Abstract The 2019 Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) field experiment obtained a diverse set of in situ and remotely sensed measurements before and during a ...pyrocumulonimbus (pyroCb) event over the Williams Flats fire in Washington State. This unique dataset confirms that pyroCb activity is an efficient vertical smoke transport pathway into the upper troposphere and lower stratosphere (UTLS). The magnitude of smoke plumes observed in the UTLS has increased significantly in recent years, following unprecedented wildfire and pyroCb activity observed worldwide. The FIREX-AQ pyroCb dataset is therefore extremely relevant to a broad community, providing the first measurements of fresh smoke exhaust in the upper troposphere, including from within active pyroCb cloud tops. High-resolution remote sensing reveals that three plume cores linked to localized fire fronts, burning primarily in dense forest fuels, contributed to four total pyroCb “pulses.” Rapid changes in fire geometry and spatial extent dramatically influenced the magnitude, behavior, and duration of pyroCb activity. Cloud probe measurements and weather radar identify the presence of large ice particles within the pyroCb and hydrometers below cloud base, indicating precipitation development. The resulting feedbacks suggest that vertical smoke transport efficiency was reduced slightly when compared with intense pyroCb events reaching the lower stratosphere. Physical and optical aerosol property measurements in pyroCb exhaust are compared with previous assumptions. A large suite of aerosol and gas-phase chemistry measurements sets a foundation for future studies aimed at understanding the composition of smoke plumes lifted by pyroconvection into the UTLS and their role in the climate system.
NOx emissions and O3 chemistry in the Los Angeles (L.A.) Basin during the CalNex-2010 field campaign (May–June 2010) have been evaluated by analyzing O3 and NOy (NO, NO2, HNO3, PAN) observations ...using a regional air quality model (WRF-Chem). Model simulations were conducted at 4-km spatial resolution over the basin using the Carbon-Bond Mechanism version Z (CBM-Z) and NOx emissions reduced by 24% relative to 2005 National Emissions Inventory (NEI’05), according to recent state emission statistics (BASE_NOx scenario). In addition, a 22–26% NOx emission reduction from weekday to weekend was applied. WRF-Chem reproduced the observed diurnal cycle and day-to-day variations in surface O3, Ox, HNO3 and HCHO (correlation r2 = 0.57 − 0.63; pairs of data n > 400; confidence value p < 0.01) at the CalNex supersite at Caltech but consistently overestimated surface NO and NO2. A 45% reduction of NOx emissions relative to NEI’05 (LOW_NOx scenario), as suggested by the OMI-NO2 column trend in California over the same period, improved the agreement of modeled NO2, NOx, and O3 with observations on weekdays. Three-dimensional distributions of daytime O3 and NOy were compared with five daytime NOAA WP-3D flights (three on weekdays and two on weekends) to study the Weekend-to-Weekday (WE-to-WD) effects by using the LOW_NOx scenario. Aircraft data showed a 17.3 ppb O3 increase and a 54% NOy reduction in the boundary layer on weekends relative to weekdays, while modeled WE-to-WD differences were much smaller, with a 2.9 ppb O3 increase and 16% NOy reduction only. Model results on weekends underestimated O3 by 23% and overestimated NOy and HNO3 by 40% and 27%, respectively, which may indicate that weekend NOx emissions (45% reduction relative to NEI’05 with a 22–26% reduction on weekends compared to weekdays) were still overestimated in the model. Comparisons of PAN to HNO3 ratios also indicated that the enhanced photochemistry on weekends was not well represented in the model. Although modeled weekday O3 was close to the observations in the boundary layer, modeled PAN and HNO3 were overestimated by 30% and 22%, respectively, and modeled NOy was underestimated by 24% on weekdays. Interpreted as emission ratios, the slopes of volatile organic compound (VOC) species versus CO concentrations indicated that speciated VOC emissions in the model were not accurately represented, impacting the photochemistry in the model. These findings argue for the need to improve our understanding of VOC emissions and their photochemical processing in the model.
•NOx emissions and O3 chemistry in the Los Angeles Basin are evaluated.•NOx is overestimated in the baseline scenario (24% reduction relative to NEI’05).•A 45% reduction of NOx emissions relative to NEI’05 significantly improves the comparison of model to observations.•Modeled Weekend–Weekday differences are much smaller, indicating weekend NOx emissions are still overestimated.•Improved understanding of volatile organic compound emissions and photochemical processing on weekdays are needed.
National ambient air quality standards (NAAQS) have been set for PM2.5 due to its association with adverse health effects. PM2.5 design values in the South Coast Air Basin (SoCAB) and San Joaquin ...Valley of California exceed NAAQS levels, and NH4+ and NO3− make up the largest fraction of total PM2.5 mass on polluted days. Here we evaluate fine‐scale simulations of PM2.5 NH4+ and NO3− with the Community Multiscale Air Quality model using measurements from routine networks and the California Research at the Nexus of Air Quality and Climate Change 2010 campaign. The model correctly simulates broad spatial patterns of NH4+ and NO3− including the elevated concentrations in eastern SoCAB. However, areas for model improvement have been identified. NH3 emissions from livestock and dairy facilities appear to be too low, while those related to waste disposal in western SoCAB may be too high. Analyses using measurements from flights over SoCAB suggest that problems with NH3 predictions can influence NO3− predictions there. Offline ISORROPIA II calculations suggest that overpredictions of NHx in Pasadena cause excessive partitioning of total nitrate to the particle phase overnight, while underpredictions of Na+ cause too much partitioning to the gas phase during the day. Also, the model seems to underestimate mixing during the evening boundary layer transition leading to excessive nitrate formation on some nights. Overall, the analyses demonstrate fine‐scale variations in model performance within and across the air basins. Improvements in inventories and spatial allocations of NH3 emissions and in parameterizations of sea spray emissions, evening mixing processes, and heterogeneous ClNO2 chemistry could improve model performance.
Key Points
Broad spatial patterns of 24 h average nitrate are simulated well
Underprediction of sodium limits partitioning of nitrate to particles in LA
Nocturnal nitrate production is impacted by modeling of evening PBL transition
Understanding how steroid hormones regulate physiological functions has been significantly advanced by structural biology approaches. However, progress has been hampered by significant misfolding of ...the ligand binding domains in heterologous expression systems and by conformational flexibility that interferes with crystallization. Here, we show that protein folding problems common to steroid hormone receptors are circumvented by a mutations that stabilize well-characterized conformations of the receptor. We use this approach to present the first structure of an apo steroid receptor, revealing a ligand-accessible channel, allowing soaking of preformed crystals. Furthermore, crystallization of different pharmacological classes of compounds allowed us to define the structural basis of NFκB selective signaling through ER, revealing a unique conformation of the receptor that allows selective suppression of inflammatory gene expression. The ability to crystallize many receptor-ligand complexes with distinct pharmacophores allows one to define the structural features of signaling specificity that would not be apparent in a single structure.
Summertime aerosol optical extinction (βext) was measured in the Colorado Front Range and Denver metropolitan area as part of the Front Range Air Pollution and Photochemistry Éxperiment (FRAPPÉ) ...campaign during July–August 2014. An Aerodyne cavity attenuated phase shift particle light extinction monitor (CAPS-PMex) was deployed to measure βext (at average relative humidity of 20 ± 7 %) of submicron aerosols at λ = 632 nm at 1 Hz. Data from a suite of gas-phase instrumentation were used to interpret βext behavior in various categories of air masses and sources. Extinction enhancement ratios relative to CO (Δβext ∕ ΔCO) were higher in aged urban air masses compared to fresh air masses by ∼ 50 %. The resulting increase in Δβext ∕ ΔCO for highly aged air masses was accompanied by formation of secondary organic aerosols (SOAs). In addition, the impacts of aerosol composition on βext in air masses under the influence of urban, natural oil and gas operations (O&G), and agriculture and livestock operations were evaluated. Estimated non-refractory mass extinction efficiency (MEE) values for different air mass types ranged from 1.51 to 2.27 m2 g−1, with the minimum and maximum values observed in urban and agriculture-influenced air masses, respectively. The mass distribution for organic, nitrate, and sulfate aerosols presented distinct profiles in different air mass types. During 11–12 August, regional influence of a biomass burning event was observed, increasing the background βext and estimated MEE values in the Front Range.
Satellite ammonia (NH3) observations provide unprecedented insights into NH3 emissions, spatiotemporal variabilities and trends, but validation with in situ measurements remains lacking. Here, total ...columns from the Infrared Atmospheric Sounding Interferometer (IASI) were intercompared to boundary layer NH3 profiles derived from aircraft- and surface-based measurements primarily in Colorado, USA, in the summer of 2014. IASI-NH3 version 3 near real-time data set compared well to in situ derived columns (windows ±15 km around centroid, ±1 h around overpass time) with a correlation of 0.58, a slope of 0.78 ± 0.14 and an intercept of 2.1 × 1015±1.5 × 1015 molecules cm−2. Agreement degrades at larger spatiotemporal windows, consistent with the short atmospheric lifetime of NH3. We also examined IASI version 3R data, which relies on temperature retrievals from the ERA Reanalysis, and a third product generated using aircraft-measured temperature profiles. The overall agreement improves slightly for both cases, and neither is biased within their combined measurement errors. Thus, spatiotemporal averaging of IASI over large windows can be used to reduce retrieval noise. Nonetheless, sampling artifacts of airborne NH3 instruments result in significant uncertainties of the in situ-derived columns. For example, large validation differences exist between ascent and descent profiles, and the assumptions of the free tropospheric NH3 profiles used above the aircraft ceiling significantly impact the validation. Because short-lived species like NH3 largely reside within the boundary layer with complex vertical structures, more comprehensive validation is needed across a wide range of environments. More accurate and widespread in situ NH3 data sets are therefore required for improved validations of satellite products.
Volcanic emissions can significantly affect the Earth's radiation budget by emitting aerosol particles and gas‐phase species that can result in the new particle formation (NPF). These particles can ...scatter solar radiation or modify cloud properties, with consequences on health, weather, and climate. To our knowledge, this is the first dedicated study detailing how gas‐phase precursors emitted from volcanic plumes can influence the NPF. A series of airborne measurements were performed around the Etna and Stromboli volcanoes within the framework of the CLerVolc and STRAP projects. The ATR‐42 aircraft was equipped with a range of instrumentation allowing the measurement of particle number concentration in diameter range above 2.5 nm and gaseous species to investigate the aerosol dynamics and the processes governing the NPF and their growth within the volcanic plumes. We demonstrate that NPF occurs within the volcanic plumes in the free troposphere (FT) and boundary layer (BL). Typically, the NPF events were more pronounced in the FT, where the condensational sink was up to two orders of magnitude smaller and the temperature was ~20 °C lower than in the BL. Within the passive volcanic plume, the concentration of sulfur dioxide, sulfuric acid, and N2.5 were as high as 92 ppbV, 5.65 × 108 and 2.4 × 105 cm−3, respectively. Using these measurements, we propose a new parameterization for NPF rate (J2.5) within the passive volcanic plume in the FT. These results can be incorporated into mesoscale models to better assess the impact of the particle formed by natural processes, that is, volcanic plumes, on climate.
Key Points
New particle formation was evidenced to occur within different volcanic plumes of Etna and Stromboli and was more pronounced in the free troposphere
The growth of the newly formed particles to the CCN active size was observed to occur within the volcanic plumes in different rates
A novel parameterization rate of new particle formation within the Etna's volcanic passive plume was proposed based on the actual measurements
The San Joaquin Valley (SJV) of California has one of the nation's most severe wintertime PM2.5 pollution problems. The DISCOVER-AQ (Deriving Information on Surface Conditions from Column and ...Vertically Resolved Observations Relevant to Air Quality) field campaign took place in the SJV from January 16 to February 6, 2013. It captured two PM2.5 pollution episodes with peak 24-h concentrations approaching 70 μg/m3. Using meteorological fields generated from WRFv3.6, CMAQv5.0.2 was applied to simulate PM2.5 formation in the SJV from January 10 through February 10, 2013. Overall, the model was able to capture the observed accumulation of PM2.5 within the simulation period. The model was able to produce increased concentrations of ammonium nitrate and organic carbon, which are two major components of wintertime PM2.5 in the SJV. Comparison to measurements made by aircraft showed that there was general agreement between observed and modeled daytime vertical distributions of selected gas and particulate species, reflecting the adequacy of modeled daytime mixing layer heights. Excess ammonia predicted by the model implied that ammonium nitrate formation was limited by the availability of nitric acid, consistent with observations. Evaluation of the ammonium nitrate diurnal profile revealed that the observed morning increase of ammonium nitrate was also evident from the model. This paper demonstrates that the CMAQ model is able to simulate elevated wintertime PM2.5 formation observed in the SJV during the DISCOVER-AQ 2013 period, which featured both climatic (i.e., 2011–2014 California Drought) and emissions differences compared to a previous large air quality field campaign in the SJV during 1999–2000.
•A field campaign DISCOVER-AQ took place in the SJV during Jan–Feb 2013•Ammonium nitrate and organic carbon are the two key PM2.5 components.•Ammonium nitrate formation is limited by the availability of nitric acid.•CMAQ captured the accumulation of elevated PM2.5 in the SJV during the campaign.•CMAQ generally captured average diurnal cycle of ammonium nitrate in Fresno.
This study analyzes characteristics of an important alkyl amine species, dimethylamine (DMA), in cloud water over the northwest Atlantic. Data were gathered from the winter and summer 2020 ...deployments of the Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE) on board the HU-25 Falcon. Thirty-eight out of 98 samples exhibited DMA above detection limits, with the overwhelming majority in the winter season (33, 52% of winter samples) compared to summer (5, 14% of summer samples). Higher levels of DMA were observed in the winter, especially during cold air outbreaks (CAOs), which was also the case for NO
3
−
, NH
4
+
, and non sea salt-SO
4
2−
. This is in part due to a combination of low temperatures and offshore flow enhanced with continental pollutants such as from agriculture, industry, urban activity, and biomass burning. Unlike the inorganic acidic anions, oxalate was significantly correlated to DMA in summer and the winter in both CAO and non-CAO conditions, with a presumed reason being biomass burning supported by the consistent correlation between DMA and nss-K
+
in each season. ACTIVATE data are compared to a cloud water dataset from the northeast Pacific, with the latter exhibiting much higher DMA levels due possibly to more abundant ocean biological emissions. The seasonal differences and enhancement in DMA during CAO conditions relative to non-CAO winter days motivates continued research into the partitioning behavior of DMA and its sources as amines play an important role in carbon and nitrogen cycles in the marine environment.
This study analyzes characteristics of an important alkyl amine species, dimethylamine (DMA), in cloud water over the northwest Atlantic.
Process modeling of Aerosol‐cloud interaction (ACI) is essential to bridging gaps between observational analysis and climate modeling of aerosol effects in the Earth system and eventually reducing ...climate projection uncertainties. In this study, we examine ACI in summertime precipitating shallow cumuli observed during the Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE). Aerosols and precipitating shallow cumuli were extensively observed with in‐situ and remote‐sensing instruments during two research flight cases on 02 June and 07 June, respectively, during the ACTIVATE summer 2021 deployment phase. We perform observational analysis and large‐eddy simulation (LES) of aerosol effect on precipitating cumulus in these two cases. Given the measured aerosol size distributions and meteorological conditions, LES is able to reproduce the observed cloud properties by aircraft such as liquid water content (LWC), cloud droplet number concentration (Nc) and effective radius reff. However, it produces smaller liquid water path (LWP) and larger Nc compared to the satellite retrievals. Both 02 and 07 June cases are over warm waters of the Gulf Stream and have a cloud top height over 3 km, but the 07 June case is more polluted and has larger LWC. We find that the Na‐induced LWP adjustment is dominated by precipitation feedback for the 2 June precipitating case and there is no clear entrainment feedback in both cases. An increase of cloud fraction due to a decrease of aerosol number concentration is also shown in the simulations for the 02 June case.
Plain Language Summary
Aerosol‐cloud‐interaction (ACI) regulates the energy budget of the Earth and poses the largest uncertainty in climate projection. Particularly, ACI of low clouds is poorly understood and causes the spread of Earth System Models (ESMs) in predicting cloud and climate responses to aerosol changes. Process studies have shown a nonlinear cloud water amount and cloud fraction adjustments due to aerosol changes via precipitation and cloud top entrainment, which are not often captured correctly in ESMs. This study explores the physical mechanisms of ACI in marine low clouds with a focus on precipitating low clouds using a cloud process model and unprecedented field campaign measurements of meteorology states, cloud properties, and aerosols collected during the Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment. We show that the aerosol‐induced cloud water amount adjustment is dominated by changes in precipitation and there is no clear entrainment feedback in both cases. Our findings can help improve the representation of ACI within precipitating marine low clouds in ESMs.
Key Points
Aerosol‐cloud interactions in precipitating shallow cumuli are investigated using large‐eddy simulations (LES) and observations
LES show that aerosol‐induced cumulus cloud water adjustment is dominated by precipitation with no clear entrainment feedback
An increase in cloud fraction in response to aerosol number concentration decrease is shown in the precipitating cumuli
PDF
