Papers by Robert B Chatfield
This is a good basic publication which just needs clarity and precision. Conclusions regarding tr... more This is a good basic publication which just needs clarity and precision. Conclusions regarding trends in retrieved ozone need more modest standard error estimates, I believe
Previous studies of emission factors from biomass burning are prone to large errors since they ig... more Previous studies of emission factors from biomass burning are prone to large errors since they ignore the interplay of mixing and varying pre-fire background CO2 levels. Such complications severely affected our studies of 446 forest fire plume samples measured in the Western US by the science teams of NASA's SEAC4RS and ARCTAS airborne missions. Consequently we propose a Mixed Effects Regression Emission Technique (MERET) to check techniques like the Normalized Emission Ratio Method (NERM), where use of sequential observations cannot disentangle emissions and mixing. We also evaluate a simpler "consensus" technique. All techniques relate emissions to fuel burned using Cburn = ΔCtot added to the fire plume, where Ctot ≈ (CO2 + CO). Mixed-effects regression can estimate pre-fire background values of Ctot (indexed by observation j) simultaneously with emissions factors indexed by individual species i, δελτα−xi /(Cburn)i,j., MERET and "consensus" require more than two emissions indicators. Our studies excluded samples where exogenous CO or CH4 might have been fed into a fire plume, mimicking emission. We sought to let the data on 13 gases and particulate properties suggest clusters of variables and plume types, using non-negative matrix factorization (NMF). While samples were mixtures, the NMF unmixing suggested purer burn types. Particulate properties (bscat, babs, SSA, AÅE) and gas-phase emissions were interrelated. Finally, we sought a simple categorization useful for modeling ozone production in plumes. Two kinds of fires produced high ozone: those with large fuel nitrogen as evidenced by remnant CH3CN in the plumes, and also those from very intense large burns. Fire types with optimal ratios of delta-NOy/delta-HCHO associate with the highest additional ozone per unit Cburn, Perhaps these plumes exhibit limited NOx binding to reactive organics. Perhaps these plumes exhibit limited NOx binding to reactive organics.
AGU Fall Meeting Abstracts, Dec 1, 2018
Integrated quantitative gas chromatographic measurements of the nearly one hundred individual hyd... more Integrated quantitative gas chromatographic measurements of the nearly one hundred individual hydrocarbons present in ambient air were made to deternime the total non-methane organic burden at a midwest rural site in coordination with halocarbon, oxidant and local meteorological variables in July and August 1975. Although the sample location was clearly rural, it was only 100 km north of St. Louis, Missouri. Consequently, four situations could be distinguished at this site: clean rural air, transport from near urban areas, transport from distant urban areas, and air-mass stagnation. In the later situation, the rural air was well mixed on a regional scale with natural and anthropogenic ozone precursors. Fluorocarbon-11 and meteorological data were used to identify and describe the four situations and to interpret the observed concentrations of hydrocarbons and oxidant resulting from local photochemistry and transport.
Remote Sensing of Environment, 2015
We may have considerable optimism that concentrations of pollutants retrievable from space are qu... more We may have considerable optimism that concentrations of pollutants retrievable from space are quite relevant in mapping near-surface O3 smog pollution. A general relationship obtains between O3 in near-surface layers - important for air pollution exposure assessment - and ozone in a deeper region of the troposphere - the thinnest layer to be retrieved potentially by remote sensing. This relationship has been observed where plentiful measurements of North American ozonesonde network. [Chatfield ..., AE, 2011]. Does it hold for complex urbanized and industrial regions? Does it hold for O3 precursors and for the O3 chemical production rate P(O3)? The answers determine the usefulness of proposed missions like NASA's GEO-CAPE geostationary observations. The DISCOVER-AQ airborne study repeatedly made spirals over various urban, industrial, transportation, and rural sites in detail around the Baltimore-Washington area in July, 2011. We compare mixing ratios appropriately averaged over...
SPIE Proceedings, 2005
Precise measurements of CH4 in a column of near surface air, and in partial columns above this, w... more Precise measurements of CH4 in a column of near surface air, and in partial columns above this, would be very valuable in identifying sources/sinks of atmospheric CH4, and its transport. For this purpose we have proposed a grating mapping spectrometer (GMS) for deployment as an Instrument of Opportunity (IOO) on the NPOESS that acquires data in the 2990 to 3050
Geophysical Research Letters, 1985
Recent measurements of tropospheric mixing ratios of methane, non-methane hydrocarbons (NMHC), an... more Recent measurements of tropospheric mixing ratios of methane, non-methane hydrocarbons (NMHC), and carbon monoxide (CO)from the Kenyan savannah are reported. NMHC mixing ratios are among the lowest reported for the continental boundary layer. CO mixing ratios are higher than marine measurements at these latitudes. Biomass burning may contribute significantly to mixing ratios of CO and NMHC's. Calculations based on the reactivity of the OH radical with NMHC's and CO indicate that NMHC's often initially consume more OH than CO. Experimental Techniques Sample collection procedures and analytical techniques employed for NMHC's are described in Greenberg and Zimmerman [1984]. Air samples were collected on the ground and pressurized in evacuated, elec
There is significant controversy on whether extratropical fires contribute importantly to widespr... more There is significant controversy on whether extratropical fires contribute importantly to widespread ozone production absent the addition of urban pollutant nitrogen oxides (Jaffe and Widger, 2012, Singh et al., 2012,2013). We report a significant range of O 3 production early in the fire plume history and report controls on which notable O 3 production occurs. The current data set is the airborne observations made on board NASA's highly instrumented DC-8 aircraft during the ARCTAS (2008) and SEAC4RS (2013) campaigns within the Western United States. A clear analysis of fire emissions was aided considerably by MERET (a Mixed Effects Regressions Emissions Technique). This technique allows consistent emission factors and enhancement ratios for O 3 for individual aircraft samples largely free from uncertainties resulting from mixing and entrainment which plague many published estimates. (Yokelson et al, 2013, Chatfield and Andreae, 2016). We find support for the reasonable idea that the ratio of nitrogen oxides (NO x) to volatile organic carbon (VOC) emissions controls new O 3 production. The evidence is for significant O 3 production from high-fuel-nitrogen fuels (as evidenced by acetonitrile) and extremely hot large fires (like the Yosemite Rim Fire of 2013 which we analyze), while others do not. VOC emissions factors vary significantly from fire to fire (and from different samples in the Rim Fire). Relative CO production (aka "modified combustion efficiency") is only one factor describing VOC emissions factors.
Burning to clear land for crops and to destroy pests is an integral and largely unavoidable part ... more Burning to clear land for crops and to destroy pests is an integral and largely unavoidable part of tropical agriculture. It is easy to note but difficult to quantify using remote sensing. This report describes our efforts to integrate remotely sensed data into our computer model of tropical chemical trace-gas emissions, weather, and reaction chemistry (using the MM5 mesoscale model and our own Global-Regional Atmospheric Chemistry Simulator). The effects of burning over the continents of Africa and South America have been noticed in observations from several satellites. Smoke plumes hundreds of kilometers long may be seen individually, or may merge into a large smoke pall over thousands of kilometers of these continents. These features are related to intense pollution in the much more confined regions with heavy burning. These emissions also translocate nitrogen thousands of kilometers in the tropical ecosystems, with large fixed-nitrogen losses balanced partially by locally intens...
Journal of Geophysical Research: Atmospheres, 1998
The “Great African Plume” flows westward from a wind divergence line over Central Africa to pollu... more The “Great African Plume” flows westward from a wind divergence line over Central Africa to pollute the Equatorial Atlantic Ocean. The plume arises from agricultural burning fumes which mix in a 3–4 km deep boundary layer over Africa, then override cooler rainforest air, and finally swerve westward, where their progress into the Atlantic is “gated” by southern storm systems. Another prominent elevated “Global Burning Plume” from Tropical South America flows past South Africa above 8 km altitude. Joining elevated African plumes, it influences the South Indian and Southern Oceans. These are results from our GRACES (Global Regional Atmospheric Chemistry Event Simulator), which was used to study carbon monoxide during an intensive experimental period, September‐October 1992. Traces of the plumes are also evident in observations of CO in the Measurement of Air Pollution from Satellites (MAPS) samples of October, 1994, suggesting a general phenomena. To arrive at these conclusions, we use...
Particulate air quality monitoring is traditionally done by point surface measurements. Satellite... more Particulate air quality monitoring is traditionally done by point surface measurements. Satellite measurements of aerosol properties have the potential to augment surface measurements. They can provide better spatial coverage to see pollutant levels in remote and non-monitored areas, track pollution transport, validate and guide models prediction, suggest the placement of future surface sensors, and provide another metric in epidemiological studies. The problem in implementation is that correlations between surface PM2.5 measurements and satellite aerosol optical depth measurements show a great deal of variation, between 0.2 and 0.98 depending on the season and location or region of comparison. In some cases, notably in the western US, there is little or no correlation (1, 2) using simple linear regression to match AOD to PM. Our group at NASA Ames has developed methods to improve these correlations by employing generalized additive models (GAMs). Our methodology is also unique beca...
Biomass burning is a common human activity in much of the developing tropical world where it has ... more Biomass burning is a common human activity in much of the developing tropical world where it has wide-ranging environmental impacts. Fire, a large component of tropical deforestation, is often used to clear broad expanses of land for shifting agriculture and cattle ranching. Frequent burning in the tropical savannas creates problems distinct from those of burning in the primary forest. In Brazil, much of the burning occurs in the Cerrado, which occupies approximately 1.800.000 km2, primarily on the great plateau in Central Brazil. Wildland and agricultural fires are sources of regional air pollution in Central Brazil, and release a large number of trace gases, including greenhouse and other chemically active species. Knowledge of trace gas emissions from biomass burning in Brasil, however, is limited by a number of factors, most notably lack of relative emission factors for gases from specific fire types/fuels and accurate estimates of temporal and spatial distribution and extent of...
Air quality agencies use ground sites to monitor air quality, providing accurate information at p... more Air quality agencies use ground sites to monitor air quality, providing accurate information at particular points. Using measurements from satellite imagery has the potential to provide air quality information in a timely manner with better spatial resolution and at a lower cost that can also useful for model validation. While previous studies show acceptable correlations between Aerosol Optical Depth (AOD)
Remote Sensing of Environment, 2019
The Multiangle Implementation of Atmospheric Correction (MAIAC) is a new generic algorithm applie... more The Multiangle Implementation of Atmospheric Correction (MAIAC) is a new generic algorithm applied to collection 6 (C6) MODIS measurements to retrieve Aerosol Optical Depth (AOD) over land at high spatial resolution (1 km). This study is the first evaluation of the MAIAC AOD from MODIS Aqua (A) and Terra (T) satellites between 2006 and 2016 over South Asia. The retrieval accuracy of MAIAC was assessed by comparing it to ground-truth AErosol RObotic NETwork (AERONET) AOD, as well as to AOD retrieved by the two operational MODIS algorithms: Dark Target (DT) and Deep Blue (DB). MAIAC AOD showed higher spatial coverage and retrieval frequency than either the DT or the DB AOD retrievals. The high spatial resolution of the MAIAC retrievals enhances the capability to distinguish aerosol sources and to determine fine aerosol features, such as wildfire smoke plumes and haze over complex geographical regions, and provides more retrievals in conditions that are cloudy or when the surface is partially covered by snow. In comparison to AERONET AOD, MAIAC AOD shows a better accuracy than both DT and DB AOD. A higher number of MAIAC-AERONET AOD matchups demonstrate the capability of MAIAC to retrieve AOD over varied surfaces, different aerosol types and loadings. Our results demonstrate high retrieval accuracy in term of the Expected Error (EE)
Atmospheric Chemistry and Physics Discussions, 2015
In order to utilize satellite-based aerosol measurements for the determination of air quality, th... more In order to utilize satellite-based aerosol measurements for the determination of air quality, the relationship between aerosol optical properties (wavelength-dependent, column-integrated extinction measured by satellites) and mass measurements of aerosol loading (PM<sub>2.5</sub> used for air quality monitoring) must be understood. This connection varies with many factors including those specific to the aerosol type, such as composition, size and hygroscopicity, and to the surrounding atmosphere, such as temperature, relative humidity (RH) and altitude, all of which can vary spatially and temporally. During the DISCOVER-AQ (Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality) project, extensive in-situ atmospheric profiling in the Baltimore, MD–Washington, DC region was performed during fourteen flights in July 2011. Identical flight plans and profile locations throughout the project provide meaningful stat...
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Papers by Robert B Chatfield