observations from the MCMA-2003 campaign ? Part II: Model application to the CENICA, Pedregal and Santa Ana sites

International audienceA Markov Chain Monte Carlo model for integrating the observations of inorganic species with a thermodynamic equilibrium model was presented in Part I of this series. Using observations taken at three ground sites, i.e. a residential, industrial and rural site, during the MCMA-2003 campaign in Mexico City, the model is used to analyze the inorganic particle and ammonia data and to predict gas phase concentrations of nitric and hydrochloric acid. In general, the model is able to accurately predict the observed inorganic particle concentrations at all three sites. The agreement between the predicted and observed gas phase ammonia concentration is excellent. The NOz concentration calculated from the NOy, NO and NO2 observations is of limited use in constraining the gas phase nitric acid concentration given the large uncertainties in this measure of nitric acid and additional reactive nitrogen species. Focusing on the acidic period of 9?11 April identified by Salcedo et al. (2006), the model accurately predicts the particle phase observations during this period with the exception of the nitrate predictions after 10:00 a.m. (Central Daylight Time, CDT) on 9 April, where the model underpredicts the observations by, on average, 20%. This period had a low planetary boundary layer, very high particle concentrations, and higher than expected nitrogen dioxide concentrations. For periods when the particle chloride observations are consistently above the detection limit, the model is able to both accurately predict the particle chloride mass concentrations and provide well-constrained HCl (g) concentrations. The availability of gas-phase ammonia observations helps constrain the predicted HCl (g) concentrations. When the particles are aqueous, the most likely concentrations of HCl (g) are in the sub-ppbv range. The most likely predicted concentration of HCl (g) was found to reach concentrations of order 10 ppbv if the particles are dry. Finally, the atmospheric relevance of HCl (g) is discussed in terms of its indicator properties for the possible influence of chlorine-mediated photochemistry in Mexico City

Soil gas probes for monitoring trace gas messengers of microbial activity

Soil microbes vigorously produce and consume gases that reflect active soil biogeochemical processes. Soil gas measurements are therefore a powerful tool to monitor microbial activity. Yet, the majority of soil gases lack non-disruptive subsurface measurement methods at spatiotemporal scales relevant to microbial processes and soil structure. To address this need, we developed a soil gas sampling system that uses novel diffusive soil probes and sample transfer approaches for high-resolution sampling from discrete subsurface regions. Probe sampling requires transferring soil gas samples to above-ground gas analyzers where concentrations and isotopologues are measured. Obtaining representative soil gas samples has historically required balancing disruption to soil gas composition with measurement frequency and analyzer volume demand. These considerations have limited attempts to quantify trace gas spatial concentration gradients and heterogeneity at scales relevant to the soil microbiome. Here, we describe our new flexible diffusive probe sampling system integrated with a modified, reduced volume trace gas analyzer and demonstrate its application for subsurface monitoring of biogeochemical cycling of nitrous oxide (N2O) and its site-specific isotopologues, methane, carbon dioxide, and nitric oxide in controlled soil columns. The sampling system observed reproducible responses of soil gas concentrations to manipulations of soil nutrients and redox state, providing a new window into the microbial response to these key environmental forcings. Using site-specific N2O isotopologues as indicators of microbial processes, we constrain the dynamics of in situ microbial activity. Unlocking trace gas messengers of microbial activity will complement -omics approaches, challenge subsurface models, and improve understanding of soil heterogeneity to disentangle interactive processes in the subsurface biome. © 2021, The Author(s).Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Characterization of on-road vehicle emissions in the Mexico City Metropolitan Area using a mobile laboratory in chase and fleet average measurement modes during the MCMA-2003 field campaign

International audienceA mobile laboratory was used to measure on-road vehicle emission ratios during the MCMA-2003 field campaign held during the spring of 2003 in the Mexico City Metropolitan Area (MCMA). The measured emission ratios represent a sample of emissions of in-use vehicles under real world driving conditions for the MCMA. From the relative amounts of NOx and selected VOC's sampled, the results indicate that the technique is capable of differentiating among vehicle categories and fuel type in real world driving conditions. Emission ratios for NOx, NOy, NH3, H2CO, CH3CHO, and other selected volatile organic compounds (VOCs) are presented for chase sampled vehicles in the form of frequency distributions as well as estimates for the fleet averaged emissions. Our measurements of emission ratios for both CNG and gasoline powered "colectivos" (public transportation buses that are intensively used in the MCMA) indicate that ? in a mole per mole basis ? have significantly larger NOx and aldehydes emissions ratios as compared to other sampled vehicles in the MCMA. Similarly, ratios of selected VOCs and NOy showed a strong dependence on traffic mode. These results are compared with the vehicle emissions inventory for the MCMA, other vehicle emissions measurements in the MCMA, and measurements of on-road emissions in U.S. cities. We estimate NOx emissions as 100 600±29 200 metric tons per year for light duty gasoline vehicles in the MCMA for 2003. According to these results, annual NOx emissions estimated in the emissions inventory for this category are within the range of our estimated NOx annual emissions. Our estimates for motor vehicle emissions of benzene, toluene, formaldehyde, and acetaldehyde in the MCMA indicate these species are present in concentrations higher than previously reported. The high motor vehicle aldehyde emissions may have an impact on the photochemistry of urban areas

Versatile soil gas concentration and isotope monitoring: Optimization and integration of novel soil gas probes with online trace gas detection

Gas concentrations and isotopic signatures can unveil microbial metabolisms and their responses to environmental changes in soil. Currently, few methods measure in situ soil trace gases such as the products of nitrogen and carbon cycling or volatile organic compounds (VOCs) that constrain microbial biochemical processes like nitrification, methanogenesis, respiration, and microbial communication. Versatile trace gas sampling systems that integrate soil probes with sensitive trace gas analyzers could fill this gap with in situ soil gas measurements that resolve spatial (centimeters) and temporal (minutes) patterns. We developed a system that integrates new porous and hydrophobic sintered polytetrafluoroethylene (sPTFE) diffusive soil gas probes that non-disruptively collect soil gas samples with a transfer system to direct gas from multiple probes to one or more central gas analyzer(s) such as laser and mass spectrometers. Here, we demonstrate the feasibility and versatility of this automated multiprobe system for soil gas measurements of isotopic ratios of nitrous oxide (δ18O, δ15N, and the 15N site preference of N2O), methane, carbon dioxide (δ13C), and VOCs. First, we used an inert silica matrix to challenge probe measurements under controlled gas conditions. By changing and controlling system flow parameters, including the probe flow rate, we optimized recovery of representative soil gas samples while reducing sampling artifacts on subsurface concentrations. Second, we used this system to provide a real-time window into the impact of environmental manipulation of irrigation and soil redox conditions on in situ N2O and VOC concentrations. Moreover, to reveal the dynamics in the stable isotope ratios of N2O (i.e., 14N14N16O, 14N15N16O, 15N14N16O, and 14N14N18O), we developed a new high-precision laser spectrometer with a reduced sample volume demand. Our integrated system - a tunable infrared laser direct absorption spectrometry (TILDAS) in parallel with Vocus proton transfer reaction mass spectrometry (PTR-MS), in line with sPTFE soil gas probes - successfully quantified isotopic signatures for N2O, CO2, and VOCs in real time as responses to changes in the dry-wetting cycle and redox conditions. Broadening the collection of trace gases that can be monitored in the subsurface is critical for monitoring biogeochemical cycles, ecosystem health, and management practices at scales relevant to the soil system. © 2022 Juliana Gil-Loaiza et al.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Methane emission measurements in urban areas in eastern Germany

We have investigated methane emissions from urban sources in the former East Germany using innovative measurement techniques including a mobile real-time methane instrument and tracer release experiments. Anthropogenic and biogenic sources were studied with the emphasis on methane emissions from gas system sources, including urban distribution facilities and a production plant. Methane fluxes from pressure regulating stations ranged from 0.006 to 24. l/min. Emissions from diffuse sources in urban areas were also measured with concentration maps and whole city flux experiments. The area fluxes of the two towns studied were 0.37 and 1.9 g/m2/s. The emissions from individual gas system stations and total town emissions of this study are comparable to results of similar sites examined in the United States

Patterns of diversity in fatty-acid composition in the Australian groundnut germplasm collection

Knowledge of the amounts and types of fatty acids in groundnut oil is beneficial, particularly from a nutritional standpoint. Germplasm evaluation data for fatty acid composition on 819 accessions of groundnut (Arachis hypogaea L.) from the Australian Tropical Field Crops Genetic Resource Centre, Biloela, Queensland were examined. Data for eight quantitative fatty acid descriptors have been documented. Statistical assessment, via methods of pattern analysis, summarised and described the patterns of variation in fatty acid composition of the groundnut accessions in the Australian germplasm collection. Presentation of the results from principal components analysis and hierarchical cluster analysis using a biplot was shown to be a very useful interpretative tool. Such a biplot enables a simultaneous examination of the relationships among all the accessions and the fatty acids. Unlike that information available via database searches, the results from contribution analysis together with the biplot provide a global picture of the diversity available for use in plant breeding programs. The use of standardised data for eight fatty acids, compared to using three specific fatty acids, provided a better description of the total diversity available because it remains relevant with possible changes in the nutritional preferences for fatty acids. Fatty acid composition was found to vary in relation to the branching pattern of the accessions. This pattern is generally indicative of the botanical types of groundnuts; Virginia (alternate) compared to Spanish and Valencia (sequential) botanical types

Measurements and Analyses of Urban Metabolism and Trace Gas Respiration

Final Report on NASA ARI Contract No. 10066.Human society has well defined metabolic processes that can be characterized and quantified in the same way that an ecosystem’s metabolism can be defined and understood [Fischer-Kowalski, 1998.] The study of “industrial metabolism” is now a well-established topic, forming a key component of the emerging field of industrial ecology [Ayres and Simmonis, 1994; Fischer-Kowalski and Hüttler, 1998]. The fact that the metabolism of cities can be analyzed in a manner similar to that used for ecosystems or industries has long been recognized [Wolman, 1965.] However, the increasingly rapid pace of urbanization and the emergence of megacities, particularly in the developing world, lends increased urgency to the study of “urban metabolism.” A recent review by Decker et al. [2000] surveys energy and materials flow though the world’s twenty-five largest metropolitan areas. In 1995 these cities had populations estimated to range between 6.6 and 26.8 million people; all are expected to exceed 10 million by 2010. Urban metabolism, driven by the consumption of energy and materials, cannot take place without respiration. Both combustion based energy sources and the human and animal populations of cities consume atmospheric oxygen and expire carbon dioxide as well as a range of other trace gases and small particles. While the detail content of these urban emissions are generally not well known, there is no doubt that they are large and varied [Decker et al., 2000.] There is growing recognition that airborne emissions from major urban and industrial areas influence both air quality and climate change on scales ranging from regional up to continental and global. Urban/industrial emissions from the developed world, and increasingly from the megacities of the developing world change the chemical content of the downwind troposphere in a number of fundamental ways. Emissions of nitrogen oxides (NOx), CO and volatile organic compounds (VOCs) drive the formation of photochemical smog and its associated oxidants, degrading air quality and threatening both human and ecosystem health. On a larger scale, these same emissions drive the production of ozone (a powerful greenhouse gas) in the free troposphere, contributing significantly to global warming. Urban and industrial areas are also large sources of the major directly forcing greenhouse gases, including CO2, CH4, N2O and halocarbons. Nitrogen oxide and sulfur oxide emissions are also processed to strong acids by atmospheric photochemistry on regional to continental scales, driving acid deposition to sensitive ecosystems. Direct urban/industrial emission of carbonaceous aerosols is compounded by the emission of copious amounts of secondary aerosol precursors, including: NOx, VOCs, SO2, and NH3. The resulting mix of primary (directly emitted) and secondary aerosols is now recognized to play an important role in the climate of the Northern Hemisphere. What is less widely recognized is the poor state of our knowledge of the magnitudes, and spatial and temporal distributions, of gaseous and aerosol pollutants from urban/industrial areas. While most cities in the developed world do have a few continuous fixed site monitoring stations measuring point concentrations of regulated air pollutants; these measurements very poorly constrain the patterns of pollutant measurements from the urban area as a whole. Most cities in the developing world lack even these relatively sparse routine measurements. Air quality agencies in the developed world have assembled urban/industrial emissions inventories for some key pollutants, most notably NOx, CO, some VOCs, SO2, and some primary aerosols such as soot and particulate lead. However, far too often these emission inventories are based on engineering estimates rather than measured emissions. In addition, they often miss or poorly quantify smaller fixed sources, mobile sources (motor vehicles, trains, boats, aircraft) and area sources like landfills. Emissions inventories in developing countries, where they exist, are often based on dubious extrapolations of those used for cities in the developed world. This sad state of affairs is a serious problem. First, it is difficult to predict the impact of poorly defined emissions and pollutant distributions on urban air quality and its impact on citizen’s health and local ecosystem viability. Second, since the atmospheric chemistry which drives processes like ozone or secondary aerosol production is highly nonlinear, the impact of urban/industrial emissions on larger scales cannot be predicted without a relatively accurate and detailed knowledge of the temporal and spatial distributions of their precursors. Since “business as usual” is doing a poor job of specifying the real distributions of urban/ industrial atmospheric pollutants, new tools and techniques need to be developed to more easily and accurately quantify these emissions and allow accurate prediction of their subsequent chemical transformations and transport to larger scales. Our NASA Earth Science Enterprise funded Urban Metabolism and Trace Gas Respiration Project is an effort to better understand the distribution and emission patterns of pollutants in urban areas. The project took place between February, 1997 and October, 2001 as an Interdisciplinary Science (IDS) investigation associated with the Earth Observing System (EOS) project. It involved a highly interdisciplinary collaboration between five research teams from the Center for Atmospheric and Environmental Chemistry at Aerodyne Research, Inc. (ARI), the Departments of Chemical Engineering and Urban Studies and Planning at the Massachusetts Institute of Technology (MIT), the Institute of Earth, Oceans, and Space at the University of New Hampshire (UNH), and the Laboratory for Atmospheric Research at Washington State University (WSU). The team included physicists, physical chemists, and environmental engineers expert in atmospheric measurement techniques, chemical and environmental engineers skilled in developing and utilizing models of atmospheric chemistry and dynamics, and urban planners with a research focus on the development of geographical information systems (GIS) and their innovative use in mapping and intercomparing urban characteristics, including pollutant distributions. Graduate students from MIT, UNH, and WSU were involved in both the measurement and modeling/analyses portions of the project. Airborne platforms featuring fast response sensors have previously been deployed, with dramatic effect, to measure stratospheric and free tropospheric processes (e.g. Anderson et al., 1989) and even to follow urban emission plumes to quantify downwind pollution evolution [Trainor et al., 1995; Nunnermacker et al., 1998]. Components of our team have also used ground vehicles equipped with fast response trace gas sensors to quantify methane emissions from urban (and rural) components of natural and town gas systems, urban landfills, and sections of towns and cities [Lamb et al., 1995; Mosher et al, 1999; Shorter et al., 1996; 1997]. However, mobile fast response sensors had not been used previously to characterize multi-pollutant distributions and source emissions within urban areas. For this project we proposed to develop, deploy and demonstrate better urban atmospheric measurement techniques based on sensitive, accurate, real-time trace gas and particulate sensors onboard a ground mobile platform (a mobile laboratory.) We anticipated that the deployment of real-time (~1s response) sensitive and specific trace pollutant instruments in a mobile laboratory would generate a wealth of data on the distribution of both urban ambient pollutant levels and the distribution and nature of both mobile and stationary (including point and area) emission sources. As proposed, we first tested our instrumented mobile laboratory in two field missions in Manchester, NH a compact urban area with a population of ~100,000 well isolated from other urban centers. We then deployed our mobile laboratory in a intensive campaign in Boston, MA at the center of a metropolitan area with ~3 million people. These field programs allowed us to learn how to effectively deploy real-time mobile instruments in a major urban area and gain valuable data on pollutant distributions and emission sources. Our field measurement tools and strategies are presented in Section 2 of this report and an overview of the urban field measurement data we obtained is presented in Section 3. Since our real-time mobile measurements would generate copious amounts of data, a key programmatic goal was to develop the data reduction and analysis methods that would allow us to learn the most about pollutant distributions and emission sources. Further, since we proposed to develop novel methods of investigating urban gaseous polluant and fine particle emissions and distributions, we planned that analyses and evaluations of our initial field measurements would be used to design better measurement strategies to collect and analyze trace gas and fine particle concentration and flux data. In order to analyze experimental strategies and field measurement data the MIT and WSU groups have used state-of-the-art air quality models and developed new model analysis techniques. The WSU team developed a two component approach to model the turbulent atmospheric dynamics over urban landscapes. First, they used the Environmental Protection Agency’s (EPA’s) state-of-the-art MM5 model to provide a mesoscale model of the regional wind field and then applied TEMPEST, a 3-d turbulence model developed at the Pacific Northwest National Laboratory (PNNL) that simulates the actual urban landscape. WSU also developed a capability for predicting the downwind urban pollution footprint by combining MM5 computed windfields, MCIP, the meteorological processor from EPA’s Models-3/CMAQ model to invert the windfields, and the CALPUFF plume dispersion model. MIT used the MM5 windfields generated by WSU to test urban scale diffusion models by analyzing SF6 tracer release experiments performed as part of our Boston field campaign. In addition, the MM5 output was used to input the California Institute of Technology (CIT) air quality model to assist in analyses of the ozone and NOx trace gas distributions measured in Boston. Finally, MIT investigated the use of air quality model inversion techniques to determine how well spatial emissions distributions can be deduced from measured urban pollutant distributions. The project also involved the novel use of geographic information systems (GIS) and urban databases to correlate observed trace gas emission fluxes (urban respiration) with urban and industrial activity and consumption factors (urban metabolism). Finally, correlations between measured trace gas emissions and urban/industrial activity/ consumption factors are used to identify parameters accessible to air- and satellite-borne remote sensing systems in order to enable automated estimates of urban and industrial trace gas emissions relevant to global change and regional pollution issues.National Aeronautic and Space Administration