The Acidity of Atmospheric Particles and Clouds Pye, Havala O T; Nenes, Athanasios; Alexander, Becky ...
Atmospheric chemistry and physics,
04/2020, Letnik:
20, Številka:
8
Journal Article
Recenzirano
Odprti dostop
Acidity, defined as pH, is a central component of aqueous chemistry. In the atmosphere, the acidity of condensed phases (aerosol particles, cloud water, and fog droplets) governs the phase ...partitioning of semi-volatile gases such as HNO
, NH
, HCl, and organic acids and bases as well as chemical reaction rates. It has implications for the atmospheric lifetime of pollutants, deposition, and human health. Despite its fundamental role in atmospheric processes, only recently has this field seen a growth in the number of studies on particle acidity. Even with this growth, many fine particle pH estimates must be based on thermodynamic model calculations since no operational techniques exist for direct measurements. Current information indicates acidic fine particles are ubiquitous, but observationally-constrained pH estimates are limited in spatial and temporal coverage. Clouds and fogs are also generally acidic, but to a lesser degree than particles, and have a range of pH that is quite sensitive to anthropogenic emissions of sulfur and nitrogen oxides, as well as ambient ammonia. Historical measurements indicate that cloud and fog droplet pH has changed in recent decades in response to controls on anthropogenic emissions, while the limited trend data for aerosol particles indicates acidity may be relatively constant due to the semi-volatile nature of the key acids and bases and buffering in particles. This paper reviews and synthesizes the current state of knowledge on the acidity of atmospheric condensed phases, specifically particles and cloud droplets. It includes recommendations for estimating acidity and pH, standard nomenclature, a synthesis of current pH estimates based on observations, and new model calculations on the local and global scale.
Ozone is a greenhouse gas and air pollutant that is harmful to human health and plants. During the summer in the southeastern US, many regional and global models are biased high for surface ozone ...compared to observations. Past studies have suggested different solutions including the need for updates to model representation of clouds, chemistry, ozone deposition, and emissions of nitrogen oxides (NOx) or biogenic hydrocarbons. Here, due to the high biogenic emissions in the southeastern US, more comprehensive and updated isoprene and terpene chemistry is added into CESM/CAM-chem (Community Earth System Model/Community Atmosphere Model with full chemistry) to evaluate the impact of chemistry on simulated ozone. Comparisons of the model results with data collected during the Studies of Emissions Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) field campaign and from the US EPA (Environmental Protection Agency) CASTNET (Clean Air Status and Trends Network) monitoring stations confirm the updated chemistry improves simulated surface ozone, ozone precursors, and NOx reservoir compounds. The isoprene and terpene chemistry updates reduce the bias in the daily maximum 8 h average (MDA8) surface ozone by up to 7 ppb. In the past, terpene oxidation in particular has been ignored or heavily reduced in chemical schemes used in many regional and global models, and this study demonstrates that comprehensive isoprene and terpene chemistry is needed to reduce surface ozone model biases. Sensitivity tests were performed in order to evaluate the impact of lingering uncertainties in isoprene and terpene oxidation on ozone. Results suggest that even though isoprene emissions are higher than terpene emissions in the southeastern US, remaining uncertainties in isoprene and terpene oxidation have similar impacts on ozone due to lower uncertainties in isoprene oxidation. Additionally, this study identifies the need for further constraints on the aerosol uptake of organic nitrates derived from isoprene and terpenes in order to reduce uncertainty in simulated ozone. Although the updates to isoprene and terpene chemistry greatly reduce the ozone bias in CAM-chem, a large bias remains. Evaluation against SEAC4RS field campaign results suggests future improvements to horizontal resolution and cloud parameterizations in CAM-chem may be particularly important for further reducing this bias.
Using an interactive aerosol‐climate model we find that absorbing anthropogenic aerosols, whether coexisting with scattering aerosols or not, can significantly affect the Indian summer monsoon ...system. We also show that the influence is reflected in a perturbation to the moist static energy in the sub‐cloud layer, initiated as a heating by absorbing aerosols to the planetary boundary layer. The perturbation appears mostly over land, extending from just north of the Arabian Sea to northern India along the southern slope of the Tibetan Plateau. As a result, during the summer monsoon season, modeled convective precipitation experiences a clear northward shift, coincidently in general agreement with observed monsoon precipitation changes in recent decades particularly during the onset season. We demonstrate that the sub‐cloud layer moist static energy is a useful quantity for determining the impact of aerosols on the northward extent and to a certain degree the strength of monsoon convection.
Because explicit prediction of the electrical activity in storms is computationally expensive and the processes are still poorly understood, an attractive way to predict lightning flash rates in ...numerical models is to rely on correlations between the flash rate and available model parameters. Predicted flash rates can be used for applications such as the parameterization to infer lightning‐produced nitrogen oxides. In this study, the potential for six model parameters (precipitation ice mass, ice water path, ice mass flux product, updraft volume, maximum vertical velocity, and cloud top height) to predict lightning rate has been investigated in a cloud‐resolving model framework. The Weather Research and Forecasting model (WRF) is used to simulate two different storms: the 10 July 1996 severe storm that occurred over the High Plains and the 13 July 2005 airmass thunderstorm near Huntsville, Alabama. It is shown that the WRF model reproduces the structure of the two storms. Results show that the maximum updraft velocity gives a good flash rate proxy for the severe storm. The ice mass flux product and precipitation ice mass can reproduce the flash rate trend but not the magnitude. The flash rate estimated from the cloud top height does not match the observed flash rate trend and value of the severe storm, but is in good agreement for the airmass thunderstorm. The ice water path predicts flash rate fairly well for the severe storm, but overpredicts it for the airmass thunderstorm. The updraft volume predicts flash rate poorly for both storms.
Numerical simulations of a thunderstorm event that occurred in the pre‐monsoon season over the North‐Eastern region of India (NEI) and Bangladesh are performed using Weather Research and Forecasting ...(WRF) Advanced Research Weather Research and Forecasting Model (ARW, version 3.8.1). Doppler weather radar indicates severe convective activity lasted for more than 10 hr. These extremely deep convective clouds with minimum cloud‐top temperature −70 °C at 19 km were triggered by the mixing of a moist air mass transported from the Bay of Bengal in the south and dry air transported from the northwest. A cyclonic circulation observed over the Tibetan plateau is likely to be associated with the strong southerly low‐level wind over NEI, as the plateau acts as a source of heat‐lows during the pre‐monsoon season. The coexistence of ice particles and supercooled water in the storms resulted in a large number of lightning flashes during the storm as observed from the Tropical Rainfall Measuring Mission Lightning Imaging Sensor (TRMM‐LIS). Co‐location of supercooled cloud water droplets helps in forming graupel through riming that plays a vital role in these convective systems. Lightning flashes calculated from WRF simulation using the Morrison microphysical and cloud top height based dynamical lightning parametrization scheme was found comparable with the observed flashes from TRMM‐LIS. Since the WRF model could simulate the thunderstorm, we recommend using this state‐of‐the‐art regional model in thunderstorm and lightning predictions for northeast India which would be useful in preparedness for such extreme events.
Nested domains selected for the present study with d01, d02, d03 and d04 having horizontal resolution 27, 9, 3 and 1 km grid spacing respectively. The dot indicated the DWR radar location (Agartala), the star indicates the location of sounding observation station Dhaka and the square shows the location of aircraft observations near Silchar, Assam during the CAIPEEX field experiment in 2009.
The Deep Convective Clouds and Chemistry (DC3) field experiment produced an exceptional dataset on thunderstorms, including their dynamical, physical, and electrical structures and their impact on ...the chemical composition of the troposphere. The field experiment gathered detailed information on the chemical composition of the inflow and outflow regions of midlatitude thunderstorms in northeast Colorado, west Texas to central Oklahoma, and northern Alabama. A unique aspect of the DC3 strategy was to locate and sample the convective outflow a day after active convection in order to measure the chemical transformations within the upper-tropospheric convective plume. These data are being analyzed to investigate transport and dynamics of the storms, scavenging of soluble trace gases and aerosols, production of nitrogen oxides by lightning, relationships between lightning flash rates and storm parameters, chemistry in the upper troposphere that is affected by the convection, and related source characterization of the three sampling regions. DC3 also documented biomass-burning plumes and the interactions of these plumes with deep convection.
To study aerosol‐cloud interactions over the Gangetic Basin of India, the Weather Research and Forecasting model coupled with chemistry (WRF‐Chem) has been applied to a typical monsoon depression ...event prevalent between the 23 and 29 August 2009. This event was sampled during the Cloud Aerosol Interaction and Precipitation Enhancement EXperiment (CAIPEEX) aircraft campaign, providing measurements of aerosol and cloud microphysical properties from two sorties. Comparison of the simulated meteorological, thermodynamical, and aerosol fields against satellite and in situ aircraft measurements illustrated that the westward propagation of the monsoon depression and the cloud, aerosol, and rainfall spatial distribution was simulated reasonably well using anthropogenic emission rates from Monitoring Atmospheric Composition and Climate project along with cityZEN projects (MACCity)+Intercontinental Chemical Transport Experiment Phase B anthropogenic emission rates. However,the magnitude of aerosol optical depth was underestimated by up to 50%. A simulation with aerosol emissions increased by a factor of 6 over the CAIPEEX campaign domain increased the simulated aerosol concentrations to values close to the observations, mainly within boundary layer. Comparison of the low‐aerosol simulation and high‐aerosol simulation for the two sorties illustrated that more anthropogenic aerosols increased the cloud condensing nuclei (CCN) and cloud droplet mass concentrations. The number of simulated cloud droplets increased while the cloud droplet effective radii decreased, highlighting the importance of CCN‐cloud feedbacks over this region. The increase in simulated anthropogenic aerosols (including absorbing aerosols) also increased the temperature of air parcels below clouds and thus the convective available potential energy (CAPE). The increase in CAPE intensified the updraft and invigorated the cloud, inducing formation of deeper clouds with more ice‐phase hydrometeors for both cases. These case studies provide evidence of aerosol‐induced cloud invigoration over the Gangetic Basin.
Key Points
Aircraft sampled microphysical and aerosol fields are used to evaluate WRF‐Chem
Westward propagation of the monsoon depression reduced AOD over central India
Aerosol‐induced perturbations invigorated convection via low‐level heating and cloud physics
This study employs a large-eddy simulation (LES) technique to predict the air exchange rate (ACH) and pollutant exchange rate (PCH) for street canyons of aspect ratio (
h
/
b
, ...building-height-to-street-width) 0.5, 1.0, and 2.0 at a Reynolds number
(
Re
)
of 12,000 and a Schmidt number
(
Sc
)
of 0.72. The air ventilation and pollutant dilution of the street canyons are investigated by means of the distribution, average concentration, and retention time of pollutant in the street canyons. The flow in the street canyons at this
Re
and
Sc
lies in the wake-interference flow regime, in which the recirculations are isolated from the free-stream flow and the pollutant removal is governed by turbulent transport. Based on the LES database, the ACH and PCH of the street canyons are determined by the roof-level transient turbulence properties. The ACH increases with decreasing
h
/
b
, which is in line with the common observation of the better air ventilation in street canyons of smaller
h
/
b
. The PCH is found to be equal to the amount of pollutant emitted. Positive PCH shows that the pollutant removal rate is greater than the ground-level pollutant emission rate. As a consequence, some of the pollutant in the free surface layer, which originated from the street canyon, re-enters the canyon, lengthening the pollutant retention time in the street canyon. If pollutants from upstream sources reside in the free stream flow, the pollutant entrainment would contribute to degrading the air quality in the street canyons.
Background
Women of lower socioeconomic status (SES) with early‐stage breast cancer are more likely to report poorer physician‐patient communication, lower satisfaction with surgery, lower ...involvement in decision making, and higher decision regret compared to women of higher SES. The objective of this study was to understand how to support women across socioeconomic strata in making breast cancer surgery choices.
Methods
We conducted a 3‐arm (Option Grid, Picture Option Grid, and usual care), multisite, randomized controlled superiority trial with surgeon‐level randomization. The Option Grid (text only) and Picture Option Grid (pictures plus text) conversation aids were evidence‐based summaries of available breast cancer surgery options on paper. Decision quality (primary outcome), treatment choice, treatment intention, shared decision making (SDM), anxiety, quality of life, decision regret, and coordination of care were measured from T0 (pre‐consultation) to T5 (1‐year after surgery.
Results
Sixteen surgeons saw 571 of 622 consented patients. Patients in the Picture Option Grid arm (n = 248) had higher knowledge (immediately after the visit T2 and 1 week after surgery or within 2 weeks of the first postoperative visit T3), an improved decision process (T2 and T3), lower decision regret (T3), and more SDM (observed and self‐reported) compared to usual care (n = 257). Patients in the Option Grid arm (n = 66) had higher decision process scores (T2 and T3), better coordination of care (12 weeks after surgery or within 2 weeks of the second postoperative visit T4), and more observed SDM (during the surgical visit T1) compared to usual care arm. Subgroup analyses suggested that the Picture Option Grid had more impact among women of lower SES and health literacy. Neither intervention affected concordance, treatment choice, or anxiety.
Conclusions
Paper‐based conversation aids improved key outcomes over usual care. The Picture Option Grid had more impact among disadvantaged patients.
Lay Summary
The objective of this study was to understand how to help women with lower incomes or less formal education to make breast cancer surgery choices.
Compared with usual care, a conversation aid with pictures and text led to higher knowledge. It improved the decision process and shared decision making (SDM) and lowered decision regret. A text‐only conversation aid led to an improved decision process, more coordinated care, and higher SDM compared to usual care. The conversation aid with pictures was more helpful for women with lower income or less formal education.
Conversation aids with pictures and text helped women make better breast cancer surgery choices.
A paper‐based pictorial conversation aid (pictures plus text) is beneficial to all patients with early‐stage breast cancer and particularly to disadvantaged patients. Between‐surgeon variation suggests that the maximal impact of such interventions requires standardized physician training combined with these interventions.
A significant source of ozone in the troposphere is transport from the stratosphere. The stratospheric contribution has been estimated mainly using global models that attribute the transport process ...largely to the global‐scale Brewer‐Dobson circulation and synoptic‐scale dynamics associated with upper tropospheric jet streams. We report observations from research aircraft that reveal additional transport of ozone‐rich stratospheric air downward into the upper troposphere by a leading‐line‐trailing‐stratiform mesoscale convective system with convection overshooting the tropopause altitude. The fine‐scale transport demonstrated by these observations poses a significant challenge to global models that currently do not resolve storm‐scale dynamics. Thus, the upper tropospheric ozone budget simulated by global chemistry‐climate models where large‐scale dynamics and photochemical production from lightning‐produced NO are the controlling factors may require modification.
Key Points
Tropopause‐reaching MCSs entrain ozone‐rich stratospheric air into troposphereAirborne lidar measurement is key to revealing this transport mechanismA missing transport pathway for ozone budget in major global models
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