Spectral surface albedo, a boundary condition which needs to be accurately known for aerosol remote sensing, surface aerosol forcing, and radiative transfer calculations, also strongly affects ...Earth's radiation balance. The difficulty in deriving surface albedo from space and aircraft observations lies mainly in the atmospheric correction, especially in aerosol‐burdened regions. Because of the different scales, comparing satellite retrievals with airborne or ground‐based observations is not straightforward. We use Solar Spectral Flux Radiometer (SSFR) measurements of upward and downward irradiance from aircraft altitude during Megacity Initiative: Local and Global Research Observations (MILAGRO) to determine spectral surface albedo at ground stations and along the flight track (over the wavelength range 350 to 2100 nm), thereby linking flight‐level retrieved measurements to larger‐scale satellite observations in the polluted Mexico City environment. Our approach involves iteratively adjusting the surface albedo input of a SSFR specific radiative transfer model until the modeled upward irradiance matches the SSFR measurements at flight level. A sensitivity analysis of surface albedo to aerosol optical properties provides a retrieval uncertainty, which can outweigh the SSFR instrument uncertainty under highly variable conditions (or uncertain measurements) of aerosol optical depth and asymmetry parameter. Comparisons between spectral surface albedo derived from the SSFR, Multi‐Filter Rotating Shadowband Radiometer, and the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument onboard the NASA‐EOS Terra and Aqua satellites are shown with differences of 6–10% and 0.025–0.05 units, respectively. Along‐track comparisons between the SSFR and MODIS show that two instruments (aircraft and satellite) can capture inhomogeneous surface albedo scene changes.
The accuracy with which vertical profiles of aerosol extinction σep(λ) can be measured using routine Atmospheric Radiation Measurement Program (ARM) Climate Research Facility (ACRF) measurements and ...was assessed using data from two airborne field campaigns, the ARM Aerosol Intensive Operation Period (AIOP, May 2003), and the Aerosol Lidar Validation Experiment (ALIVE, September 2005). This assessment pertains to the aerosol at its ambient concentration and thermodynamic state (i.e., σep(λ) either free of or corrected for sampling artifacts) and includes the following ACRF routine methods: Raman lidar, micropulse lidar (MPL), and in situ aerosol profiles (IAP) with a small aircraft. Profiles of aerosol optical depth τp(λ), from which the profiles of σep(λ) are derived through vertical differentiation, were measured by the NASA Ames Airborne Tracking 14‐channel Sun photometer (AATS‐14); these data were used as benchmark in this evaluation. The ACRF IAP σep(550 nm) were lower by 11% (during AIOP) and higher by 1% (during ALIVE) when compared to AATS‐14. The ACRF MPL σep(523 nm) measurements were higher by 24% (AIOP) and 19–21% (ALIVE) compared to AATS‐14, but the correlation improved significantly during ALIVE. In the AIOP, a second MPL operated by NASA showed a smaller positive bias (13%) with respect to AATS‐14. The ACRF Raman lidar σep(355 nm) measurements were larger by 54% (AIOP) and by 6% (ALIVE) compared to AATS‐14. The large bias in the Raman lidar measurements during AIOP stemmed from a gradual loss of Raman lidar sensitivity starting about the end of 2001 going unnoticed until after AIOP. A major refurbishment and upgrade of the instrument and improvements to a data processing algorithm led to the significant improvement and very small bias in ALIVE. Finally, we find that during ALIVE the Raman lidar water vapor densities ρw are 8% larger when compared to AATS‐14, whereas in situ measured ρw aboard two different aircraft are smaller than the AATS‐14 values by 0.3–3%.
As part of the INTEX‐NA (Intercontinental chemical Transport Experiment–North America) and ITCT (Intercontinental Transport and Chemical Transformation of anthropogenic pollution) field studies, the ...NASA Ames 14‐channel Airborne Tracking Sunphotometer (AATS‐14) and a pair of Solar Spectral Flux Radiometers (SSFR) took measurements from aboard a Sky Research Jet stream 31 (J31) aircraft during 19 science flights over the Gulf of Maine during 12 July to 8 August 2004. The combination of coincident AATS‐14 and SSFR measurements yields plots of net (downwelling minus upwelling) spectral irradiance as a function of aerosol optical depth (AOD) as measured along horizontal flight legs. By definition, the slope of these plots yields the instantaneous change in net irradiance per unit AOD change and is referred to as the instantaneous spectral aerosol radiative forcing efficiency, Ei (W m−2 nm−1). Numerical integration over a given spectral range yields the instantaneous broadband aerosol radiative forcing efficiency (W m−2). This technique for deriving Ei is called the aerosol gradient method. Within 10 case studies considered suitable for our analysis we found a high variability in the derived instantaneous aerosol forcing efficiencies for the visible wavelength range (350–700 nm), with a mean of −79.6 W m−2 and a standard deviation of 21.8 W m−2 (27%). An analytical conversion of the instantaneous forcing efficiencies to 24‐hour‐average values yielded −45.8 ± 13.1 W m−2 (mean ± std). We present spectrally resolved aerosol forcing efficiencies between 350 and 1670 nm, estimates of the midvisible aerosol single scattering albedo and a comparison of observed broadband forcing efficiencies to previously reported values.
High ozone (O3) concentrations at low altitudes (1.5–4 km) were detected from airborne Alpha Jet Atmospheric eXperiment (AJAX) measurements on 30 May 2012 off the coast of California (CA). We ...investigate the causes of those elevated O3 concentrations using airborne measurements and various models. GEOS-Chem simulation shows that the contribution from local sources is likely small. A back-trajectory model was used to determine the air mass origins and how much they contributed to the O3 over CA. Low-level potential vorticity (PV) from Modern Era Retrospective analysis for Research and Applications 2 (MERRA-2) reanalysis data appears to be a result of the diabatic heating and mixing of airs in the lower altitudes, rather than be a result of direct transport from stratospheric intrusion. The Q diagnostic, which is a measure of the mixing of the air masses, indicates that there is sufficient mixing along the trajectory to indicate that O3 from the different origins is mixed and transported to the western U.S.
The back-trajectory model simulation demonstrates the air masses of interest came mostly from the mid troposphere (MT, 76%), but the contribution of the lower troposphere (LT, 19%) is also significant compared to those from the upper troposphere/lower stratosphere (UT/LS, 5%). Air coming from the LT appears to be mostly originating over Asia. The possible surface impact of the high O3 transported aloft on the surface O3 concentration through vertical and horizontal transport within a few days is substantiated by the influence maps determined from the Weather Research and Forecasting–Stochastic Time Inverted Lagrangian Transport (WRF-STILT) model and the observed increases in surface ozone mixing ratios. Contrasting this complex case with a stratospheric-dominant event emphasizes the contribution of each source to the high O3 concentration in the lower altitudes over CA. Integrated analyses using models, reanalysis, and diagnostic tools, allows high ozone values detected by in-situ measurements to be attributed to multiple source processes.
•High O3 at 1–4 km shows complex origins; only small influence from N. America and stratosphere.•Transport from Asian boundary layer followed by mixing with mid tropospheric air.•The Q diagnostic is a measure of the mixing of the air masses.•Integrated analysis with models, reanalysis & diagnostics allows source assessment.•WRF-STILT identifies surface impact a few days after sampling.
Deserts are fragile and highly sensitive ecosystems that increasingly are affected by upwind urban areas and industrial activities. The Los Angeles Basin (LAB) contributes to poor air quality in ...downwind deserts including the Mojave Desert. Few studies have investigated potential air pollution inputs to the Mojave, whose fragile ecosystem includes endangered plant and animal species.
Data were collected on 19 August 2015 by a mobile air quality laboratory, AMOG (AutoMObile trace Gas) Surveyor, that observed inputs can arise from the LAB as well as the San Joaquin Valley (SJV), California. The campaign used a strong methane (CH4) plume as a tracer for the downwind fate of emissions from Bakersfield area petroleum production and also measured ozone (O3). Additional in situ concurrent airborne GHG and O3 data were collected by AJAX - Alpha Jet Atmospheric eXperiment. Both AMOG and AJAX measure winds.
Mojave Desert air quality was very poor (visibility ~4 km). Based on the winds, an additional source was inferred beyond the LAB and SJV Basins. Numerical transport modeling and analysis of aerosol lidar data collected the same day by the Cloud Profiling LiDAR onboard the Earth Research-2 stratospheric airplane demonstrated that fires in Northern California were responsible, with prevailing winds transporting air southwards along the eastern Sierra Nevada Range (Bishop Valley) to the Mojave.
Whereas the southern and eastern Mojave are impacted by SJV and LAB outflow, the north Mojave generally avoids these inputs. This study shows it can be affected by even distant wildfires, which likely will increase in occurrence and intensity from climate change. Thus, regulatory efforts to reduce air quality impacts on the endangered Mojave ecosystem must include wildfires and also account for the significant differences between different regions of the Mojave. Currently, there is a paucity of studies, highlighting the critical need for field research.
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•Kern oil field's air flows through the Tehachapi Pass to the Mojave Desert.•Mojave air quality can be reduced by fire to the north, through the Owens Valley.•San Joaquin Valley and Los Angeles and fire pollution mix in the Mojave Desert.•Climate change will increase the importance of fire air pollution to the Mojave.
The NASA Ames Research Center operates a new research platform for atmospheric studies: an instrumented Alpha Jet. The present complement of instruments allows for the determination of carbon ...dioxide, ozone, water vapor, and methane concentrations as well as measurements of three-dimensional wind speeds, temperature, and pressure. Planned future instrumentation includes an Air-Core sampler and an instrument to measure formaldehyde. We give examples of measurements that have been made, including measurements carried out during a downward spiral over an expected methane source. An attractive property of this airborne system is its ability to respond rapidly to unexpected atmospheric events such as large forest fires or severe air quality events.
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Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
In this paper, we report the vertical profiles of CO 2 and CH 4 measured with a cavity ring-down spectrometer (CRDS) on a research aircraft from near-ground level to 8 km above mean sea level. The ...airborne platform employed in this paper is an Alpha Jet aircraft operated from NASA's Ames Research Center. Flights were undertaken to Railroad Valley, NV, USA, to coincide with overpasses of the Greenhouse Gases Observing Satellite (GOSAT). Ground-based CO 2 and CH 4 were simultaneously measured using CRDS, at the time and location of the airborne and satellite measurements. Results of three GOSAT coordinated aircraft profiles and ground-based measurements in June 2011 are presented and discussed in this paper. The accuracy of the CO 2 and CH 4 measurements has been determined based upon laboratory calibrations (World Meteorological Organisation traceable standard) and pressure/temperature flight simulations in a test chamber. The overall uncertainty for the airborne measurements ranged from 0.31 to 0.39 ppm for CO 2 and from 3.5 to 5.6 ppb for CH 4 . Our column-averaged CO 2 and CH 4 measurements, which include about 61% of the total atmospheric mass, are extrapolated, using different techniques, to include the remainder of the tropospheric and stratospheric CO 2 and CH 4 . The CO 2 data are then analyzed using the Atmospheric CO 2 Observations from Space 2.9 and 3.3 algorithms. For methane data, the RemoTeC v2.1 algorithm was used in its full physics setup. Column-averaged CO 2 and XCO 2 , measured by GOSAT and analyzed from our data, ranged from 388.1 to 396.4 ppm, and XCH 4 ranged from 1.743 to 1.822 ppm. The agreement of the satellite and aircraft CO 2 mixing ratios, as well as ground measurements, falls within the uncertainties of the methods employed to acquire these numbers.
Atmospheric Radiation Measurements Enhanced Shortwave Experiment (ARESE) was conducted to study the magnitude and spectral characteristics of the absorption of solar radiation by the clear and cloudy ...atmosphere. Three aircraft platforms, a Grob Egrett, a NASA ER‐2, and a Twin Otter, were used during ARESE in conjunction with the Atmospheric Radiation Measurements (ARM) central and extended facilities in north central Oklahoma. The aircraft were coordinated to simultaneously measure solar irradiances in the total spectral broadband (0.224–3.91 μm), near infrared broadband (0.678–3.3 μm), and in seven narrow band‐pass (∼10 nm width) channels centered at 0.500, 0.862, 1.064, 1.249, 1.501, 1.651, and 1.750 μm. Instrumental calibration issues are discussed in some detail, in particular radiometric power, angular, and spectral responses. The data discussed in this paper are available at the ARM ARESE data archive via anonymous FTP to ftp.arm.gov.
The Alpha Jet Atmospheric eXperiment (AJAX) is a project to measure the atmospheric profiles of greenhouse gases (GHGs) and ozone (O 3 ) regularly over California and Nevada. Airborne instruments ...measuring GHGs and O 3 are installed in a wing pod of an Alpha Jet aircraft and operated from the National Aeronautics and Space Administration Ames Research Center at Moffett Field, CA. The instruments yield precise and accurate in situ vertical profiles of atmospheric carbon dioxide (CO 2 ), methane (CH 4 ), and O 3 . Measurements of vertical profiles of GHGs and O 3 over Railroad Valley, NV have been conducted directly under the Greenhouse gases Observing SATellite (GOSAT) over passes on a monthly basis as part of the AJAX project since June 2011. The purpose of this work is to calculate aircraft-based dry-air mole fractions of the GHGs for the validation of GOSAT data products. This study expands and improves our previous comparisons by evaluating three algorithms against 24 months of in situ data collected over a Gain-M target. We used three different algorithms: Atmospheric CO 2 Observations from Space (ACOS v3.4r3), Remote Sensing of Greenhouse Gases for Carbon Cycle Modeling (RemoteC v2.3.5FP), and National Institute for Environmental Studies (NIES v2.11). We find that the CO 2 average differences of ACOS and RemoteC from AJAX are 0.26% and 0.24%, respectively. The difference between NIES and AJAX is 0.96%, which is higher than that of ACOS and RemoteC. The CH 4 average differences for RemoteC and NIES are 2.1% and 1.7%, respectively.
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