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.
We have developed semi-independent methods for determining CH2O scavenging efficiencies (SEs) during strong midlatitude convection over the western, south-central Great Plains, and southeastern ...regions of the United States during the 2012 Deep Convective Clouds and Chemistry (DC3) Study. The Weather Research and Forecasting model coupled with chemistry (WRF-Chem) was employed to simulate one DC3 case to provide an independent approach of estimating SEs and the opportunity to study CH2O retention in ice when liquid drops freeze. Measurements of CH2O in storm inflow and outflow were acquired on board the NASA DC-8 and the NSF/National Center for Atmospheric Research Gulfstream V (GV) aircraft employing cross-calibrated infrared absorption spectrometers. This study also relied heavily on the nonreactive tracers i-/n-butane and i-/n-pentane measured on both aircraft in determining lateral entrainment rates during convection as well as their ratios to ensure that inflow and outflow air masses did not have different origins. Of the five storm cases studied, the various tracer measurements showed that the inflow and outflow from four storms were coherently related. The combined average of the various approaches from these storms yield remarkably consistent CH2O scavenging efficiency percentages of: 54%±3% for 29 May; 54%±6% for 6 June; 58%±13% for 11 June; and 41±4% for 22 June. The WRF-Chem SE result of 53% for 29 May was achieved only when assuming complete CH2O degassing from ice. Further analysis indicated that proper selection of corresponding inflow and outflow time segments is more important than the particular mixing model employed. Key Points Obtained remarkably consistent CH2O scavenging efficiencies of 41 to 58% in all but one storm Six of seven different methods produced the same result on one storm within a 7% range Erroneous scavenging efficiencies result when inflow and outflow are not coherently related
Healthy Steps (HS) represents a significant innovation in the way pediatric primary care can be delivered. Based on the standards and principles of Bright Futures and the American Academy of ...Pediatrics Health Supervision Guidelines, HS enhances and expands traditional pediatric care by including a child development specialist (Healthy Steps specialist) as part of the pediatric practice team. Services offered by this person, typically a nurse, early childhood educator, or social worker, include more time to spend discussing preventive issues during well-child visits, home visits, a telephone information line exclusively addressing developmental and behavioral concerns, new written materials, and more seamless linkages to community resources and parent support groups. The original HS cohort consisted of 15 pediatric practices in a variety of settings (private practices, health centers, pediatric training programs). Evaluated for the effects of HS on their family were 3737 intervention and comparison families. HS families received significantly more preventive and developmental services, compared to families in the control group. HS families were also less likely to be dissatisfied with their pediatric primary care. Additionally, HS had a positive impact on parenting in many areas including adherence to health visits, nutritional practices, developmental stimulation, appropriate disciplinary techniques, and correct sleeping position. Other outcome measures (such as initiation or duration of breastfeeding, child development knowledge, sense of competence, and reports of child language development at 2 years of age) did not differ between intervention and comparison group. Compared to other early childhood intervention efforts, HS offers a comparable positive impact on parenting at a relatively inexpensive cost: an estimated 400 dollars per family per year (compared to 4500 dollars from Early Head Start). Approximately 3 years after the evaluation of HS ended, 10 of the original 24 sites are still in operation, and an additional 24 sites have started up. Although funding and reimbursement remain an important barrier, continued growth of HS suggests an abiding interest in this approach to expand and enhance preventive and developmental care in pediatric primary care.
Sulfur chemistry has been incorporated in the National Center for Atmospheric Research Community Climate Model in an internally consistent manner with other parameterizations in the model. The model ...predicts mixing ratios of dimethylsulfide (DMS), SO2, SO42−, H2O2. Processes that control the mixing ratio of these species include the emissions of DMS and SO2, transport of each species, gas‐ and aqueous‐phase chemistry, wet deposition, and dry deposition of species. Modeled concentrations agree quite well with observations for DMS and H2O2, fairly well for SO2, and not as well for SO42−. The modeled SO42− tends to underestimate observed SO42− at the surface and overestimate observations in the upper troposphere. The SO2 and SO42− species were tagged according to the chemical production pathway and whether the sulfur was of anthropogenic or biogenic origin. Although aqueous‐phase reactions in cloud accounted for 81% of the sulfate production rate, only ∼50–60% of the sulfate burden in the troposphere was derived from cloud chemistry. Because cloud chemistry is an important source of sulfate in the troposphere, the importance of H2O2 concentrations and pH values was investigated. When prescribing H2O2 concentrations to clear‐sky values instead of predicting H2O2, the global‐averaged, annual‐averaged in‐cloud production of sulfate increased. Setting the pH of the drops to 4.5 also increased the in‐cloud production of sulfate. In both sensitivity simulations, the increased in‐cloud production of sulfate decreased the burden of sulfate because less SO2 was available for gas‐phase conversion, which contributes more efficiently to the tropospheric sulfate burden than does aqueous‐phase conversion.
Transport is a key parameter in air quality research and plays a dominant role in the Colorado Northern Front Range Metropolitan Area (NFRMA), where terrain‐induced flows and recirculation patterns ...can lead to vigorous mixing of different emission sources. To assess different transport processes and their connection to air quality in the NFRMA during the FRAPPÉ and DISCOVER‐AQ campaigns in summer 2014, we use the Weather Research and Forecasting Model with inert tracers. Overall, the model represents well the measured winds, and the inert tracers are in good agreement with observations of comparable trace gas concentrations. The model tracers support the analysis of surface wind and ozone measurements and allow for the analysis of transport patterns and interactions of emissions. A main focus of this study is on characterizing pollution transport from the NFRMA to the mountains by mountain‐valley flows and the potential for recirculating pollution back into the NFRMA. One such event on 12 August 2014 was well captured by the aircraft and is studied in more detail. The model represents the flow conditions and demonstrates that during upslope events, frequently, there is a separation of air masses that are heavily influenced by oil and gas emissions to the north and dominated by urban emissions to the south. This case study provides evidence that NFRMA pollution not only can impact the nearby foothills and mountain areas to the east of the Continental Divide but that pollution can “spillover” into the valleys to the west of the Continental Divide.
Key Points
Upslope flows are a frequent occurrence on high ozone days in the NFRMA, thereby impacting remote mountain sites
Aircraft measurements and model tracers confirm transport of pollution to the mountains and spillover into the valleys to the west of the Continental Divide
The northern foothills are frequently impacted by oil and gas sources, while the southern foothills more frequently experience impact from urban sources
We examine the balance between processes that contribute to the global and regional distributions of sulfate aerosol in the Earth's atmosphere using a set of simulations from the National Center for ...Atmospheric Research Community Climate Model, Version 3. The analysis suggests that the seasonal cycle of SO2 and SO42− are controlled by a complex interplay between transport, chemistry and deposition processes. The seasonal cycle of these species is not strongly controlled by temporal variations in emissions but by seasonal variations in volume of air processed by clouds, mass of liquid water serving as a site for aqueous chemistry, amount of oxidant available for the conversion from SO2 to SO42−, vertical transport processes, and deposition. A tagging of the sulfate by emission region (Europe, North America, Asia, and rest of world ROW), chemical pathway (gaseous versus in‐cloud), and type of emissions (anthropogenic versus biogenic) is used to differentiate the balance of processes controlling the production and loading from this material. Significant differences exist in the destiny of SO2 molecules emitted from the several regions. An SO2 molecule emitted from the ROW source region has a much greater potential to form sulfate than one emitted from, for example, Europe. A greater fraction of the SO2 molecules is oxidized that originate from ROW compared with other areas, and once formed, the sulfate has a longer residence time (that is, it is not readily scavenged). The yield of sulfate from ROW sources of SO2 is a factor of 4 higher than that of Europe. A substantially higher fraction of the SO2 emitted over Europe is oxidized to sulfate through the ozone pathway compared to other regions. The analysis suggests that there are significant differences in the vertical distribution, and horizontal extent, of the propagation of sulfate emitted from the several source regions. Sulfate from Asian source regions reaches the farthest from its point of origin and makes a significant contribution to burdens in both hemispheres, primarily from plumes reaching out in the upper troposphere. Sulfate from other source regions tends to remain trapped in their hemisphere of origin.
By using a three‐dimensional convective cloud model to simulate the July 10, 1996, Stratospheric‐Tropospheric Experiment: Radiation, Aerosols, and Ozone‐Deep Convection experiment storm, we ...investigate the fate of tracers of varying solubilities in midlatitude convection. The tracer distribution resulting from the interactions of the soluble tracers with the cloud hydrometeors is illustrated for two cases. The first case assumes that the dissolved tracer in the cloud water or rain completely degasses when the parent hydrometeor is converted to ice, snow, or hail through microphysical processes. The second case assumes that the dissolved tracer is retained in the ice, snow, or hail. We find that when soluble tracers are degassed, both low‐ and high‐solubility tracers are transported to the upper troposphere. When tracers are retained in ice hydrometeors, the highly soluble tracers are not ultimately transported to the upper troposphere but, instead, are precipitated out of the upper troposphere by snow and hail. Tracers of low solubility are transported upward, similar to passive tracer transport. The key microphysical processes that control these results are the accretion of cloud water by snow and hail. For the simulation in which retention of tracers in ice was considered, highly soluble scalars (105 M atm−1) have a scavenging efficiency >55% and have a mass change in the upper troposphere (8–15 km mean sea level) of −0.5×105 kg to 0 for a 3‐hour period, while a passive scalar has a mass change of 2.3×105 kg.
We report results of a cloud chemistry numerical modeling intercomparison, which shows good agreement among gas‐aqueous photochemistry box models that are being used in the community. For the case ...studied, cloud chemistry depleted concentrations of CH2O, CH3OOH, HNO3, and O3, while H2O2 (in the absence of sulfur chemistry), NO, and NO2 increased. Because parcels of air usually flow in and out of cloud in a matter of minutes rather than remain in cloud for an hour, an optional simulation was performed in which frequent brief cloud encounters were represented. Representing a cloud intermittently rather than continuously does not alter the total concentration of many of the species. However CH2O and HCOOH concentrations are decreased and increased, respectively, because of the timing of the CH2O production during clear‐sky intervals and its destruction during cloudy intervals. Further differences between a continuous cloud simulation and an intermittent cloud simulation are expected if pH is allowed to vary during the cloud periods. Simulating an intermittent cloud brought out the importance of using a chemistry time step that is a multiple of the cloud time step because deviations of results from a simulation in which the chemistry time step did not coincide with the appearance and disappearance of cloud were quite large. To better quantify the effect of cloud on HOx photochemistry, future investigations should include nonmethane hydrocarbon and sulfur chemistry. Future cloud chemistry modeling intercomparisons should bring in cloud physical and chemical measurements so that the models can be evaluated with observations.
Virtually no literature exists on the labor market for social workers. Fragmentary evidence suggests that this market is highly segmented by education; that many people who do not have social work ...degrees work in social work jobs, at least at the lower levels; that people who want to be social workers have such a strong commitment to the career of social work that relative wages make relatively little difference to their career decisions; and that employers often hire applicants without degrees for social work jobs. These factors tend to depress wages for social workers. Suggestions are made for a research and data collection program to make possible a definitive analysis of the social work labor market.
To learn what possible influence a megacity and an industrial region, both of which have poor air quality, have on the global scale, sulfate aerosol derived from Mexico City and from southeast China ...is examined. It is found that the highest values of sulfate from Mexico City mostly travel westward and northward. Sulfate from southeast China travels eastward, and its distribution encircles the Earth in summer and autumn. Mexico City, which emits ∼1% of the global anthropogenic sulfur emissions, contributes ∼1% to the global sulfate burden. Southeast China, which emits 11.6% of the global anthropogenic sulfur emissions, contributes 9% to the global sulfate burden, a nonlinear response between emissions and burden. When the anthropogenic sulfur emissions are doubled in the two regions, the sulfate burden derived from Mexico City approximately doubles, but the sulfate burden from southeast China more than doubles. An examination of the sulfate budget indicates that for sulfate derived from southeast China more sulfate is produced via gas‐phase reaction, thus allowing the sulfate to be less susceptible to wet deposition. We qualitatively analyze black carbon aerosol from Mexico City and southeast China and determine that hydrophilic black carbon has a lifetime similar to sulfate aerosol when the emitted black carbon is assumed to be of hydrophilic form. When the emitted black carbon is hydrophobic and its transfer rate to the hydrophilic form is 1.9 days, which is the same as the global sulfur dioxide lifetime, the lifetime of hydrophilic black carbon is 3.5 days longer than sulfate. The difference between the two types of aerosol is attributed to the aqueous production pathway of sulfate and consequently its availability to rain out. If the transfer rate is 5 days, then hydrophilic black carbon is found in regions with little cloud activity thus increasing its lifetime to 10 days or more.
PDF
