Airborne lidar measurements of ozone above the Los Angeles Basin on 17 July 2009 show orographic lifting of ozone from the surface to the free troposphere by the San Gabriel Mountains. Mixing ratios ...in excess of 100 parts‐per‐billion‐by‐volume (ppbv) were measured ∼4 km above mean sea level (ASL). These observations are in excellent agreement with published model studies, confirming that topographic venting by the so called “mountain chimney effect” is a potentially important pathway for removal of pollutants from the Los Angeles Basin. The lofting of ozone and other pollutants into the free troposphere also greatly increases the potential for long‐range transport from the Basin, and trajectory calculations suggest that some of this ozone may have been transported ∼1000 km to eastern Utah and western Colorado.
We use airborne lidar measurements of ozone collected during the Texas Air Quality Study (TexAQS) 2000 and TexAQS 2006 field campaigns to compute the horizontal flux of ozone downwind of the Houston ...and Dallas/Fort Worth metropolitan areas. Fluxes are computed for each aircraft transect by integrating excess ozone (plume ozone minus background ozone) in the urban plumes and multiplying the result by the horizontal wind speed provided by radar wind profilers. In addition, we use the lidar data to estimate ozone production rates and ozone enhancements in the Houston and Dallas/Fort Worth plumes. We found that the average horizontal flux of ozone emanating from the Houston area based on data from six research flights was 3.2 · 1026 molecules per second. This was significantly higher than the flux measured downwind of Dallas/Fort Worth during a single flight. The Houston fluxes exhibited a strong dependence on wind direction. Under southerly or northerly flow, ozone fluxes were about twice as large as under westerly or easterly flow conditions. We estimate that a day's worth of export of ozone from the Houston area could raise regional background ozone by about 10 ppbv over a 40,000 km2 area. This has important ramifications for air quality in communities downwind of Houston as it could raise background ozone levels enough that regions with little or no local pollution sources of their own may violate the federally mandated ozone standard.
Stratosphere-to-troposphere mass transport to the planetary
boundary layer (STT-PBL) peaks over the western United States during boreal
spring, when deep stratospheric intrusions are most frequent. ...The
tropopause-level jet structure modulates the frequency and character of
intrusions, although the precise relationship between STT-PBL and jet
variability has not been extensively investigated. In this study, we
demonstrate how the North Pacific jet transition from winter to summer leads
to the observed peak in STT-PBL. We show that the transition enhances
STT-PBL through an increase in storm track activity which produces
highly amplified Rossby waves and more frequent deep stratospheric
intrusions over western North America. This dynamic transition coincides
with the gradually deepening PBL, further facilitating STT-PBL in spring. We
find that La Niña conditions in late winter are associated with an
earlier jet transition and enhanced STT-PBL due to deeper and more frequent
tropopause folds. An opposite response is found during El Niño
conditions. El Niño–Southern
Oscillation (ENSO) conditions also influence STT-PBL in late spring or early
summer, during which time La Niña conditions are associated with larger
and more frequent tropopause folds than both El Niño and ENSO-neutral
conditions. These results suggest that knowledge of ENSO state and the North Pacific jet structure in late winter could be leveraged for predicting the
strength of STT-PBL in the following months.
Stratosphere-to-troposphere transport (STT) is an important source of ozone for the troposphere, particularly over western North America. STT in this region is predominantly controlled by a ...combination of the variability and location of the Pacific jet stream and the amount of ozone in the lower stratosphere, two factors which are likely to change if greenhouse gas concentrations continue to increase. Here we use Whole Atmosphere Community Climate Model experiments with a tracer of stratospheric ozone (O3S) to study how end-of-the-century Representative Concentration Pathway (RCP) 8.5 sea surface temperatures (SSTs) and greenhouse gases (GHGs), in isolation and in combination, influence STT of ozone over western North America relative to a preindustrial control background state.
The El Niño-Southern Oscillation (ENSO) is known to modulate the strength and frequency of stratosphere-to-troposphere transport (STT) of ozone over the Pacific-North American region during late ...winter to early summer. Dynamical processes that have been proposed to account for this variability include variations in the amount of ozone in the lowermost stratosphere that is available for STT and tropospheric circulation-related variations in the frequency and geographic distribution of individual STT events.
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.
Abstract
The National Oceanic and Atmospheric Administration/Earth System Research Laboratory/Chemical Sciences Division (NOAA/ESRL/CSD) has developed a versatile, airborne lidar system for measuring ...ozone and aerosols in the boundary layer and lower free troposphere. The Tunable Optical Profiler for Aerosol and Ozone (TOPAZ) lidar was deployed aboard a NOAA Twin Otter aircraft during the Texas Air Quality Study (TexAQS 2006) and the California Research at the Nexus of Air Quality and Climate Change (CalNex 2010) field campaigns. TOPAZ is capable of measuring ozone concentrations in the lower troposphere with uncertainties of several parts per billion by volume at 90-m vertical and 600-m horizontal resolution from an aircraft flying at 60 m s−1. The system also provides uncalibrated aerosol backscatter profiles at 18-m vertical and 600-m horizontal resolution. TOPAZ incorporates state-of-the-art technologies, including a cerium-doped lithium calcium aluminum fluoride (Ce:LiCAF) laser, to make it compact and lightweight with low power consumption. The tunable, three-wavelength UV laser source makes it possible to optimize the wavelengths for differing atmospheric conditions, reduce the interference from other atmospheric constituents, and implement advanced analysis techniques. This paper describes the TOPAZ lidar, its components and performance during testing and field operation, and the data analysis procedure, including a discussion of error sources. The performance characteristics are illustrated through a comparison between TOPAZ and an ozonesonde launched during the TexAQS 2006 field campaign. A more comprehensive set of comparisons with in situ measurements during TexAQS 2006 and an assessment of the TOPAZ accuracy and precision are presented in a companion paper.
On 2019-02-14, at 1:00 UTC, a large increase of ozone density at 8 km altitude was detected above Hampton, Virginia using the NASA Langley Mobile Ozone Lidar, LMOL. Ozone levels above 70 ppbv were ...observed down to an altitude of 4.5 km up to 5 h after the start of the event. The NASA GEOS Composition Forecast (GEOS-CF) model was used to investigate the hypothesis of a stratospheric intrusion (SI). The agreement between the model and the observations confirmed the stratospheric origin of the airmass and highlighted the capabilities of GEOS-CF to simulate intrusions. In parallel, MicroPulse Lidar (MPL) observations indicated that depolarizing particulates high in the troposphere showed downward motions linked to the intrusion. Since these particulates are linked to cirrus clouds, it is hypothesised that the SI led to an ice-virga effect. This might suggest that particulate observations can exhibit patterns of stratospheric intrusions and can be used, in certain cases, as a signature of the events. These particulates, likely ice crystals, have opposite distribution gradients compared to O3 at their interface which could be explained by a non-mixing of stratospheric and tropospheric air-masses as well as destruction of O3 by ice crystal-induced processes. Model-data comparison shows that if that latter effect exists, it has small consequences for the observed case. This work shows the capabilities of the LMOL system to detect SI and to validate the vertical and temporal modeling of SI by GEOS-CF, as well as showing that signatures of SI could be detected by MPL.
•A stratospheric intrusion was observed by O3 lidar and confirmed by modeling.•The intrusion perturbated the ice crystals around cirrus clouds.•The perturbed ice crystals made a signature of the intrusion observable by lidar.•For the First time a stratospheric intrusion was detected by O3 and micropulse lidar.•Several hypotheses remain to explain how the intrusion affected the ice crystals.
The influence of convective mixing on surface ozone in Houston during TexAQS 2006 is examined. We use airborne lidar measurements of ozone and ship‐based Doppler lidar measurements of winds, together ...with ship‐ and ground‐based measurements of surface ozone to characterize horizontal and vertical mixing of ozone plumes from the Houston Ship Channel on two high‐ozone days. We show that a stable capping layer trapped the plume in the boundary layer on 31 August, while shallow convection associated with active fair weather cumulus clouds mixed the plume with free tropospheric air on 17 August. Deep convection associated with an isolated air mass thunderstorm further decreased surface ozone near Galveston Bay in the late afternoon. High ozone thus affected a smaller area for a shorter period on 17 August, despite similar background concentrations and local production. We generalize these findings by comparing Houston ozone concentrations to National Weather Service (Lake Charles, LA) radiosondes. We show that for 1 June to 15 September 2006, stable conditions with high background ozone occurred 18% of the days leading to mean daily 8 h concentrations of 73 ± 11 ppbv. Shallow and deep convection associated with moderate to strongly unstable conditions lowered the mean ozone to 50 ± 11 ppbv (∼29% of days), while weaker convection associated with marginally unstable conditions reduced the mean concentrations to 63 ± 13 ppbv (∼11%). We use these observations to derive simple relationships between surface ozone and convective indicators that may prove useful for parameterization of convective venting in air quality models.
The interannual variability of the springtime maximum in free tropospheric ozone above Colorado is examined using 5‐1/2 years (1993–1998) of Differential Absorption Lidar (DIAL) data. Year‐to‐year ...differences of up to 20% in the monthly mean mixing ratios are shown to be correlated with changes in the 200 hPa wind speed over the eastern Pacific that are associated with the El Niño/Southern Oscillation (ENSO). This correlation is attributed to variations in the intensity of stratosphere‐troposphere exchange (STE) associated with the mean transverse circulation at the subtropical jet exit over the eastern Pacific.
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