Airborne MAX-DOAS Measurements Over California: Testing the NASA OMI Tropospheric NO2 Product

Airborne Multi-AXis Differential Optical Absorption Spectroscopy (AMAX-DOAS) measurements of NO2 tropospheric vertical columns were performed over California for two months in summer 2010. The observations are compared to the NASA Ozone Monitoring Instrument (OMI) tropospheric vertical columns (data product v2.1) in two ways: (1) Median data were compared for the whole time period for selected boxes, and the agreement was found to be fair (R = 0.97, slope = 1.4 +/- 0.1, N= 10). (2) A comparison was performed on the mean of coincident AMAX-DOAS measurements within the area of the corresponding OMI pixels with the tropospheric NASA OMI NO2 assigned to that pixel. The effects of different data filters were assessed. Excellent agreement and a strong correlation (R = 0.85, slope = 1.05 +/- 0.09, N= 56) was found for (2) when the data were filtered to eliminate large pixels near the edge of the OMI orbit, the cloud radiance fraction was2 km, and a representative sample of the footprint was taken by the AMAX-DOAS instrument. The AMAX-DOAS and OMI data sets both show a reduction of NO2 tropospheric columns on weekends by 38 +/- 24% and 33 +/- 11%, respectively. The assumptions in the tropospheric satellite air mass factor simulations were tested using independent measurements of surface albedo, aerosol extinction, and NO2 profiles for Los Angeles for July 2010 indicating an uncertainty of 12%

Measurements from the RV Ronald H. Brown and related platforms as part of the Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC)

The Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC) took place from 7&nbsp;January to 11&nbsp;July&nbsp;2020 in the tropical North Atlantic between the eastern edge of Barbados and 51∘&thinsp;W, the longitude of the Northwest Tropical Atlantic Station (NTAS) mooring. Measurements were made to gather information on shallow atmospheric convection, the effects of aerosols and clouds on the ocean surface energy budget, and mesoscale oceanic processes. Multiple platforms were deployed during ATOMIC including the NOAA RV Ronald H. Brown (RHB) (7&nbsp;January to 13&nbsp;February) and WP-3D Orion (P-3) aircraft (17&nbsp;January to 10&nbsp;February), the University of Colorado's Robust Autonomous Aerial Vehicle-Endurant Nimble (RAAVEN) uncrewed aerial system (UAS) (24&nbsp;January to 15&nbsp;February), NOAA- and NASA-sponsored Saildrones (12&nbsp;January to 11&nbsp;July), and Surface Velocity Program Salinity (SVPS) surface ocean drifters (23&nbsp;January to 29&nbsp;April). The RV&nbsp;Ronald H. Brown conducted in situ and remote sensing measurements of oceanic and atmospheric properties with an emphasis on mesoscale oceanic&ndash;atmospheric coupling and aerosol&ndash;cloud interactions. In addition, the ship served as a launching pad for Wave Gliders, Surface Wave Instrument Floats with Tracking (SWIFTs), and radiosondes. Details of measurements made from the RV&nbsp;Ronald H. Brown, ship-deployed assets, and other platforms closely coordinated with the ship during ATOMIC are provided here. These platforms include Saildrone 1064 and the RAAVEN UAS as well as the Barbados Cloud Observatory (BCO) and Barbados Atmospheric Chemistry Observatory (BACO). Inter-platform comparisons are presented to assess consistency in the data sets. Data sets from the RV&nbsp;Ronald H. Brown and deployed assets have been quality controlled and are publicly available at NOAA's National Centers for Environmental Information (NCEI) data archive (https://www.ncei.noaa.gov/archive/accession/ATOMIC-2020, last access: 2 April 2021). Point-of-contact information and links to individual data sets with digital object identifiers (DOIs) are provided herein. &nbsp;</p

The CU mobile Solar Occultation Flux instrument: structure functions and emission rates of NH₃, NO₂ and C₂H₆

We describe the University of Colorado mobile Solar Occultation Flux instrument (CU mobile SOF). The instrument consists of a digital mobile solar tracker that is coupled to a Fourier transform spectrometer (FTS) of 0.5 cm−1 resolution and a UV–visible spectrometer (UV–vis) of 0.55 nm resolution. The instrument is used to simultaneously measure the absorption of ammonia (NH3), ethane (C2H6) and nitrogen dioxide (NO2) along the direct solar beam from a moving laboratory. These direct-sun observations provide high photon flux and enable measurements of vertical column densities (VCDs) with geometric air mass factors, high temporal resolution of 2 s and spatial resolution of 5–19 m. It is shown that the instrument line shape (ILS) of the FTS is independent of the azimuth and elevation angle pointing of the solar tracker. Further, collocated measurements next to a high-resolution FTS at the National Center for Atmospheric Research (HR-NCAR-FTS) show that the CU mobile SOF measurements of NH3 and C2H6 are precise and accurate; the VCD error at high signal to noise ratio is 2–7 %. During the Front Range Air Pollution and Photochemistry Experiment (FRAPPE) from 21 July to 3 September 2014 in Colorado, the CU mobile SOF instrument measured median (minimum, maximum) VCDs of 4.3 (0.5, 45)  ×  1016 molecules cm−2 NH3, 0.30 (0.06, 2.23)  ×  1016 molecules cm−2 NO2 and 3.5 (1.5, 7.7)  ×  1016 molecules cm−2 C2H6. All gases were detected in larger 95 % of the spectra recorded in urban, semi-polluted rural and remote rural areas of the Colorado Front Range. We calculate structure functions based on VCDs, which describe the variability of a gas column over distance, and find the largest variability for NH3. The structure functions suggest that currently available satellites resolve about 10 % of the observed NH3 and NO2 VCD variability in the study area. We further quantify the trace gas emission fluxes of NH3 and C2H6 and production rates of NO2 from concentrated animal feeding operations (CAFO) using the mass balance method, i.e., the closed-loop vector integral of the VCD times wind speed along the drive track. Excellent reproducibility is found for NH3 fluxes and also, to a lesser extent, NO2 production rates on 2 consecutive days; for C2H6 the fluxes are affected by variable upwind conditions. Average emission factors were 12.0 and 11.4 gNH3 h−1 head−1 at 30 °C for feedlots with a combined capacity for  ∼  54 000 cattle and a dairy farm of  ∼  7400 cattle; the pooled rate of 11.8 ± 2.0 gNH3 h−1 head−1 is compatible with the upper range of literature values. At this emission rate the NH3 source from cattle in Weld County, CO (535 766 cattle), could be underestimated by a factor of 2–10. CAFO soils are found to be a significant source of NOx. The NOx source accounts for  ∼  1.2 % of the N flux in NH3 and has the potential to add  ∼  10 % to the overall NOx emissions in Weld County and double the NOx source in remote areas. This potential of CAFO to influence ambient NOx concentrations on the regional scale is relevant because O3 formation is NOx sensitive in the Colorado Front Range. Emissions of NH3 and NOx are relevant for the photochemical O3 and secondary aerosol formation

The Fires, Asian, and Stratospheric Transport-Las Vegas Ozone Study (FAST-LVOS)

The Fires, Asian, and Stratospheric Transport&ndash;Las Vegas Ozone Study (FAST-LVOS) was conducted in May and June of 2017 to study the transport of ozone (O3) to Clark County, Nevada, a marginal non-attainment area in the southwestern United States (SWUS). This 6-week (20&nbsp;May&ndash;30&nbsp;June 2017) field campaign used lidar, ozonesonde, aircraft, and in situ measurements in conjunction with a variety of models to characterize the distribution of O3 and related species above southern Nevada and neighboring California and to probe the influence of stratospheric intrusions and wildfires as well as local, regional, and Asian pollution on surface O3 concentrations in the Las Vegas Valley (&asymp;&thinsp;900&thinsp;m above sea level, a.s.l.). In this paper, we describe the FAST-LVOS campaign and present case studies illustrating the influence of different transport processes on background O3 in Clark County and southern Nevada. The companion paper by Zhang et al.&nbsp;(2020) describes the use of the AM4 and GEOS-Chem global models to simulate the measurements and estimate the impacts of transported O3 on surface air quality across the greater southwestern US and Intermountain West. The FAST-LVOS measurements found elevated O3 layers above Las Vegas on more than 75&thinsp;% (35 of 45) of the sample days and show that entrainment of these layers contributed to mean 8&thinsp;h average regional background O3 concentrations of 50&ndash;55 parts per billion by volume (ppbv), or about 85&ndash;95&thinsp;&micro;g&thinsp;m&minus;3. These high background concentrations constitute 70&thinsp;%&ndash;80&thinsp;% of the current US National Ambient Air Quality Standard (NAAQS) of 70&thinsp;ppbv (&asymp;&thinsp;120&thinsp;&micro;g&thinsp;m&minus;3 at 900&thinsp;m&thinsp;a.s.l.) for the daily maximum 8&thinsp;h average (MDA8) and will make attainment of the more stringent standards of 60 or 65&thinsp;ppbv currently being considered extremely difficult in the interior SWUS. &nbsp;</p

BrO and inferred Br-y profiles over the western Pacific: relevance of inorganic bromine sources and a Br-y minimum in the aged tropical tropopause layer

We report measurements of bromine monoxide (BrO) and use an observationally constrained chemical box model to infer total gas-phase inorganic bromine (Bry) over the tropical western Pacific Ocean (tWPO) during the CONTRAST field campaign (January–February 2014). The observed BrO and inferred Bry profiles peak in the marine boundary layer (MBL), suggesting the need for a bromine source from sea-salt aerosol (SSA), in addition to organic bromine (CBry). Both profiles are found to be C-shaped with local maxima in the upper free troposphere (FT). The median tropospheric BrO vertical column density (VCD) was measured as 1.6×1013 molec cm−2, compared to model predictions of 0.9×1013 molec cm−2 in GEOS-Chem (CBry but no SSA source), 0.4×1013 molec cm−2 in CAM-Chem (CBry and SSA), and 2.1×1013 molec cm−2 in GEOS-Chem (CBry and SSA). Neither global model fully captures the C-shape of the Bry profile. A local Bry maximum of 3.6 ppt (2.9–4.4 ppt; 95 % confidence interval, CI) is inferred between 9.5 and 13.5 km in air masses influenced by recent convective outflow. Unlike BrO, which increases from the convective tropical tropopause layer (TTL) to the aged TTL, gas-phase Bry decreases from the convective TTL to the aged TTL. Analysis of gas-phase Bry against multiple tracers (CFC-11, H2O ∕ O3 ratio, and potential temperature) reveals a Bry minimum of 2.7 ppt (2.3–3.1 ppt; 95 % CI) in the aged TTL, which agrees closely with a stratospheric injection of 2.6 ± 0.6 ppt of inorganic Bry (estimated from CFC-11 correlations), and is remarkably insensitive to assumptions about heterogeneous chemistry. Bry increases to 6.3 ppt (5.6–7.0 ppt; 95 % CI) in the stratospheric "middleworld" and 6.9 ppt (6.5–7.3 ppt; 95 % CI) in the stratospheric "overworld". The local Bry minimum in the aged TTL is qualitatively (but not quantitatively) captured by CAM-Chem, and suggests a more complex partitioning of gas-phase and aerosol Bry species than previously recognized. Our data provide corroborating evidence that inorganic bromine sources (e.g., SSA-derived gas-phase Bry) are needed to explain the gas-phase Bry budget in the upper free troposphere and TTL. They are also consistent with observations of significant bromide in Upper Troposphere–Lower Stratosphere aerosols. The total Bry budget in the TTL is currently not closed, because of the lack of concurrent quantitative measurements of gas-phase Bry species (i.e., BrO, HOBr, HBr, etc.) and aerosol bromide. Such simultaneous measurements are needed to (1) quantify SSA-derived Bry in the upper FT, (2) test Bry partitioning, and possibly explain the gas-phase Bry minimum in the aged TTL, (3) constrain heterogeneous reaction rates of bromine, and (4) account for all of the sources of Bry to the lower stratosphere

Combining Active and Passive Airborne Remote Sensing to Quantify NO2 and Ox Production near Bakersfield, CA

Aims: The objective of this study is to demonstrate the integrated use of passive and active remote sensing instruments to quantify the rate of NOx emissions, and investigate the Ox production rates from an urban area.Place and Duration of Study: A research flight on June 15, 2010 was conducted over Bakersfield, CA and nearby areas with oil and natural gas production. Methodology: Three remote sensing instruments, namely the University of Colorado AMAX-DOAS, NOAA TOPAZ lidar, and NCAS Doppler lidar were deployed aboard the NOAA Twin Otter during summer 2010. Production rates of nitrogen dioxide (NO2) and Ox&lsquo;(background corrected O3 + NO2) were quantified using the horizontal flux divergence approach by flying closed loops near Bakersfield, CA. By making concurrent measurements of the trace gases as well as the wind fields, we have reduced the uncertainty due to wind field in production rates.Results: We find that the entire region is a source for both NO2 and Ox&rsquo;. NO2 production is highest over the city (1.35 kg hr-1 km-2 NO2), and about 30 times lower at background sites (0.04 kg hr-1 km-2 NO2). NOx emissions as represented in the CARB 2010 emission inventory agreewell with our measurements over Bakersfield city (within 30%). However, emissions upwind of the city are significantly underestimated. The Ox&rsquo; production is less variable, found ubiquitous, and accounts for 7.4 kg hr-1 km-2 Ox&rsquo; at background sites. Interestingly, the maximum of 17.1 kg hr-1 km-2 Ox&rsquo;production was observed upwind of the city. A plausible explanation for the efficient Ox&rsquo; production upwind of Bakersfield, CA are favorable volatile organic compound (VOC) to NOx ratios for Ox&rsquo; production, that are affected by emissions from large oil and natural gas operations in that area. Conclusion: The NO2 and O3 source fluxes vary significantly, and allow us to separate and map NOx emissions and Ox production rates in the Central Valley. The data is probed over spatial scales that link closely with those predicted by atmospheric models, and provide innovative means to test and improve atmospheric models that are used to manage air resources. Emissions from oil and natural gas operations are a source for O3 air pollution, and deserve further study to better characterize effects on public health.</p

Quantitative detection of iodine in the stratosphere

Oceanic emissions of iodine destroy ozone, modify oxidative capacity, and can form new particles in the troposphere. However, the impact of iodine in the stratosphere is highly uncertain due to the lack of previous quantitative measurements. Here, we report quantitative measurements of iodine monoxide radicals and particulate iodine (Iy,part) from aircraft in the stratosphere. These measurements support that 0.77 ± 0.10 parts per trillion by volume (pptv) total inorganic iodine (Iy) is injected to the stratosphere. These high Iy amounts are indicative of active iodine recycling on ice in the upper troposphere (UT), support the upper end of recent Iy estimates (0 to 0.8 pptv) by the World Meteorological Organization, and are incompatible with zero stratospheric iodine injection. Gasphase iodine (Iy,gas) in the UT (0.67 ± 0.09 pptv) converts to Iy,part sharply near the tropopause. In the stratosphere, IO radicals remain detectable (0.06 ± 0.03 pptv), indicating persistent Iy,part recycling back to Iy,gas as a result of active multiphase chemistry. At the observed levels, iodine is responsible for 32% of the halogen-induced ozone loss (bromine 40%, chlorine 28%), due primarily to previously unconsidered heterogeneous chemistry. Anthropogenic (pollution) ozone has increased iodine emissions since preindustrial times (ca. factor of 3 since 1950) and could be partly responsible for the continued decrease of ozone in the lower stratosphere. Increasing iodine emissions have implications for ozone radiative forcing and possibly new particle formation near the tropopause.Fil: Koenig, Theodore K.. State University of Colorado at Boulder; Estados UnidosFil: Baidar, Sunil. State University of Colorado at Boulder; Estados UnidosFil: Campuzano Jost, Pedro. State University of Colorado at Boulder; Estados UnidosFil: Cuevas, Carlos Alberto. Consejo Superior de Investigaciones Científicas. Instituto de Química Física; EspañaFil: Dix, Barbara. State University of Colorado at Boulder; Estados UnidosFil: Fernandez, Rafael Pedro. Consejo Superior de Investigaciones Científicas. Instituto de Química Física; España. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Interdisciplinario de Ciencias Básicas. - Universidad Nacional de Cuyo. Instituto Interdisciplinario de Ciencias Básicas; ArgentinaFil: Guo, Hongyu. State University of Colorado at Boulder; Estados UnidosFil: Hall, Samuel R.. National Center for Atmospheric Research; Estados UnidosFil: Kinnison, Douglas. National Center for Atmospheric Research; Estados UnidosFil: Nault, Benjamin A.. State University of Colorado at Boulder; Estados UnidosFil: Ullmann, Kirk. National Center for Atmospheric Research; Estados UnidosFil: Jimenez, Jose L.. State University of Colorado at Boulder; Estados UnidosFil: Saiz López, Alfonso. Consejo Superior de Investigaciones Científicas. Instituto de Química Física; EspañaFil: Volkamer, Rainer. State University of Colorado at Boulder; Estados Unido

Stratospheric Injection of Brominated Very Short‐Lived Substances: Aircraft Observations in the Western Pacific and Representation in Global Models

We quantify the stratospheric injection of brominated very short‐lived substances (VSLS) based on aircraft observations acquired in winter 2014 above the Tropical Western Pacific during the CONvective TRansport of Active Species in the Tropics (CONTRAST) and the Airborne Tropical TRopopause EXperiment (ATTREX) campaigns. The overall contribution of VSLS to stratospheric bromine was determined to be 5.0 ± 2.1 ppt, in agreement with the 5 ± 3 ppt estimate provided in the 2014 World Meteorological Organization (WMO) Ozone Assessment report (WMO 2014), but with lower uncertainty. Measurements of organic bromine compounds, including VSLS, were analyzed using CFC‐11 as a reference stratospheric tracer. From this analysis, 2.9 ± 0.6 ppt of bromine enters the stratosphere via organic source gas injection of VSLS. This value is two times the mean bromine content of VSLS measured at the tropical tropopause, for regions outside of the Tropical Western Pacific, summarized in WMO 2014. A photochemical box model, constrained to CONTRAST observations, was used to estimate inorganic bromine from measurements of BrO collected by two instruments. The analysis indicates that 2.1 ± 2.1 ppt of bromine enters the stratosphere via inorganic product gas injection. We also examine the representation of brominated VSLS within 14 global models that participated in the Chemistry‐Climate Model Initiative. The representation of stratospheric bromine in these models generally lies within the range of our empirical estimate. Models that include explicit representations of VSLS compare better with bromine observations in the lower stratosphere than models that utilize longer‐lived chemicals as a surrogate for VSLS

Airborne Multi-Axis and Direct Sun DOAS: Development and Urban Air Quality Applications

Tropospheric ozone (O3) is one of the most prevalent air pollutants affecting human health and environment. It is also a greenhouse gas. O3 is a secondary pollutant formed in the atmosphere by the chemical reaction between nitrogen oxides (NOx) and volatile organic compounds (VOC) in the presence of sunlight, and a major constituent of photochemical smog. The O3 formation is a complex non-linear process which depends on NOx and VOC reactivity. As a result, reduction in emissions of precursor molecules do not always result in decrease in O3 levels. Occurrence of higher O3 on weekends in an urban environment as a response to reductions in NOx emissions is commonly referred as the weekend O3 effect. The Airborne Multi-Axis Differential Optical Absorption Spectroscopy (AMAX-DOAS) was deployed aboard the NOAA Twin Otter during the California Research at the Nexus of Air Quality and Climate Change (CalNex) and Carbonaceous Aerosols and Radiative Effects Study (CARES) field campaigns in summer 2010 in California to measure vertical profiles and columns of O3 precursor molecules nitrogen dioxide (NO2), formaldehyde (HCHO) and glyoxal (CHOCHO). Measurements from the two campaigns have been used extensively for evaluation of satellite measurements and atmospheric models over California. This work describes the instrument, retrievals of NO2, HCHO and CHOCHO vertical profiles and columns from the measurements and the validation of the NO2 columns. In addition, application of three remote sensing instruments (AMAX-DOAS, NOAA TOPAZ O3 and Doppler wind lidars) to constrain NO2 and Ox (O3 + NO2) production rates from source regions in Bakersfield, CA is presented. I also present analysis of the aircraft and long term surface network measurements of NO2 and O3 showing recent weakening of the weekend O3 effect in California’s South Coast Air Basin. AMAX-DOAS measurements were also used to confirm the sand signal observed by satellite-borne instruments over deserts. A mobile solar tracker was developed for direct sun DOAS measurements of NO2 and other trace gases. It features an integrated motion compensation system and an imaging feedback loop allowing for autonomous sun tracking at very high precision from a mobile laboratory. Advantages of direct sun measurements over scattered sunlight include high photon flux, simple conversion of slant columns to vertical columns, and no Ring effect, all of which results in the improvement in measurement precision. This allows for mapping of temporal and spatial variability in NO2 columns with unprecedented detail. The tracker can be simultaneously coupled with UV-vis and FTIR spectrometers. Results from its first deployment during Front Range Air Pollution and Photochemistry Experiment (FRAPPE) in Colorado are presented

Airborne tests of an OAWL Doppler lidar: Results and potential for space deployment

The 532 nm Green Optical Covariance Wind Lidar (GrOAWL) was flown on a NASA WB-57 research aircraft during the summer of 2016 to validate the instrument design and evaluate wind measurement capability and sensitivity. Comparisons with dropsondes and atmospheric models showed good agreement, demonstrating that a GrOAWL type instrument could provide high-value wind measurements from both airborne and space-based platform