Measurements of aerosol particle size distributions and composition and of trace and reactive gas mixing ratios were made on the NOAA WP‐3D aircraft downwind of mixed urban/industrial sources in the ...northeastern United States (U.S.). These measurements were made in noncloudy air during July and August 2004, under conditions where cloud processing was not likely to play an important role in oxidation chemistry. Under these conditions, particulate sulfate was found to be produced with an exponential time constant of ∼3.5 d from the gas‐phase oxidation of SO2, which was ubiquitous but inhomogeneously distributed in the pollution plumes. When submicron particle mass concentrations exceeded 15 μg m−3, sulfate and associated ammonium dominated the composition; at lower mass concentrations particulate organic matter (OM) dominated. Since most of the urban plumes sampled contained substantial SO2 from nearby industrial sources, the apportionment of aerosol mass between OM and sulfate compounds under noncloudy conditions was governed largely by the differences between the oxidation timescales of SO2 and those of precursor volatile organic compounds (VOCs) relative to their transport time. These differences in oxidation timescales may explain much of the variability in previously published OM/sulfate ratios for this region. These observations indicate that even with higher‐than‐expected secondary OM formation, in the northeastern U.S. the potential inorganic particulate mass from SO2 emissions significantly exceeds the potential secondary OM from anthropogenic VOC emissions.
Measurements were made on board the NOAA RV Ronald H. Brown during the second New England Air Quality Study (NEAQS 2004) to determine the source of the aerosol in the region and how sources and aging ...processes affect submicrometer aerosol chemical composition and optical properties. Using the Lagrangian particle dispersion model FLEXPART in combination with gas phase tracer compounds, local (urban), regional (NE U.S. urban corridor of Washington, D.C.; New York; and Boston), and distant (midwest industries and North American forest fires) sources were identified. Submicrometer aerosol measured near the source region (Boston Harbor) had a molar equivalence ratio near one with respect to NH4+, NO3−, and SO4=, had a large mass fraction of particulate organic matter (POM) relative to SO4=, and had relatively unoxidized POM. As distance from the source region increased, the submicrometer aerosol measured in the marine boundary layer became more acidic and had a lower POM mass fraction, and the POM became more oxidized. The relative humidity dependence of light extinction reflected the change in aerosol composition being lower for the near‐source aerosol and higher for the more processed aerosol. A factor analysis performed on a combined data set of aerosol and gas phase parameters showed that the POM measured during the experiment was predominantly of secondary anthropogenic origin.
Nitrogen oxides (NOx) are air pollutants critical to ozone and fine particle production in the troposphere. Here, we present fuel‐based emission inventories updated to 2018, including for mobile ...source engines using the Fuel‐based Inventory of Vehicle Emissions (FIVEs) and oil and gas production using the Fuel‐based Oil and Gas (FOG) inventory. The updated FIVE emissions are now consistent with the NEI17 estimates differing within 2% across the contiguous US (CONUS). Tropospheric NO2 columns modeled by the Weather Research and Forecasting with Chemistry model (WRF‐Chem) are compared with those observed by TROPOspheric Monitoring Instrument (TROPOMI) and Ozone Monitoring Instrument (OMI) during the summer of 2018. Modeled NO2 columns show strong temporal and spatial correlations with TROPOMI (OMI), identified with biases of −3% (−21%) over CONUS, and +8% (−6%) over point sources plus urban regions. Taking account of the negative bias (∼20%) in early version of TROPOMI over polluted regions, WRF‐Chem shows good performance with updated FIVE and FOG emissions. Our model tends to under‐predict the tropospheric NO2 columns over background and rural regions (bias of −21% to −3%). Through model sensitivity analyses, we demonstrate the important roles of emissions from soils (11.7% average over CONUS), oil and gas production (4.1%), wildfires (10.6%), and lightning (2.3%) with greater contributions at regional scales. This work provides a roadmap for satellite‐based evaluations for emission updates from various sources.
Plain Language Summary
Satellite observations of tropospheric NO2 columns provide important constraints on air pollutants from space, which have been widely used to validate the performance of atmospheric models. To gain better knowledge of the accuracy of the recently updated fuel‐based emissions inventory, we conducted NO2 assessments between a regional chemical transport model (Weather Research and Forecasting with Chemistry model, WRF‐Chem), with the TROPOspheric Monitoring Instrument (TROPOMI) and Ozone Monitoring Instrument (OMI) over the contiguous United States. We find that model simulation results show strong spatial and temporal correlations with satellite observations across point sources, urban, oil and gas production, and rural regions. With updated emissions, our regional atmospheric model can reconcile with satellite retrievals differing from −3% (TROPOMI) to −21% (OMI) overall. Soils, oil and gas production, wildfires and lightning emissions can play key roles in regional air quality. This work provides an important baseline of a pre‐COVID year by which sharp changes in anthropogenic NOx emissions due to the pandemic can be assessed.
Key Points
Updated fuel‐based NOx emissions for 2018 are now consistent with the NEI 2017 within 2% for mobile source engines across the contiguous US
WRF‐Chem reproduces trop. NO2 columns over point plus urban regions within 10% but underestimates in remote area by −21%(OMI) to −3%(TROPOMI)
Sensitivity analyses show important roles of soil (11.7%), fire (10.6%), O&G (4.1%), lightning (2.3%) over CONUS, especially at regional scales
Here we analyze regional-scale data collected on board the NOAA WP-3D aircraft during the 2013 Southeast Nexus (SENEX) campaign to study the aerosol–cloud droplet link and quantify the sensitivity of ...droplet number to aerosol number, chemical composition, and vertical velocity. For this, the observed aerosol size distributions, chemical composition, and vertical-velocity distribution are introduced into a state-of-the-art cloud droplet parameterization to show that cloud maximum supersaturations in the region range from 0.02 % to 0.52 %, with an average of 0.14±0.05 %. Based on these low values of supersaturation, the majority of activated droplets correspond to particles with a dry diameter of 90 nm and above. An important finding is that the standard deviation of the vertical velocity (σw) exhibits considerable diurnal variability (ranging from 0.16 m s−1 during nighttime to over 1.2 m s−1 during day), and it tends to covary with total aerosol number (Na). This σw–Na covariance amplifies the predicted response in cloud droplet number (Nd) to Na increases by 3 to 5 times compared to expectations based on Na changes alone. This amplified response is important given that droplet formation is often velocity-limited and therefore should normally be insensitive to aerosol changes. We also find that Nd cannot exceed a characteristic concentration that depends solely on σw. Correct consideration of σw and its covariance with time and Na is important for fully understanding aerosol–cloud interactions and the magnitude of the aerosol indirect effect. Given that model assessments of aerosol–cloud–climate interactions do not routinely evaluate for overall turbulence or its covariance with other parameters, datasets and analyses such as the one presented here are of the highest priority to address unresolved sources of hydrometeor variability, bias, and the response of droplet number to aerosol perturbations.
In June 2010, the NOAA WP-3D aircraft conducted two survey flights around the Deepwater Horizon (DWH) oil spill. The Gulf oil spill resulted in an isolated source of secondary organic aerosol (SOA) ...precursors in a relatively clean environment. Measurements of aerosol composition and volatile organic species (VOCs) indicated formation of SOA from intermediate-volatility organic compounds (IVOCs) downwind of the oil spill (Science 2011, 331, doi 10.1126/science.1200320). In an effort to better understand formation of SOA in this environment, we present mass spectral characteristics of SOA in the Gulf and of SOA formed in the laboratory from evaporated light crude oil. Compared to urban primary organic aerosol, high-mass-resolution analysis of the background-subtracted SOA spectra in the Gulf (for short, “Gulf SOA”) showed higher contribution of C x H y O+ relative to C x H y + fragments at the same nominal mass. In each transect downwind of the DWH spill site, a gradient in the degree of oxidation of the Gulf SOA was observed: more oxidized SOA (oxygen/carbon = O/C ∼0.4) was observed in the area impacted by fresher oil; less oxidized SOA (O/C ∼0.3), with contribution from fragments with a hydrocarbon backbone, was found in a broader region of more-aged surface oil. Furthermore, in the plumes originating from the more-aged oil, contribution of oxygenated fragments to SOA decreased with downwind distance. Despite differences between experimental conditions in the laboratory and the ambient environment, mass spectra of SOA formed from gas-phase oxidation of crude oil by OH radicals in a smog chamber and a flow tube reactor strongly resembled the mass spectra of Gulf SOA (r 2 > 0.94). Processes that led to the observed Gulf SOA characteristics are also likely to occur in polluted regions where VOCs and IVOCs are coemitted.
Airborne measurements of aerosol composition and gas phase compounds over the Deepwater Horizon (DWH) oil spill in the Gulf of Mexico in June 2010 indicated the presence of high concentrations of ...secondary organic aerosol (SOA) formed from organic compounds of intermediate volatility. In this work, we investigated SOA formation from South Louisiana crude oil vapors reacting with OH in a Potential Aerosol Mass flow reactor. We use the dependence of evaporation time on the saturation concentration (C*) of the SOA precursors to separate the contribution of species of different C* to total SOA formation. This study shows consistent results with those at the DWH oil spill: (1) organic compounds of intermediate volatility with C* = 105–106 μg m–3 contribute the large majority of SOA mass formed, and have much larger SOA yields (0.37 for C* = 105 and 0.21 for C* = 106 μg m–3) than more volatile compounds with C*≥107 μg m–3, (2) the mass spectral signature of SOA formed from oxidation of the less volatile compounds in the reactor shows good agreement with that of SOA formed at DWH oil spill. These results also support the use of flow reactors simulating atmospheric SOA formation and aging.
Organic compounds were measured by proton transfer reaction‐mass spectrometry (PTR‐MS) on board the National Oceanic and Atmospheric Administration's research ship Ronald H. Brown during the New ...England Air Quality Study (NEAQS) in July and August of 2002. PTR‐MS has the potential to measure many important organic species with a fast time response, but its validity has not been proven sufficiently. The results obtained by PTR‐MS during NEAQS were compared with those from (oxygenated) hydrocarbon measurements by gas chromatography/mass spectrometry (GC‐MS), peroxyacyl nitrate measurements by gas chromatography/electron capture detection, and carboxylic acid measurements by mist chamber/ion chromatography. The PTR‐MS and GC‐MS data for methanol, acetonitrile, acetone, isoprene, benzene, and toluene agreed within the measurement uncertainties. The comparison for C8 aromatics and acetaldehyde was less quantitative due to calibration inaccuracies. In addition, PTR‐MS measured the sum of methyl vinyl ketone and methacrolein at 71 amu, the sum of C9 aromatics at 121 amu, and the sum of monoterpenes at 81 and 137 amu. The PTR‐MS signal at 61 amu was found to correlate well with data for acetic acid. The signal at 73 amu correlated reasonably well with methyl ethyl ketone data, but the quantitative disagreement suggested interference from other species, possibly methyl glyoxal. The signal at 77 amu correlated well with data for peroxyacetyl nitrate, and the sensitivity inferred from the field data agreed within 30% with the results from laboratory calibrations. Finally, the signal at 105 amu was attributed to styrene and peroxy isobutyryl nitrate. These results prove that many important organic species can be measured accurately and with a fast response time by PTR‐MS.
During the NOAA Southern Oxidant Study 1999 (SOS1999), Texas Air Quality Study 2000 (TexAQS2000), International Consortium for Atmospheric Research on Transport and Transformation (ICARTT2004), and ...Texas Air Quality Study 2006 (TexAQS2006) campaigns, airborne measurements of isoprene and monoterpenes were made in the eastern United States and in Texas, and the results are used to evaluate the biogenic emission inventories BEIS3.12, BEIS3.13, MEGAN2, and WM2001. Two methods are used for the evaluation. First, the emissions are directly estimated from the ambient isoprene and monoterpene measurements assuming a well‐mixed boundary layer and are compared with the emissions from the inventories extracted along the flight tracks. Second, BEIS3.12 is incorporated into the detailed transport model FLEXPART, which allows the isoprene and monoterpene mixing ratios to be calculated and compared to the measurements. The overall agreement for all inventories is within a factor of 2 and the two methods give consistent results. MEGAN2 is in most cases higher, and BEIS3.12 and BEIS3.13 lower than the emissions determined from the measurements. Regions with clear discrepancies are identified. For example, an isoprene hot spot to the northwest of Houston, Texas, was expected from BEIS3 but not observed in the measurements. Interannual differences in emissions of about a factor of 2 were observed in Texas between 2000 and 2006.
Emissions of methane (CH4) in the Permian basin (USA) have been derived for 2019 and 2020 from satellite observations of the Tropospheric Monitoring Instrument (TROPOMI) using the divergence method, ...in combination with a data driven method to estimate the background column densities. The resulting CH4 emission data, which have been verified using model data with known emissions, have a spatial resolution of approximately 10 km. The CH4 emissions show moderate spatial correlation with the locations of oil and gas production and drilling activities in the Permian basin, as well as with emissions of nitrogen oxides (NOx). Analysis of the emission maps and time series indicates that a significant fraction of methane emissions in the Permian basin is from frequent widespread emissions sources, rather than from a few infrequent very large unplanned releases, which is important considering possible CH4 emission mitigation strategies. In addition to providing spatially resolved emissions, the divergence method also provides the total emissions of the Permian basin and its main sub‐basins. The total CH4 emission of the Permian is estimated as 3.0 ± 0.7 Tg yr−1 for 2019, which agrees with other independent estimates based on TROPOMI data. For the Delaware sub‐basin, it is estimated as 1.4 ± 0.3 Tg yr−1 for 2019, and for the Midland sub‐basin 1.2 ± 0.3 Tg yr−1. In 2020 the emissions are 9% lower compared to 2019 in the entire Permian basin, and respectively 19% and 27% for the Delaware and Midland sub‐basins.
Plain Language Summary
Methane is a strong greenhouse gas that contributes to climate change. To be able to mitigate methane emissions, it is important to know the main sources and to monitor if reduction measures work. In this study, we estimated the emissions from the oil and gas industry using satellite observations in the Permian basin in the USA, a region with thousands of wells. We have derived maps of the emissions in this region with a spatial resolution of 10 km, which show enhanced emissions in the main oil and gas production regions. The results indicate that frequent widespread emissions significantly contribute to the methane emissions in the Permian basin. In addition, we were able to estimate annual emissions from the basin, which correspond well with other studies.
Key Points
Methane emissions from the Permian basin in the USA can be derived from satellite data with a spatial resolution of approximately 10 km
The derived emissions are spatially moderately correlated with satellite‐derived NOx emissions and oil and gas industry activities
A significant fraction of methane emissions in the Permian basin is from frequent widespread emissions sources related to the oil and gas industry
The Houston‐Galveston‐Brazoria urban area contains industrial petrochemical sources that emit volatile organic compounds and nitrogen oxides, resulting in rapid and efficient ozone production ...downwind. During September to October 2006, the NOAA WP‐3D aircraft conducted research flights as part of the second Texas Air Quality Study (TexAQS II). We use measurements of NOx, SO2, and speciated hydrocarbons from industrial sources in Houston to derive source emission ratios and compare these to emission inventories and the first Texas Air Quality Study (TexAQS) in 2000. Between 2000 and 2006, NOx/CO2 emission ratios changed by an average of −29% ± 20%, while a significant trend in SO2/CO2 emission ratios was not observed. We find that high hydrocarbon emissions are routine for the isolated petrochemical facilities. Ethene (C2H4) and propene (C3H6) are the major contributors to ozone formation based on calculations of OH reactivity for organic species including C2–C10 alkanes, C2–C5 alkenes, ethyne, and C2–C5 aldehydes and ketones. Measured ratios of C2H4/NOx and C3H6/NOx exceed emission inventory values by factors of 1.4–20 and 1–24, respectively. We examine trends in C2H4/NOx and C3H6/NOx ratios between 2000 and 2006 for the isolated petrochemical sources and estimate a change of −30% ± 30%, with significant day‐to‐day and within‐plume variability. Median ambient mixing ratios of ethene and propene in Houston show decreases of −52% and −48%, respectively, between 2000 and 2006. The formaldehyde, acetaldehyde, and peroxyacetyl nitrate products produced by alkene oxidation are observed downwind, and their time evolution is consistent with the rapid photochemistry that also produces ozone.
PDF
