Spatial Variability of Trace Gases During DISCOVER-AQ: Planning for Geostationary Observations of Atmospheric Composition

Results from an in-depth analysis of trace gas variability in MD indicated that the variability in this region was large enough to be observable by a TEMPO-like instrument. The variability observed in MD is relatively similar to the other three campaigns with a few exceptions: CO variability in CA was much higher than in the other regions; HCHO variability in CA and CO was much lower; MD showed the lowest variability in NO2All model simulations do a reasonable job simulating O3 variability. For CO, the CACO simulations largely under over estimate the variability in the observations. The variability in HCHO is underestimated for every campaign. NO2 variability is slightly overestimated in MD, more so in CO. The TX simulation underestimates the variability in each trace gas. This is most likely due to missing emissions sources (C. Loughner, manuscript in preparation).Future Work: Where reasonable, we will use these model outputs to further explore the resolvability from space of these key trace gases using analyses of tropospheric column amounts relative to satellite precision requirements, similar to Follette-Cook et al. (2015)

An Elevated Reservoir of Air Pollutants over the Mid-Atlantic States During the 2011 DISCOVER-AQ Campaign: Airborne Measurements and Numerical Simulations

During a classic heat wave with record high temperatures and poor air quality from July 18 to 23, 2011, an elevated reservoir of air pollutants was observed over and downwind of Baltimore, MD, with relatively clean conditions near the surface. Aircraft and ozonesonde measurements detected approximately 120 parts per billion by volume ozone at 800 meters altitude, but approximately 80 parts per billion by volume ozone near the surface. High concentrations of other pollutants were also observed around the ozone peak: approximately 300 parts per billion by volume CO at 1200 meters, approximately 2 parts per billion by volume NO2 at 800 meters, approximately 5 parts per billion by volume SO2 at 600 meters, and strong aerosol optical scattering (2 x 10 (sup 4) per meter) at 600 meters. These results suggest that the elevated reservoir is a mixture of automobile exhaust (high concentrations of O3, CO, and NO2) and power plant emissions (high SO2 and aerosols). Back trajectory calculations show a local stagnation event before the formation of this elevated reservoir. Forward trajectories suggest an influence on downwind air quality, supported by surface ozone observations on the next day over the downwind PA, NJ and NY area. Meteorological observations from aircraft and ozonesondes show a dramatic veering of wind direction from south to north within the lowest 5000 meters, implying that the development of the elevated reservoir was caused in part by the Chesapeake Bay breeze. Based on in situ observations, Community Air Quality Multi-scale Model (CMAQ) forecast simulations with 12 kilometers resolution overestimated surface ozone concentrations and failed to predict this elevated reservoir; however, CMAQ research simulations with 4 kilometers and 1.33 kilometers resolution more successfully reproduced this event. These results show that high resolution is essential for resolving coastal effects and predicting air quality for cities near major bodies of water such as Baltimore on the Chesapeake Bay and downwind areas in the Northeast

Nitrogen dioxide and formaldehyde measurements from the GEOstationary Coastal and Air Pollution Events (GEO-CAPE) Airborne Simulator over Houston, Texas

The GEOstationary Coastal and Air Pollution Events (GEO-CAPE) Airborne Simulator (GCAS) was developed in support of NASA's decadal survey GEO-CAPE geostationary satellite mission. GCAS is an airborne push-broom remote-sensing instrument, consisting of two channels which make hyperspectral measurements in the ultraviolet/visible (optimized for air quality observations) and the visible–near infrared (optimized for ocean color observations). The GCAS instrument participated in its first intensive field campaign during the Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) campaign in Texas in September 2013. During this campaign, the instrument flew on a King Air B-200 aircraft during 21 flights on 11 days to make air quality observations over Houston, Texas. We present GCAS trace gas retrievals of nitrogen dioxide (NO2) and formaldehyde (CH2O), and compare these results with trace gas columns derived from coincident in situ profile measurements of NO2 and CH2O made by instruments on a P-3B aircraft, and with NO2 observations from ground-based Pandora spectrometers operating in direct-sun and scattered light modes. GCAS tropospheric column measurements correlate well spatially and temporally with columns estimated from the P-3B measurements for both NO2 (r2 = 0.89) and CH2O (r2 = 0.54) and with Pandora direct-sun (r2 = 0.85) and scattered light (r2 = 0.94) observed NO2 columns. Coincident GCAS columns agree in magnitude with NO2 and CH2O P-3B-observed columns to within 10&thinsp;% but are larger than scattered light Pandora tropospheric NO2 columns by 33&thinsp;% and direct-sun Pandora NO2 columns by 50&thinsp;%.</p

Properties of high-threshold mechanoreceptors in the oral mucosa. I. Responses to dynamic and static pressure

1. Mechanical response properties of high-threshold mechanoreceptors (HTMs) of the goat oral mucosa were determined by single-unit recording from the palatine and alveolar nerves and from the trigeminal ganglion. The following observations were made. 2. HTMs of the oral mucosa could be separated into two subgroups on the basis of their threshold to mechanical stimulation. Intense pressure receptors (IPRs) comprised a group of A-delta afferents with thresholds of 2-16 g. Mechanonociceptors (MNs) comprised a group of relatively slowly conducting afferents (A-delta and C-fibers) with a higher threshold range (16-300 g). 3. In most instances, MNs lacked pressure-transducing capacity. Tests of reactivity to dynamically or statically applied stimuli revealed that significant functions were rarely fit between MN activity and pressure (4/20 cases). 4. IPRs differed from MNs by their pressure-transducing properties. The afferent response interval was in inverse proportion to the applied pressure. Significant pressure interval functions were fit in 16/20 cases. The relationship between pressure and response interval was best described by power functions. 5. Tests of reactivity to dynamically or statically applied stimuli revealed that IPRs preferred static pressure. Tighter fits and steeper slopes were observed in power functions fit to data generated by statically applied stimuli (mean fitted function, dynamic test: LnISI = -0.97 LnP + 3.4; mean fitted function, static test: LnISI = -1.6 LnP + 4.71). 6. Pressures-frequency thresholds (PFTs), asymptotes (PFAs), and mean response intervals (MRIs) were determined for IPRs from the static test series. The first two values are the pressures that produce the lower and upper limits of response frequency of mucosal HTMs (mean PFT, 1.48 N/mm2; mean PFA, 3.34 N/mm2). The MRI (28 ms) is simply computed from the function. When PFTs and PFAs are combined with activation threshold and power functions, they provide a relatively complete description of the range and form of reactivity of the IPR of the oral mucosa. </jats:p

Errors in top-down estimates of emissions using a known source

Abstract. Air pollutant emissions estimates by top-down methods are subject to a variety of errors and uncertainties. This work uses a known source, a coal-fired power plant, to explore those errors. The known emissions amount and location remove two major types of error, facilitating understanding of other types. Biases and random errors are distinguished. A Lagrangian dispersion model (HYSPLIT) is run forward in time from the known source, and virtual measurements of the resulting tracer plume are compared to actual measurements from research aircraft. Four flights in different years are used to illustrate a variety of conditions. The measurements are analyzed by a mass-balance method, and the assumptions of that method are discussed. Some of those assumptions can be relaxed in analysis of the modeled plume, allowing testing of their validity. Meteorological fields to drive HYSPLIT are provided by the European Centre for Medium-Range Weather Forecasts Fifth Reanalysis (ERA5). A unique feature of this work is the use of an ensemble of meteorological fields intrinsic to ERA5. This analysis supports reasonably large (30 %–40 %) uncertainties on top-down analyses. </jats:p

Errors in top-down estimates of emissions using a known source

Abstract. Air pollutant emissions estimates by top-down methods are subject to a variety of errors and uncertainties. This work uses a known source, a coal-fired power plant, to explore those errors. The known emissions amount and location remove two major types of error, facilitating understanding of other types. Biases and random errors are distinguished. A Lagrangian dispersion model (HYSPLIT) is run forward in time from the known source, and virtual measurements of the resulting tracer plume are compared to actual measurements from research aircraft. Four flights in different years are used to illustrate a variety of conditions. The measurements are analyzed by a mass-balance method, and the assumptions of that method are discussed. Some of those assumptions can be relaxed in analysis of the modeled plume, allowing testing of their validity. Meteorological fields to drive HYSPLIT are provided by the European Center for Medium Range Weather Forecasts Fifth Reanalysis (ERA5). A unique feature of this work is the use of an ensemble of meteorological fields intrinsic to ERA5. This analysis supports reasonably large (30–40 %) uncertainties on top-down analyses. </jats:p

A Transect of 200 Shallow Shear-Velocity Profiles across the Los Angeles Basin

This study assesses a 60 km north-northeast–south-southwest transect along the San Gabriel River for shallow shear velocities, in San Gabriel Valley and the Los Angeles Basin of southern California. We assessed a total of 214 sites, 199 along the transect at 300-m spacing, during a one-week field campaign with the refraction microtremor (ReMi) technique. The transect's maximum 30-m shear velocity (Vs30) occurs in coarse alluvium of San Gabriel Valley where the San Gabriel River exits the San Gabriel Mountains, at 730 m/sec, upper National Earthquake Hazards Reduction Program (nehrp) site class C. Much of the northeast section of the transect (in San Gabriel Valley) is also nehrp class C, or near the CD class boundary. The section of the transect south from Whittier Narrows to Seal Beach shows nehrp-D velocities in active alluvium. The transect's lowest Vs30, 230 m/ sec at the Alamitos Bay estuary, is also classed as nehrp-D. An increase toward the nehrp CD class boundary occurs at the shoreline beach outside Alamitos Bay, confirmed by additional measurements on Seal Beach. Our measured Vs30 values generally show good correlation with published site-classification maps and existing borehole data sets. There is no evidence in our data for an increase in velocity predicted by Wills et al. (2000) at their CD to BC site classification boundary at the San Gabriel Mountains front, nor for any decrease at their D to DE class boundary at Alamitos Bay. Very large Vs30 variations exist in soil and geologic units sampled by our survey. The Vs30 variations we measured are smaller than Vs30 variations of 30% or more we found between closely spaced (<0.5 km) downhole measurements in the Los Angeles Basin, which are not uncommon within a community data set we examined showing hundreds of boreholes. We find the San Gabriel River's hydraulic gradient to be a good predictor of minimum Vs30, based on the expected effect of the hydraulic gradient on the grain size of sediments deposited by a river. The Vs30 data show a fractal spatial dependence, which appears at distances greater than 700 m. The unprecedented number of shear-velocity measurements we have made suggests that large measurement populations may be necessary to properly characterize Vs30 trends within any surficial geological unit