The detection and attribution of high background ozone (O3) events in
the southwestern US is challenging but relevant to the effective
implementation of the lowered National Ambient Air Quality ...Standard (NAAQS;
70 ppbv). Here we leverage intensive field measurements from the Fires,
Asian, and Stratospheric Transport−Las Vegas Ozone Study (FAST-LVOS) in
May–June 2017, alongside high-resolution simulations with two global
models (GFDL-AM4 and GEOS-Chem), to study the sources of O3 during
high-O3 events. We show possible stratospheric influence on 4 out of
the 10 events with daily maximum 8 h average (MDA8) surface O3
above 65 ppbv in the greater Las Vegas region. While O3 produced from
regional anthropogenic emissions dominates pollution events in the Las Vegas
Valley, stratospheric intrusions can mix with regional pollution to push
surface O3 above 70 ppbv. GFDL-AM4 captures the key characteristics of
deep stratospheric intrusions consistent with ozonesondes, lidar profiles,
and co-located measurements of O3, CO, and water vapor at Angel Peak,
whereas GEOS-Chem has difficulty simulating the observed features and
underestimates observed O3 by ∼20 ppbv at the surface.
On days when observed MDA8 O3 exceeds 65 ppbv and the AM4 stratospheric
ozone tracer shows 20–40 ppbv enhancements, GEOS-Chem simulates
∼15 ppbv lower US background O3 than GFDL-AM4. The two
models also differ substantially during a wildfire event, with GEOS-Chem
estimating ∼15 ppbv greater O3, in better agreement with
lidar observations. At the surface, the two models bracket the observed MDA8
O3 values during the wildfire event. Both models capture the
large-scale transport of Asian pollution, but neither resolves some
fine-scale pollution plumes, as evidenced by aerosol backscatter, aircraft,
and satellite measurements. US background O3 estimates from the two
models differ by 5 ppbv on average (greater in GFDL-AM4) and up to 15 ppbv
episodically. Uncertainties remain in the quantitative attribution of each
event. Nevertheless, our multi-model approach tied closely to observational
analysis yields some process insights, suggesting that elevated background
O3 may pose challenges to achieving a potentially lower NAAQS level
(e.g., 65 ppbv) in the southwestern US.
A single-particle soot photometer (SP2) was flown on a NASA WB-57F high-altitude research aircraft in November 2004 from Houston, Texas. The SP2 uses laser-induced incandescence to detect individual ...black carbon (BC) particles in an air sample in the mass range of approx.3-300 fg (approx.0.15-0.7 microns volume equivalent diameter). Scattered light is used to size the remaining non-BC aerosols in the range of approx.0.17-0.7 microns diameter. We present profiles of both aerosol types from the boundary layer to the lower stratosphere from two midlatitude flights. Results for total aerosol amounts in the size range detected by the SP2 are in good agreement with typical particle spectrometer measurements in the same region. All ambient incandescing particles were identified as BC because their incandescence properties matched those of laboratory-generated BC aerosol. Approximately 40% of these BC particles showed evidence of internal mixing (e.g., coating). Throughout profiles between 5 and 18.7 km, BC particles were less than a few percent of total aerosol number, and black carbon aerosol (BCA) mass mixing ratio showed a constant gradient with altitude above 5 km. SP2 data was compared to results from the ECHAM4/MADE and LmDzT-INCA global aerosol models. The comparison will help resolve the important systematic differences in model aerosol processes that determine BCA loadings. Further intercomparisons of models and measurements as presented here will improve the accuracy of the radiative forcing contribution from BCA.
The influence of stratosphere‐to‐troposphere transport (STT) on surface ozone (O3) concentrations in the greater Los Angeles area during the CalNex and IONS‐2010 measurement campaigns has been ...investigated. Principal component analysis (PCA) of surface O3measurements from 41 sampling stations indicates that ∼13% of the variance in the maximum daily 8‐h average (MDA8) O3between May 10 and June 19, 2010 was associated with changes of 2–3 day duration linked to the passage of upper‐level troughs. Ozonesondes launched from Joshua Tree National Park and airborne lidar measurements show that these changes coincided with the appearance of stratospheric intrusions in the lower troposphere above southern California. The Lagrangian particle dispersion model FLEXPART reproduces most of these intrusions, and supports the conclusion from the PCA that significant transport of stratospheric air to the surface occurred on May 28–30. This intrusion led to a peak 1‐h O3 concentration of 88 ppbv at Joshua Tree National Monument near the ozonesonde launch site on May 28, and widespread entrainment of stratospheric air into the boundary layer increased the local background O3 over the entire area to ∼55 ppbv on May 29–30. This background was 10–15 ppbv higher than the baseline O3 in air transported ashore from the Pacific Ocean, and when combined with locally produced O3 led to several exceedances of the current National Ambient Air Quality Standard (NAAQS) on the following day.
Key Points
Stratosphere‐troposphere transport can influence surface ozone
Background ozone must be considered in urban areas
Transport cannot be neglected in air quality studies
Scientists working with large volumes of high-dimensional data, such as global climate patterns, stellar spectra, or human gene distributions, regularly confront the problem of dimensionality ...reduction: finding meaningful low-dimensional structures hidden in their high-dimensional observations. The human brain confronts the same problem in everyday perception, extracting from its high-dimensional sensory inputs-30,000 auditory nerve fibers or 106optic nerve fibers-a manageably small number of perceptually relevant features. Here we describe an approach to solving dimensionality reduction problems that uses easily measured local metric information to learn the underlying global geometry of a data set. Unlike classical techniques such as principal component analysis (PCA) and multidimensional scaling (MDS), our approach is capable of discovering the nonlinear degrees of freedom that underlie complex natural observations, such as human handwriting or images of a face under different viewing conditions. In contrast to previous algorithms for nonlinear dimensionality reduction, ours efficiently computes a globally optimal solution, and, for an important class of data manifolds, is guaranteed to converge asymptotically to the true structure.
The Fires, Asian, and Stratospheric Transport–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 May–30 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 (≈ 900 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. (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 % (35 of 45) of the sample days and show that entrainment of these layers contributed to mean 8 h average regional
background O3 concentrations of 50–55 parts per billion by volume
(ppbv), or about 85–95 µg m−3. These high background
concentrations constitute 70 %–80 % of the current US National Ambient Air Quality Standard (NAAQS) of 70 ppbv (≈ 120 µg m−3 at 900 m a.s.l.) for the daily maximum 8 h average (MDA8) and will make attainment of the more stringent standards of 60 or 65 ppbv currently being considered
extremely difficult in the interior SWUS.
This Letter reports a measurement of the flux and energy spectrum of electron antineutrinos from six 2.9 GWth nuclear reactors with six detectors deployed in two near (effective baselines 512 and 561 ...m) and one far (1579 m) underground experimental halls in the Daya Bay experiment. Using 217 days of data, 296 721 and 41 589 inverse β decay (IBD) candidates were detected in the near and far halls, respectively. The measured IBD yield is (1.55±0.04) ×10(-18) cm(2) GW(-1) day(-1) or (5.92±0.14) ×10(-43) cm(2) fission(-1). This flux measurement is consistent with previous short-baseline reactor antineutrino experiments and is 0.946±0.022 (0.991±0.023) relative to the flux predicted with the Huber-Mueller (ILL-Vogel) fissile antineutrino model. The measured IBD positron energy spectrum deviates from both spectral predictions by more than 2σ over the full energy range with a local significance of up to ∼4σ between 4-6 MeV. A reactor antineutrino spectrum of IBD reactions is extracted from the measured positron energy spectrum for model-independent predictions.
A series of deep stratospheric intrusions in late May 2013 increased the daily maximum 8 h surface ozone (O3) concentrations to more than 70 parts per billion by volume (ppbv) at rural and urban ...surface monitors in California and Nevada. This influx of ozone‐rich lower stratospheric air and entrained Asian pollution persisted for more than 5 days and contributed to exceedances of the 2008 8 h national ambient air quality standard of 75 ppbv on 21 and 25 May in Clark County, NV. Exceedances would also have occurred on 22 and 23 May had the new standard of 70 ppbv been in effect. In this paper, we examine this episode using lidar measurements from a high‐elevation site on Angel Peak, NV, and surface measurements from NOAA, the Clark County, Nevada Department of Air Quality, the Environmental Protection Agency Air Quality System, and the Nevada Rural Ozone Initiative. These measurements, together with analyses from the National Centers for Environmental Prediction/North American Regional Reanalysis; NOAA Geophysical Fluid Dynamics Laboratory AM3 model; NOAA National Environmental Satellite, Data, and Information Service Real‐time Air Quality Modeling System; and FLEXPART models, show that the exceedances followed entrainment of ~20 to 40 ppbv of lower stratospheric ozone mingled with another 0 to 10 ppbv of ozone transported from Asia by the unusually deep convective boundary layers above the Mojave desert. Our analysis suggests that this vigorous mixing can affect both high and low elevations and help explain the springtime ozone maximum in the southwestern U.S.
Plain Language Summary
Ozone (O3) is formed high in the upper atmosphere when ultraviolet (UV) rays from the sun break the bond in molecular oxygen (O2). This so‐called "good" ozone protects plants and animals at the ground from the damaging effects of these UV rays. Ozone is also formed in the lower atmosphere through reactions between nitrogen oxides (NOx) and volatile organic compounds (VOCs) of natural and human origin. This "bad" ozone can damage the sensitive tissues of plants and animals. The U.S. Clean Air Act (CAA) established standards designed to keep the ozone in the air we breathe at healthy levels by regulating NOx and VOC precursors emitted by human activities. The standard is revised periodically as new data on the health effects of ozone become available, and the current standard is close to the normal background levels found in some parts of the U.S. during springtime. This means that the concentrations can sometimes exceed the standard when storms bring "good" ozone from the upper atmosphere down to the ground where it becomes "bad" ozone. We take a look at this process and discuss why it is more likely to happen in the Southwest than in other parts of the U.S.
Key Points
The deep convective boundary layers of the Southwestern U.S. increase entrainment of stratospheric air and transported pollution
Stratospheric intrusions contribute to the springtime surface ozone maximum in the Southwestern U.S.
Stratospheric intrusions can cause exceedances of the National Ambient Air Quality Standard for ozone in the Southwestern U.S.
The California Research at the Nexus of Air Quality and Climate Change (CalNex) field study was conducted throughout California in May, June, and July of 2010. The study was organized to address ...issues simultaneously relevant to atmospheric pollution and climate change, including (1) emission inventory assessment, (2) atmospheric transport and dispersion, (3) atmospheric chemical processing, and (4) cloud‐aerosol interactions and aerosol radiative effects. Measurements from networks of ground sites, a research ship, tall towers, balloon‐borne ozonesondes, multiple aircraft, and satellites provided in situ and remotely sensed data on trace pollutant and greenhouse gas concentrations, aerosol chemical composition and microphysical properties, cloud microphysics, and meteorological parameters. This overview report provides operational information for the variety of sites, platforms, and measurements, their joint deployment strategy, and summarizes findings that have resulted from the collaborative analyses of the CalNex field study. Climate‐relevant findings from CalNex include that leakage from natural gas infrastructure may account for the excess of observed methane over emission estimates in Los Angeles. Air‐quality relevant findings include the following: mobile fleet VOC significantly declines, and NOx emissions continue to have an impact on ozone in the Los Angeles basin; the relative contributions of diesel and gasoline emission to secondary organic aerosol are not fully understood; and nighttime NO3 chemistry contributes significantly to secondary organic aerosol mass in the San Joaquin Valley. Findings simultaneously relevant to climate and air quality include the following: marine vessel emissions changes due to fuel sulfur and speed controls result in a net warming effect but have substantial positive impacts on local air quality.
Key Points
An overview of the multi‐platform, multi‐agency CalNex field study in 2010
A synthesis of CalNex research to date
Emphasis on policy‐relevant conclusions linking climate and air quality issues
A high precision calibration of the nonlinearity in the energy response of the Daya Bay Reactor Neutrino Experiment’s antineutrino detectors is presented in detail. The energy nonlinearity originates ...from the particle-dependent light yield of the scintillator and charge-dependent electronics response. The nonlinearity model is constrained by γ calibration points from deployed and naturally occurring radioactive sources, the β spectrum from 12B decays, and a direct measurement of the electronics nonlinearity with a new flash analog-to-digital converter readout system. Less than 0.5% uncertainty in the energy nonlinearity calibration is achieved for positrons of kinetic energies greater than 1 MeV.
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