Publications

Methane emissions from the 2015 Aliso Canyon blowout in Los Angeles, CA

Single-point failures of natural gas infrastructure can hamper methane emission control strategies designed to mitigate climate change. The 23 October 2015 blowout of a well connected to the Aliso Canyon underground storage facility in California resulted in a massive release of natural gas. Analysis of methane and ethane data from dozens of plume transects, collected during 13 research-aircraft flights between 7 November 2015 and 13 February 2016, shows atmospheric leak rates of up to 60 metric tons of methane and 4.5 metric tons of ethane per hour. At its peak, this blowout effectively doubled the methane emission rate of the entire Los Angeles basin and, in total, released 97,100 metric tons of methane to the atmosphere.

Impact of Asian continental outflow on the concentrations of O3, CO, NMHCs and halocarbons on Jeju Island, South Korea during March 2005

Diurnal Trends Differentiate Anthropogenic and Biogenic Terpenes in the Los Angeles Basin

Terpenoids play a significant role in the formation of tropospheric ozone (O3) and secondary organic aerosol (SOA). While terpenoids are largely attributed to biogenic sources, they are also widely used in consumer products that end up in the atmosphe

The Chemistry Mechanism in the Community Earth System Model Version 2 (CESM2)

Abstract The Community Earth System Model version 2 (CESM2) includes a detailed representation of chemistry throughout the atmosphere in the Community Atmosphere Model with chemistry and Whole Atmosphere Community Climate Model configurations. These model configurations use the Model for Ozone and Related chemical Tracers (MOZART) family of chemical mechanisms, covering the troposphere, stratosphere, mesosphere, and lower thermosphere. The new MOZART tropospheric chemistry scheme (T1) has a number of updates over the previous version (MOZART‐4) in CESM, including improvements to the oxidation of isoprene and terpenes, organic nitrate speciation, and aromatic speciation and oxidation and thus improved representation of ozone and secondary organic aerosol precursors. An evaluation of the present‐day simulations of CESM2 being provided for Climate Model Intercomparison Project round 6 (CMIP6) is presented. These simulations, using the anthropogenic and biomass burning emissions from the inventories specified for CMIP6, as well as online calculation of emissions of biogenic compounds, lightning NO, dust, and sea salt, indicate an underestimate of anthropogenic emissions of a variety of compounds, including carbon monoxide and hydrocarbons. The simulation of surface ozone in the southeast United States is improved over previous model versions, largely due to the improved representation of reactive nitrogen and organic nitrate compounds resulting in a lower ozone production rate than in CESM1 but still overestimates observations in summer. The simulation of tropospheric ozone agrees well with ozonesonde observations in many parts of the globe. The comparison of NO x and PAN to aircraft observations indicates the model simulates the nitrogen budget well.

Supplementary material to "The Global Methane Budget 2000–2017"

Transport of anthropogenic emissions during ARCTAS-A: a climatology and regional case studies

Abstract. The National Aeronautics and Space Administration (NASA) conducted the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) mission during 2008 as a part of the International Polar Year (IPY). The purpose of ARCTAS was to study the factors responsible for changes in the Arctic's atmospheric composition and climate. A major emphasis was to investigate Arctic haze, which is most pronounced during winter and early spring. This study focuses on the spring phase of ARCTAS (ARCTAS-A) that was based in Alaska during April 2008. Although anthropogenic emissions historically have been associated with Arctic haze, biomass burning dominated the ARCTAS-A period and has been the focus of many ARCTAS related studies. This study determines the common pathways for anthropogenic emissions during ARCTAS-A. Trajectories (air parcels) are released each day from three historically significant regions of anthropogenic emissions (Asia, North America, and Europe). These fifteen day forward trajectories are calculated using data from the Weather Research and Forecasting (WRF) model at 45 km horizontal resolution. The trajectories then are examined to determine: origins of emissions that reach the Arctic (defined as north of 70° N) within fifteen days, pathways of the emissions reaching the Arctic, Arctic entry locations, and altitudes at which the trajectories enter the Arctic. These results serve as regional "climatologies" for the ARCTAS-A period. Three cases during the ARCTAS-A period (one for each of the regions above) are examined using backward trajectories and chemical fingerprinting based on in situ data sampled from the NASA DC-8. The fingerprinting utilizes volatile organic compounds that represent pure anthropogenic tracers, Asian anthropogenic pollution, incomplete combustion, and natural gas emissions. We determine flight legs containing anthropogenic emissions and the pathways travelled by these emissions. Results show that the DC-8 sampled anthropogenic emissions from Asia, North America, and Europe during the spring phase of ARCTAS. The pathways travelled by these emissions agree with our derived "climatologies" and previous studies of Arctic transport. Meteorological analysis and trajectory calculations indicate that middle latitude cyclones and their associated warm conveyor belts play an important role in lofting the surface based emissions to their sampling altitude in all three cases.

Atmospheric chemistry in the Arctic and subarctic: Influence of natural fires, industrial emissions, and stratospheric inputs

Haze layers with perturbed concentrations of trace gases, believed to originate from tundra and forest wild fires, were observed over extensive areas of Alaska and Canada in 1988. Enhancements of CH 4 , C 2 H 2 , C 2 H 6 , C 3 H 8 , and C 4 H 10 were linearly correlated with CO in haze layers, with mean ratios (mole hydrocarbon/mole CO) of 0.18 (± 0.04 (1 σ)), 0.0019 (± 0.0001), 0.0055 (± 0.0002), 0.0008 (± 0.0001), and 1.2 × 10 −4 (±0.2× 10 −4 ), respectively. Enhancements of NO y , were variable, averaging 0.0056 (± 0.0030) mole NO y /mole CO, while perturbations of NO x were very small, usually undetectable. At least 1/3 of the NO y in the haze layers had been converted to peroxyacetyl nitrate (PAN), representing a potential source of NO x to the global atmosphere; much of the balance was oxidized to nitrate (HNO 3 and paniculate). The composition of sub‐Arctic haze layers was consistent with aged emissions from smoldering combustion, except for CH 4 , which appears to be partly biogenic. Inputs from the stratosphere and from biomass fires contributed major fractions of the NO y in the remote sub‐Arctic troposphere. Analysis of aircraft and ground data indicates relatively little influence from mid‐latitude industrial NO y in this region during summer, possibly excepting transport of PAN. Production of O 3 was inefficient in sub‐Arctic haze layers, less than 0.1 O 3 molecules per molecule of CO, reflecting the low NO x /CO emission ratios from smoldering combustion. Mid‐latitude pollution produced much more O 3 , 0.3 – 0.5 O 3 molecules per molecule of CO, a consequence of higher NO x /CO emission ratios.

Changes In Atmospheric Methane And Its Stable Isotope Signatures Between 1978-2005 Deduced From Interhemispheric Differences and Trends

LBA-ECO TG-10 Fire Emission Factors in Mato Grosso, Para, and Amazonas, Brazil: 2004

This data set provides derived emission factors (EFs), reported in grams of compound emitted per kilogram of dry fuel (g/kg), for PM10 (particulate matter up to 10 micrometers in size), O3, CO2, CO, NO, NO2, HONO, HCN, NH3, OCS, DMS, CH4, and up to 48 non-methane organic compounds (NMOC) from the Tropical Forest and Fire Emissions Experiment (TROFFEE). TROFFEE used laboratory measurements followed by airborne and ground based field campaigns in Mato Grosso, Para, and Amazonas, Brazil during the 2004 Amazon dry season to quantify the emissions from pristine tropical forest and several plantations as well as the emissions, fuel consumption, and fire ecology of tropical deforestation fires. EFs were determined for 19 tropical deforestation fires in August and September, 2004. The combined output of these fires created a massive megaplume more than 500-km wide and covered a large area in Brazil, Bolivia, and Paraguay for about one month. For the megaplume, the EFs (reported in grams of compound emitted per kilogram of dry fuel (g/kg)) represented the effective emissions factor measured downwind from the source. There are two comma-delimited data files (.csv) and one text file (.txt) with this data set. The text file contains information regarding the fuel/fire sources, latitude and longitudes (also provided in the data files).

In Situ Measurement of Stratosperic Intrusions in the Free Troposphere and Boundary Layer During the DC3 Field Campaign

Global budget of ethane and regional constraints on U.S. sources

We use a 3‐D chemical transport model (the GEOS‐Chem CTM) to evaluate a global emission inventory for ethane (C 2 H 6 ), with a best estimate for the global source of 13 Tg yr −1 , 8.0 Tg yr −1 from fossil fuel production, 2.6 Tg yr −1 from biofuel, and 2.4 Tg yr −1 from biomass burning. About 80% of the source is emitted in the Northern Hemisphere. The model generally provides a reasonable and unbiased simulation of surface air observations, column measurements, and aircraft profiles worldwide, including patterns of geographical and seasonal variability. The main bias is a 20%–30% overestimate at European surface sites. Propagation of the C 2 H 6 seasonal signal from northern midlatitudes to the equatorial western Pacific and the southern tropics demonstrates the dominance of northern midlatitudes as a source of C 2 H 6 worldwide. Interhemispheric transport provides the largest C 2 H 6 source to the Southern Hemisphere (1.7 Tg yr −1 ), and southern biomass burning provides the other major source (1.0 Tg yr −1 ). The C 2 H 6 emission inventory for the United States from the Environmental Protection Agency (0.6 Tg yr −1 ) is considerably lower than our estimate constrained by extensive aircraft observations in the continental boundary layer (2.4 Tg yr −1 ). This appears to reflect a factor 7 underestimate in the fossil fuel source over the south‐central United States. Our estimate of C 2 H 6 emissions, together with observed ratios of CH 4 :C 2 H 6 , suggests that CH 4 emissions from energy production in the U.S. may be underestimated by as much as 50%–100%.

Gas Signatures From Cultured Human Leukocytes

Vertical profile and origin of wintertime tropospheric ozone over China during the PEACE‐A period

During the Pacific Exploration of Asian Continental Emission (PEACE) phase A mission in January 2002, we launched ozonesondes in subtropical southeast China at Hong Kong (114.17°E, 22.31°N), middle latitude northeast China at Beijing (116.47°E, 39.81°N), and northwest China at Xining (101.45°E, 36.43°N) in order to study long‐range ozone (O 3 ) transport from Eurasia, tropospheric O 3 sources in China, and O 3 outflow to the Pacific. Tropospheric O 3 showed a complex vertical distribution with average tropospheric O 3 columns of 39 ± 4, 23 ± 3, and 30 ± 6 DU in Hong Kong, Beijing, and Xining, respectively, which accounted for 17 ± 2%, 7 ± 1%, and 10 ± 1% of the total O 3 column. The lower tropospheric and boundary layer (BL) O 3 over Xining and especially Beijing exhibited low values, suggesting negligible O 3 formation in middle latitudes of China during the winter season. The results also revealed frequent propagation of enhanced O 3 layers from the lower stratosphere to the upper troposphere over Xining and especially Beijing, suggesting that stratospheric O 3 is an important source of O 3 in the upper troposphere of northern China. This “natural” O 3 is transported downwind by the prevailing westerly wind and acts as a source of O 3 to the east Asian coast and northwestern Pacific. We observed elevated O 3 , with a maximum mixing ratio up to 111 ppbv, at 1.5 km in the upper BL over Hong Kong. The elevated O 3 was resulted from transport of pollutants from northwest‐central or southwest China and regional O 3 formation and accumulation in south China including the Pearl River Delta and Hong Kong. We also observed enhanced O 3 (>95 ppbv) in the middle and upper troposphere over Hong Kong in air masses transported along the subtropical jet from tropical and subtropical East Africa, south Asia, and Southeast Asia. The O 3 enhancements were most likely due to intrusion of stratospheric O 3 into the troposphere in the Indo‐Burmese region of tropical Southeast Asia, where substantial downward motion had been observed.

Atmospheric Organic Gases from Fossil Fuel Extraction Activities: Analysis and Modeling

Observationally constrained analysis of sulfur cycle in the marine atmosphere with NASA ATom measurements and AeroCom model simulations

Abstract. The sulfur cycle plays a key role in atmospheric air quality, climate, and ecosystems. In this study, we compare the spatial and temporal distribution of four sulfur-containing species, dimethyl sulfide (DMS), sulfur dioxide (SO2), particulate methanesulfonate (MSA), and particulate sulfate (SO4), that were measured during the airborne NASA Atmospheric Tomography (ATom) mission and simulated by five AeroCom-III models to analyze the budget of sulfur cycle from the models. This study focuses on remote regions over the Pacific, Atlantic, and Southern Oceans from near the ocean surface to ~12-km altitude range, and covers all four seasons. These regions provide us with highly heterogeneous natural and anthropogenic source environments, which is not usually the case for traditional continental studies. We examine the vertical and seasonal variations of these sulfur species over tropical, mid-, and high-latitude regions in both hemispheres. We identify their origins from land versus ocean and from anthropogenic versus natural sources with sensitivity studies by applying tagged tracers linking to emission types and regions. In general, the differences among model results can be greater than one-order of magnitude. Comparing with observations, simulated SO2 is generally low while SO4 is high, and the model-observation agreement is much better in ATom-4 (April–May, 2018). There are much larger DMS concentrations simulated close to the sea surface than observed, indicating that the DMS emissions may be too high from all models. Anthropogenic emissions are the dominant source (40–60 % of the total amount) for atmospheric sulfate simulated at locations and times along the ATom flight tracks at almost every altitude, followed by volcanic emissions (18–32 %) and oceanic sources (16–32 %). Similar source contributions can also be derived at broad ocean basin and monthly scales, indicating that any reductions of anthropogenic sulfur emissions would have global impacts in modern times.

Examining Dimethyl Sulfide Emissions in California's San Joaquin Valley

Airborne sampling of aerosol particles: Comparison between surface sampling at Christmas Island and P‐3 sampling during PEM‐Tropics B

Bulk aerosol sampling of soluble ionic compounds from the NASA Wallops Island P‐3 aircraft and a tower on Christmas Island during PEM‐Tropics B provides an opportunity to assess the magnitude of particle losses in the University of New Hampshire airborne bulk aerosol sampling system. We find that most aerosol‐associated ions decrease strongly with height above the sea surface, making direct comparisons between mixing ratios at 30 m on the tower and the lowest flight level of the P‐3 (150 m) open to interpretation. Theoretical considerations suggest that vertical gradients of sea‐salt aerosol particles should show exponential decreases with height. Observed gradients of Na + and Mg 2+ , combining the tower observations with P‐3 samples collected below 1 km, are well described by exponential decreases ( r values of 0.88 and 0.87, respectively), though the curve fit underestimates average mixing ratios at the surface by 25%. Cascade impactor samples collected on the tower show that >99% of the Na + and Mg 2+ mass is on supermicron particles, 65% is in the 1–6 micron range, and just 20% resides on particles with diameters larger than 9 microns. These results indicate that our airborne aerosol sampling probes must be passing particles up to at least 6 microns with high efficiency. We also observed that nss SO 4 2− and NH 4 + , which are dominantly on accumulation mode particles, tended to decrease between 150 and 1000 m, but they were often considerably higher at the lowest P‐3 sampling altitudes than at the tower. This finding is presently not well understood.

Study of Black Sand Particles from Sand Dunes in Badr, Saudi Arabia Using Electron Microscopy

Particulate air pollution is a health concern. This study determines the microscopic make-up of different varieties of sand particles collected at a sand dune site in Badr, Saudi Arabia in 2012. Three categories of sand were studied: black sand, white sand, and volcanic sand. The study used multiple high resolution electron microscopies to study the morphologies, emission source types, size, and elemental composition of the particles, and to evaluate the presence of surface “coatings or contaminants” deposited or transported by the black sand particles. White sand was comprised of natural coarse particles linked to wind-blown releases from crustal surfaces, weathering of igneous/metamorphic rock sources, and volcanic activities. Black sand particles exhibited different morphologies and microstructures (surface roughness) compared with the white sand and volcanic sand. Morphological Scanning Electron Microscopy (SEM) and Laser Scanning Microscopy (LSM) analyses revealed that the black sand contained fine and ultrafine particles (50 to 500 nm ranges) and was strongly magnetic, indicating the mineral magnetite or elemental iron. Aqueous extracts of black sands were acidic (pH = 5.0). Fe, C, O, Ti, Si, V, and S dominated the composition of black sand. Results suggest that carbon and other contaminant fine particles were produced by fossil-fuel combustion and industrial emissions in heavily industrialized areas of Haifa and Yanbu, and transported as cloud condensation nuclei to Douf Mountain. The suite of techniques used in this study has yielded an in-depth characterization of sand particles. Such information will be needed in future environmental, toxicological, epidemiological, and source apportionment studies.