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The 2017 revisions to the Regional Haze Rule clarify that visibility progress at Class I national parks and wilderness areas should be tracked on days with the highest anthropogenic contributions to haze (impairment). We compare the natural and anthropogenic contributions to haze in the western United States in 2011 estimated using the Environmental Protection Agency (EPA) recommended method and using model projections from the Comprehensive Air Quality Model with Extensions (CAMx) and the Particulate Source Apportionment Tool (PSAT). We do so because these two methods will be used by states to demonstrate visibility progress by 2028. If the two methods assume different natural and anthropogenic contributions, the projected benefits of reducing U.S. anthropogenic emissions will differ. The EPA method assumes that episodic elevated carbonaceous aerosols greater than an annual 95th percentile threshold are natural events. For western U.S. IMPROVE monitoring sites reviewed in this paper, CAMx-PSAT confirms these episodes are impacted by carbon from wildfire or prescribed fire events. The EPA method assumes that most of the ammonium sulfate is anthropogenic in origin. At most western sites CAMx-PSAT apportions more of the ammonium sulfate on the most impaired days to global boundary conditions and anthropogenic Canadian, Mexican, and offshore shipping emissions than to U.S. anthropogenic sources. For ammonium nitrate and coarse mass, CAMx-PSAT apportions greater contributions to U.S. anthropogenic sources than the EPA method assigns to total anthropogenic contributions. We conclude that for western IMPROVE sites, the EPA method is effective in selecting days that are likely to be impacted by anthropogenic emissions and that CAMx-PSAT is an effective approach to estimate U.S. source contributions. Improved inventories, particularly international and natural emissions, and further evaluation of global and regional model performance and PSAT attribution methods are recommended to increase confidence in modeled source characterization. Implications: The western states intend to use the CAMx model to project visibility progress by 2028. Modeled visibility response to changes in U.S. anthropogenic emissions may be less than estimated using the EPA assumptions based on total U.S. and international anthropogenic contributions to visibility impairment. Additional model improvements are needed to better account for contributions to haze from natural and international emissions in current and future modeling years. These improvements will allow more direct comparison of model and EPA estimates of natural and anthropogenic contributions to haze and future visibility progress.

We present the results of a VLA HI imaging survey aimed at understanding why some galaxies develop long extraplanar H$\alpha$ tails, becoming extreme jellyfish galaxies. The observations are centered on five extreme jellyfish galaxies, optically selected from the WINGS and OmegaWINGS surveys and confirmed to have long H$\alpha$ tails through MUSE observations. Each galaxy is located in a different cluster. In the observations there are in total 88 other spiral galaxies within the field of view (40'x40') and observed bandwidth (6500 km s$^{-1}$). We detect 13 of these 88 spirals, plus one uncatalogued spiral, with HI masses ranging from 1 to 7 $\times$ 10${^9}$ M$_{\odot}$. Many of these detections have extended HI disks, two show direct evidence for ram pressure stripping, while others are possibly affected by tidal forces and/or ram-pressure stripping. We stack the 75 non-detected spiral galaxies and find an average HI mass of 1.9 $\times$ 10$^{8}$ M$_{\odot}$, which given their average stellar mass, implies they are very HI deficient. Comparing the extreme jellyfish galaxies to the other disk galaxies, we find that they have a larger stellar mass than almost all disk galaxies and than all HI detected galaxies, they are at smaller projected distance from the cluster center and at higher relative velocity to the cluster mean than all HI detections and most non-detections. We conclude that the high stellar mass allows extreme jellyfish galaxies to fall deeply into the cluster before being stripped and the surrounding ICM pressure gives rise to their spectacular star-forming tails., Comment: 25 pages, 13 figures, accepted to ApJ

Satellite-based measurements of the column CH2O/NO2 ratio have previously been used to estimate near-surface ozone (O3) sensitivity (i.e., NOx or VOC limited), and the forthcoming launch of air quality-focused geostationary satellites provides a catalyst for reevaluating the ability of satellite-measured CH2O/NO2 to be used in this manner. In this study, we use a 0-D photochemical box model to evaluate O3 sensitivity and find that the relative rate of radical termination from radical-radical interactions to radical-NOx interactions (referred to as LROx/LNOx) provides a good indicator of maximum O3 production along NOx ridgelines. Using airborne measurements from NASA's Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relative to Air Quality (DISCOVER-AQ) deployments in Colorado, Maryland, and Houston, we show that in situ measurements of CH2O/NO2 can be used to indicate O3 sensitivity, but there is an important “transition/ambiguous” range whereby CH2O/NO2 fails to categorize O3 sensitivity, and the range and span of this transition/ambiguous range varies regionally. Then, we apply these findings to aircraft-derived column density measurements from DISCOVER-AQ and find that inhomogeneities in vertical mixing in the lower troposphere further degrades the ability of column CH2O/NO2 to indicate near-surface O3 sensitivity (i.e., the transition/ambiguous range is much larger than indicated by in situ data alone), and we hypothesize that the global transition/ambiguous range is sufficiently large to make the column CH2O/NO2 ratio unuseful for classifying near-surface O3 sensitivity. Lastly, we present a case study from DISCOVER-AQ-Houston that suggests that O3 sensitivity on exceedance days may be substantially different than on nonexceedance days (which may be observable from space) and explore the diurnal evolution of O3 sensitivity, O3 production, and the column CH2O/NO2 ratio. The results of these studies suggest that although satellite measurements of CH2O/NO2 alone may not be sufficient for accurately classifying near-surface O3 sensitivity, new techniques offered by geostationary platforms may nonetheless provide methods for using space-based measurements to develop O3 mitigation strategies.

The Salt Lake Valley experiences severe fine particulate matter pollution episodes in winter during persistent cold-air pools (PCAPs). We employ measurements throughout an entire winter from different elevations to examine the chemical and dynamical processes driving these episodes. Whereas primary pollutants such as NOx and CO were enhanced twofold during PCAPs, O3 concentrations were approximately threefold lower. Atmospheric composition varies strongly with altitude within a PCAP at night with lower NOx and higher oxidants (O3) and oxidized reactive nitrogen (N2O5) aloft. We present observations of N2O5 during PCAPs that provide evidence for its role in cold-pool nitrate formation. Our observations suggest that nighttime and early morning chemistry in the upper levels of a PCAP plays an important role in aerosol nitrate formation. Subsequent daytime mixing enhances surface PM2.5 by dispersing the aerosol throughout the PCAP. As pollutants accumulate and deplete oxidants, nitrate chemistry becomes less ...

US surface O3 responds to varying global-to-regional precursor emissions, climate, and extreme weather, with implications for designing effective air quality control policies. We examine these conjoined processes with observations and global chemistry-climate model (GFDL-AM3) hindcasts over 1980–2014. The model captures the salient features of observed trends in daily maximum 8 h average O3: (1) increases over East Asia (up to 2 ppb yr−1), (2) springtime increases at western US (WUS) rural sites (0.2–0.5 ppb yr−1) with a baseline sampling approach, and (3) summertime decreases, largest at the 95th percentile, and wintertime increases in the 50th to 5th percentiles over the eastern US (EUS). Asian NOx emissions have tripled since 1990, contributing as much as 65 % to modeled springtime background O3 increases (0.3–0.5 ppb yr−1) over the WUS, outpacing O3 decreases attained via 50 % US NOx emission controls. Methane increases over this period contribute only 15 % of the WUS background O3 increase. Springtime O3 observed in Denver has increased at a rate similar to remote rural sites. During summer, increasing Asian emissions approximately offset the benefits of US emission reductions, leading to weak or insignificant observed O3 trends at WUS rural sites. Mean springtime WUS O3 is projected to increase by ∼ 10 ppb from 2010 to 2030 under the RCP8.5 global change scenario. While historical wildfire emissions can enhance summertime monthly mean O3 at individual sites by 2–8 ppb, high temperatures and the associated buildup of O3 produced from regional anthropogenic emissions contribute most to elevating observed summertime O3 throughout the USA. GFDL-AM3 captures the observed interannual variability of summertime EUS O3. However, O3 deposition sink to vegetation must be reduced by 35 % for the model to accurately simulate observed high-O3 anomalies during the severe drought of 1988. Regional NOx reductions alleviated the O3 buildup during the recent heat waves of 2011 and 2012 relative to earlier heat waves (e.g., 1988, 1999). The O3 decreases driven by NOx controls were more pronounced in the southeastern US, where the seasonal onset of biogenic isoprene emissions and NOx-sensitive O3 production occurs earlier than in the northeast. Without emission controls, the 95th percentile summertime O3 in the EUS would have increased by 0.2–0.4 ppb yr−1 over 1988–2014 due to more frequent hot extremes and rising biogenic isoprene emissions.

Two specific fires from 2011 are tracked for local to regional scale contribution to ozone (O 3 ) and fine particulate matter (PM 2.5 ) using a freely available regulatory modeling system that includes the BlueSky wildland fire emissions tool, Spare Matrix Operator Kernel Emissions (SMOKE) model, Weather and Research Forecasting (WRF) meteorological model, and Community Multiscale Air Quality (CMAQ) photochemical grid model. The modeling system was applied to track the contribution from a wildfire (Wallow) and prescribed fire (Flint Hills) using both source sensitivity and source apportionment approaches. The model estimated fire contribution to primary and secondary pollutants are comparable using source sensitivity (brute-force zero out) and source apportionment (Integrated Source Apportionment Method) approaches. Model estimated O 3 enhancement relative to CO is similar to values reported in literature indicating the modeling system captures the range of O 3 inhibition possible near fires and O 3 production both near the fire and downwind. O 3 and peroxyacetyl nitrate (PAN) are formed in the fire plume and transported downwind along with highly reactive VOC species such as formaldehyde and acetaldehyde that are both emitted by the fire and rapidly produced in the fire plume by VOC oxidation reactions. PAN and aldehydes contribute to continued downwind O 3 production. The transport and thermal decomposition of PAN to nitrogen oxides (NO X ) enables O 3 production in areas limited by NO X availability and the photolysis of aldehydes to produce free radicals (HO X ) causes increased O 3 production in NO X rich areas. The modeling system tends to overestimate hourly surface O 3 at routine rural monitors in close proximity to the fires when the model predicts elevated fire impacts on O 3 and Hazard Mapping System (HMS) data indicates possible fire impact. A sensitivity simulation in which solar radiation and photolysis rates were more aggressively attenuated by aerosol in the plume reduced model O 3 but does not eliminate this bias. A comparison of model predicted daily average speciated PM 2.5 at surface rural routine network sites when the model predicts fire impacts from either of these fires shows a tendency toward overestimation of PM 2.5 organic aerosol in close proximity to these fires. The standard version of the CMAQ treats primarily emitted organic aerosol as non-volatile. An alternative approach for treating organic aerosol as semi-volatile resulted in lower PM 2.5 organic aerosol from these fires but does not eliminate the bias. Future work should focus on modeling specific fire events that are well characterized in terms of size, emissions, and have extensive measurements taken near the fire and downwind to better constrain model representation of important physical and chemical processes (e.g. aerosol photolysis attenuation and organic aerosol treatment) related to wild and prescribed fires.

The San Joaquin Valley (SJV) of California experiences high concentrations of particulate matter NH(4)NO(3) during episodes of meteorological stagnation in winter. A rich data set of observations related to NH(4)NO(3) formation was acquired during multiple periods of elevated NH(4)NO(3) during the Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) field campaign in SJV in January and February 2013. Here NH(4)NO(3) is simulated during the SJV DISCOVER-AQ study period with the Community Multiscale Air Quality (CMAQ) model, diagnostic model evaluation is performed using the DISCOVER-AQ data set, and integrated reaction rate analysis is used to quantify HNO(3) production rates. Simulated NO(3)(−) generally agrees well with routine monitoring of 24-hr average NO(3)(−), but comparisons with hourly average NO(3)(−) measurements in Fresno revealed differences at higher time resolution. Predictions of gas-particle partitioning of total nitrate (HNO(3) + NO(3)(−)) and NHx (NH(3) + NH(4)(+)) generally agree well with measurements in Fresno, although partitioning of total nitrate to HNO(3) is sometimes overestimated at low relative humidity in afternoon. Gas-particle partitioning results indicate that NH(4)NO(3) formation is limited by HNO(3) availability in both the model and ambient. NH(3) mixing ratios are underestimated, particularly in areas with large agricultural activity, and additional work on the spatial allocation of NH(3) emissions is warranted. During a period of elevated NH(4)NO(3), the model predicted that the OH + NO(2) pathway contributed 46% to total HNO(3)production in SJV and the N(2)O(5) heterogeneous hydrolysis pathway contributed 54%. The relative importance of the OH + NO(2) pathway for HNO(3) production is predicted to increase as NOx emissions decrease.

Determining effective strategies for mitigating surface ozone (O3) pollution requires knowledge of the relative ambient concentrations of its precursors, NOx, and VOCs. The space-based tropospheric column ratio of formaldehyde to NO2 (FNR) has been used as an indicator to identify NOx-limited versus NOx-saturated O3 formation regimes. Quantitative use of this indicator ratio is subject to three major uncertainties: (1) the split between NOx-limited and NOx-saturated conditions may shift in space and time, (2) the ratio of the vertically integrated column may not represent the near-surface environment, and (3) satellite products contain errors. We use the GEOS-Chem global chemical transport model to evaluate the quantitative utility of FNR observed from the Ozone Monitoring Instrument over three northern midlatitude source regions. We find that FNR in the model surface layer is a robust predictor of the simulated near-surface O3 production regime. Extending this surface-based predictor to a column-based FNR requires accounting for differences in the HCHO and NO2 vertical profiles. We compare four combinations of two OMI HCHO and NO2 retrievals with modeled FNR. The spatial and temporal correlations between the modeled and satellite-derived FNR vary with the choice of NO2 product, while the mean offset depends on the choice of HCHO product. Space-based FNR indicates that the spring transition to NOx-limited regimes has shifted at least a month earlier over major cities (e.g., New York, London, and Seoul) between 2005 and 2015. This increase in NOx sensitivity implies that NOx emission controls will improve O3 air quality more now than it would have a decade ago.

Two separate air quality model methodologies for estimating background ozone levels over the western U.S. are compared in this analysis. The first approach is a direct sensitivity modeling approach that considers the ozone levels that would remain after certain emissions are entirely removed (i.e., zero-out modeling). The second approach is based on an instrumented air quality model which tracks the formation of ozone within the simulation and assigns the source of that ozone to pre-identified categories (i.e., source apportionment modeling). This analysis focuses on a definition of background referred to as U.S. background (USB) which is designed to represent the influence of all sources other than U.S. anthropogenic emissions. Two separate modeling simulations were completed for an April–October 2007 period, both focused on isolating the influence of sources other than domestic manmade emissions. The zero-out modeling was conducted with the Community Multiscale Air Quality (CMAQ) model and the source apportionment modeling was completed with the Comprehensive Air Quality Model with Extensions (CAMx). Our analysis shows that the zero-out and source apportionment techniques provide relatively similar estimates of the magnitude of seasonal mean daily 8-h maximum U.S. background ozone at locations in the western U.S. when base case model ozone biases are considered. The largest differences between the two sets of USB estimates occur in urban areas where interactions with local NOx emissions can be important, especially when ozone levels are relatively low. Both methodologies conclude that seasonal mean daily 8-h maximum U.S. background ozone levels can be as high as 40–45 ppb over rural portions of the western U.S. Background fractions tend to decrease as modeled total ozone concentrations increase, with typical fractions of 75–100 percent on the lowest ozone days (

Ozone (O3) is a key air pollutant that is produced from precursor emissions and has adverse impacts on human health and ecosystems. In the U.S., the Clean Air Act (CAA) regulates O3 levels to protect public health and welfare, but unraveling the origins of surface O3 is complicated by the presence of contributions from multiple sources including background sources like stratospheric transport, wildfires, biogenic precursors, and international anthropogenic pollution, in addition to U.S. anthropogenic sources. In this report, we consider more than 100 published studies and assess current knowledge on the spatial and temporal distribution, trends, and sources of background O3 over the continental U.S., and evaluate how it influences attainment of the air quality standards. We conclude that spring and summer seasonal mean U.S. background O3 (USB O3), or O3 formed from natural sources plus anthropogenic sources in countries outside the U.S., is greatest at high elevation locations in the western U.S., with monthly mean maximum daily 8-hour average (MDA8) mole fractions approaching 50 parts per billion (ppb) and annual 4th highest MDA8s exceeding 60 ppb, at some locations. At lower elevation sites, e.g., along the West and East Coasts, seasonal mean MDA8 USB O3 is in the range of 20–40 ppb, with generally smaller contributions on the highest O3 days. The uncertainty in U.S. background O3 is around ±10 ppb for seasonal mean values and higher for individual days. Noncontrollable O3 sources, such as stratospheric intrusions or precursors from wildfires, can make significant contributions to O3 on some days, but it is challenging to quantify accurately these contributions. We recommend enhanced routine observations, focused field studies, process-oriented modeling studies, and greater emphasis on the complex photochemistry in smoke plumes as key steps to reduce the uncertainty associated with background O3 in the U.S.

The Weather Research and Forecasting (WRF) and Community Multiscale Air Quality (CMAQ) models were used to simulate a 10 day high-ozone episode observed during the 2013 Uinta Basin Winter Ozone Study (UBWOS). The baseline model had a large negative bias when compared to ozone (O3) and volatile organic compound (VOC) measurements across the basin. Contrary to other wintertime Uinta Basin studies, predicted nitrogen oxides (NO x ) were typically low compared to measurements. Increases to oil and gas VOC emissions resulted in O3 predictions closer to observations, and nighttime O3 improved when reducing the deposition velocity for all chemical species. Vertical structures of these pollutants were similar to observations on multiple days. However, the predicted surface layer VOC mixing ratios were generally found to be underestimated during the day and overestimated at night. While temperature profiles compared well to observations, WRF was found to have a warm temperature bias and too low nighttime mixing heights. Analyses of more realistic snow heat capacity in WRF to account for the warm bias and vertical mixing resulted in improved temperature profiles, although the improved temperature profiles seldom resulted in improved O3 profiles. While additional work is needed to investigate meteorological impacts, results suggest that the uncertainty in the oil and gas emissions contributes more to the underestimation of O3. Further, model adjustments based on a single site may not be suitable across all sites within the basin.

Determining effective strategies for mitigating surface ozone (O3) pollution requires knowledge of the relative ambient concentrations of its precursors, NOx, and VOCs. The space-based tropospheric column ratio of formaldehyde to NO2 (FNR) has been used as an indicator to identify NOx-limited versus NOx-saturated O3 formation regimes. Quantitative use of this indicator ratio is subject to three major uncertainties: (1) the split between NOx-limited and NOx-saturated conditions may shift in space and time, (2) the ratio of the vertically integrated column may not represent the near-surface environment, and (3) satellite products contain errors. We use the GEOS-Chem global chemical transport model to evaluate the quantitative utility of FNR observed from the Ozone Monitoring Instrument over three northern midlatitude source regions. We find that FNR in the model surface layer is a robust predictor of the simulated near-surface O3 production regime. Extending this surface-based predictor to a column-based FNR requires accounting for differences in the HCHO and NO2 vertical profiles. We compare four combinations of two OMI HCHO and NO2 retrievals with modeled FNR. The spatial and temporal correlations between the modeled and satellite-derived FNR vary with the choice of NO2 product, while the mean offset depends on the choice of HCHO product. Space-based FNR indicates that the spring transition to NOx-limited regimes has shifted at least a month earlier over major cities (e.g., New York, London, and Seoul) between 2005 and 2015. This increase in NOx sensitivity implies that NOx emission controls will improve O3 air quality more now than it would have a decade ago.

Natural emissions adopted in current regional air quality modeling are updated to better describe natural background ozone and PM concentrations for North America. The revised natural emissions include organosulfur from the ocean, NO from lightning, sea salt, biogenic secondary organic aerosol (SOA) precursors, and pre-industrial levels of background methane. The model algorithm for SOA formation was also revised. Natural background ozone concentrations increase by up to 4 ppb in annual average over the southeastern US and Gulf of Mexico due to added NO from lightning while the revised biogenic emissions produced less ozone in the central and western US. Natural PM2.5 concentrations generally increased with the revised natural emissions. Future year (2018) simulations were conducted for several anthropogenic emission reduction scenarios to assess the impact of the revised natural emissions on anthropogenic emission control strategies. Overall, the revised natural emissions did not significantly alter the ozone responses to the emissions reductions in 2018. With revised natural emissions, ozone concentrations were slightly less sensitive to reducing NOx in the southeastern US than with the current natural emissions due to higher NO from lightning. The revised natural emissions have little impact on modeled PM2.5 responses to anthropogenic emission reductions. However, there are substantial uncertainties in current representations of natural sources in air quality models and we recommend that further study is needed to refine these representations.

Operational, diagnostic, and comparative evaluations of two one-atmosphere regional models were performed for the full calendar year 2002 in support of regional haze regulatory applications in the eastern US. Using consistent emissions, meteorological and air quality data sets, the community multi-scale air quality and comprehensive air quality model with extensions models were exercised on a nested 36/12 km grid system and evaluated across a broad range of time and space scales for numerous gas-phase and fine particulate species derived from routine and research-grade ambient measurements at six monitoring networks. Performance by both models for speciated fine particulate matter (PM) across the eastern US ranged from quite good (e.g., SO42−) to poor (e.g., soil). For most species, model bias was higher in the winter and lower (usually negative) in the summer suggesting potential issues related to vertical mixing (e.g., too little in winter), temporal allocation of emissions, and/or other model science processes or inputs. These results may be used to (a) guide one-atmosphere model refinements, (b) improve data input preparation procedures, (c) evaluate methods for rigorous, stressful performance testing, and (d) clarify the uncertainty in model estimates for regional haze and PM2.5 control strategy programs.

Photochemical grid models are being used in technical analyses by the Visibility Improvement State and Tribal Association of the Southeast (VISTAS), a regional air quality planning organization in the southeastern United States, to support state implementation plans for regional haze and related air quality issues. VISTAS has embarked on a multi-phase process of testing and evaluating regional meteorological, emissions and air quality models that will be used to project visibility improvements as required by the regional haze rule. VISTAS has generated 2002 annual emissions and meteorological inputs for two photochemical grid models, the community multi-scale air quality (CMAQ) and the comprehensive air-quality model with extensions (CAMx), at a 36 km resolution for the continental US and at 12 km resolution for the eastern US. The two models were evaluated using speciated PM measurements from various monitoring networks and detailed analysis was performed for organic carbon (OC) mass using the IMPROVE, STN, and SEARCH networks. The differences in model performance between CMAQ and CAMx were used as a diagnostic tool to investigate performance issues for several compounds. CAMx performed substantially better than CMAQ for OC (defined as 1.4×measured organic carbon) which led to investigations into methods for improving the CMAQ OC model performance. The treatment of secondary organic aerosol (SOA) was identified as an area needing improvements in both models. The impact of replacing the CMAQ SOA parameters with those from CAMx was investigated. Further analysis identified several processes that are potentially important for SOA formation that are not treated in either model including, polymerization of the SOA into non-volatile particles and SOA formation from sesquiterpene, isoprene and other biogenic VOCs. A prototype mechanism for several of these missing processes was developed and the CMAQ SOA module was enhanced to include these SOA formation processes. SOA yields, specifically from biogenic emissions, were increased by the modified SOA module and CMAQ model performance for particulate OC at the IMPROVE, SEARCH, and STN sites in the VISTAS region was improved. © 2006 Elsevier Ltd. All rights reserved.

The Visibility Improvement State and Tribal Association of the Southeast (VISTAS) is one of five Regional Planning Organizations that is charged with the management of haze, visibility, and other regional air quality issues in the United States. The VISTAS Phase I work effort modeled three episodes (January 2002, July 1999, and July 2001) to identify the optimal model configuration(s) to be used for the 2002 annual modeling in Phase II. Using model configurations recommended in the Phase I analysis, 2002 annual meteorological (Mesoscale Meterological Model [MM5]), emissions (Sparse Matrix Operator Kernal Emissions [SMOKE]), and air quality (Community Multiscale Air Quality [CMAQ]) simulations were performed on a 36-km grid covering the continental United States and a 12-km grid covering the Eastern United States. Model estimates were then compared against observations. This paper presents the results of the preliminary CMAQ model performance evaluation for the initial 2002 annual base case simulation. Model performance is presented for the Eastern United States using speciated fine particle concentration and wet deposition measurements from several monitoring networks. Initial results indicate fairly good performance for sulfate with fractional bias values generally within +/-20%. Nitrate is overestimated in the winter by approximately +50% and underestimated in the summer by more than -100%. Organic carbon exhibits a large summer underestimation bias of approximately -100% with much improved performance seen in the winter with a bias near zero. Performance for elemental carbon is reasonable with fractional bias values within +/- 40%. Other fine particulate (soil) and coarse particular matter exhibit large (80-150%) overestimation in the winter but improved performance in the summer. The preliminary 2002 CMAQ runs identified several areas of enhancements to improve model performance, including revised temporal allocation factors for ammonia emissions to improve nitrate performance and addressing missing processes in the secondary organic aerosol module to improve OC performance.

This note presents a straightforward method to correct sea-salt-emission particle-size distributions according to local relative humidity. The proposed method covers a wide range of relative humidity (0.45–0.99) and its derivation incorporates recent laboratory results on sea-salt properties. The formulas are given as functions of relative humidity and compared with growth factors derived from earlier theoretical work. Application of this method to several common open-ocean and surf-zone sea-salt-particle source functions is described. The resulting sea-salt-emission aerosol distributions can be used directly in atmospheric model simulations without further correction.

The weekend effect on ozone, a phenomenon with high ozone concentration at weekend, was analyzed using the data measured at 7 photochemical assessment monitoring stations (PAMS), (1) volatile organic compounds (VOCs) monitoring station and (2) routine ambient air quality monitoring stations in southern California during ozone season from 1995 to 2001. Weekend/weekday differences of ozone, ozone precursors and PM10 concentrations and the light scatter, composition and reactivity of VOCs in morning traffic rush time and afternoon peak ozone time were compared. The possible causes for the weekend effect were discussed. The significant weekend effect was observed in southern California except in areas close to beach and far downwind direction from L.A. Downtown. On average, the peak O3 and max 8 h average O3 concentrations at weekend were 20% and 22%, respectively, higher than those on weekday while the concentrations of O3 precursors and PM10 and the light scatter were lower at weekday in southern California. In morning traffic rush time, the average concentrations of NOx, CO, NMOC and PM10 and the light scatter at weekend were about 37%, 18%, 15%, 14% and 9%, respectively, lower than those on weekday. In afternoon peak ozone time, the average concentrations of NOx, CO, NMOC and PM10 and the light scatter at weekend were about 29%, 13%, 24%, 17% and 17%, respectively, lower than those on weekday. The reactivities of VOCs in morning traffic rush time and afternoon peak ozone time at weekend were 17% and 26%, respectively, lower than those on weekday. VOCs sensitivity for ozone formation and a decrease NOx emissions at weekend can well explain the weekend effect in southern California. Less scatter of sunlight due to lower fine particle concentration at weekend results in enhanced ozone formation might be another possible cause for the weekend effect.

Three probes for diagnosing photochemical dynamics are presented and applied to specialized ambient surface-level observations and to a numerical photochemical model to better understand rates of production and other process information in the atmosphere and in the model. However, care must be taken to ensure that rate and process information is not confounded by inappropriate averaging over these diurnally changing photochemical dynamics. One probe, the [O3] response surface probe [O3]/[NOX], is used here as a chemical filter to select NOX-limited hours in the observations and the simulations. Other probes used here are the fraction NOZ/NOY, a measure of chemical aging, and a measure of the production efficiency of O3 per NOX converted, [O3] to [NOZ]. The key ambient measurements for all three probes are accurate [NO2] and a reliable estimate of total NOY. Good agreement is shown between models and observations in cases where local photochemical production dominates and where model emissions inputs are thought to be mostly complete. We interpret this agreement to mean that the photochemical processing in CMAQ is substantially similar to that in the atmosphere. More importantly, we see that the three probes provide consistent information about photochemical processing, especially when used together.

For the purposes of developing optimal emissions control strategies, efficient approaches are needed to identify the major sources or groups of sources that contribute to elevated ozone (O3) concentrations. Source based apportionment techniques implemented in photochemical grid models track sources through the physical and chemical processes important to the formation and transport of air pollutants. Photochemical model source apportionment has been used to estimate impacts of specific sources, groups of sources (sectors), sources in specific geographic areas, and stratospheric and lateral boundary inflow on O3. The implementation and application of a source apportionment technique for O3 and its precursors, nitrogen oxides (NOx) and volatile organic compounds (VOC), for the Community Multiscale Air Quality (CMAQ) model are described here. The Integrated Source Apportionment Method (ISAM) O3 approach is a hybrid of source apportionment and source sensitivity in that O3 production is attributed to precursor sources based on O3 formation regime (e.g., for a NOx-sensitive regime, O3 is apportioned to participating NOx emissions). This implementation is illustrated by tracking multiple emissions source sectors and lateral boundary inflow. NOx, VOC, and O3 attribution to tracked sectors in the application are consistent with spatial and temporal patterns of precursor emissions. The O3 ISAM implementation is further evaluated through comparisons of apportioned ambient concentrations and deposition amounts with those derived from brute force zero-out scenarios, with correlation coefficients ranging between 0.58 and 0.99 depending on specific combination of target species and tracked precursor emissions. Low correlation coefficients occur for chemical regimes that have strong non-linearity in O3 sensitivity, which demonstrates different functionalities between source apportionment and zero-out approaches, depending on whether sources of interest are either to be accounted for pollutant levels in a given scenario, or to be perturbed to invoke alternate scenarios.

Background: Variability and logistic complexity of mechanical ventilatory support of acute respiratory distress syndrome, and need to standardize care among all clinicians and patients, led University of Utah/LDS Hospital physicians, nurses, and engineers to develop a comprehensive computerized protocol. This bedside decision support system was the basis of a multicenter clinical trial (1993-1998) that showed ability to export a computerized protocol to other sites and improved efficacy with computer- versus physician-directed ventilatory support. The Memorial Hermann Hospital Shock Trauma intensive care unit (ICU) (Houston, TX; a Level I trauma center and teaching affiliate of The University of Texas Houston Medical School) served as one of the 10 trial sites and recruited two thirds of the trauma patients. Results from the trauma patient subgroup at this site are reported to answer three questions: Can a computerized protocol be successfully exported to a trauma ICU? Was ventilator management different between study groups? Was patient outcome affected? Methods: Sixty-seven trauma patients were randomized at the Memorial Hermann Shock Trauma ICU site. Protocol assigned patients had ventilatory support directed by the bedside respiratory therapist using the computerized protocol. Nonprotocol patients were managed by physician orders. Results: Of the 67 trauma patients randomized, 33 were protocol (age 40 ± 3; Injury Severity Score [ISS] 26 ± 3; 73% blunt) and 34 were nonprotocol (age 38 ± 2; ISS 25 ± 2; 76% blunt). For the protocol group, the computerized protocol was used 96% of the time of ventilatory support and 95% of computer-generated instructions were followed by the bedside respiratory therapist. Outcome measures (i.e., survival, ICU length of stay, morbidity, and barotrauma) were not significantly different between groups. FIO 2 ≥ 0.6 and Pplateau ≥ 35 cm H 2 O exposures were less for the protocol group. Conclusion: A computerized protocol for bedside decision support was successfully exported to a trauma center, and effectively standardized mechanical ventilatory support of trauma-induced acute respiratory distress syndrome without adverse effect on patient outcome.

We used an analysis of radical propagation efficiency and OH chain length in a simple trajectory model to propose combinations of long-lived species that distinguish conditions in which O3 concentration ([O3]) is NOx-limited and radical-limited. We further examined these indicators in a three-dimensional grid model. We proposed several new indicators including [H2O2]/([O3]+[NO2]), [O3]/[NOx], and a measure using the OH rate constant weighted concentrations of NO2 and hydrocarbons. Our analysis also supports the use of several indicators previously proposed by other researchers, including [O3]/[HNO3] and [H2O2]/[HNO3]. We found that [HCHO]/[NO2] was more useful than the previously proposed [HCHO]/[NOy]. We found that the indicators easily distinguished extremely NOx-limited or extremely radical-limited regimes but did not reliably distinguish conditions closer to the transition between these two regimes. We propose that a combined analysis using photochemical model simulations and a large set of indicators of both [O3] sensitivity and local odd oxygen production (P(Ox)) sensitivity to VOC and NOx provides the most complete and useful description of [O3] sensitivity. Time series of the indicators, at least from mid-morning to late afternoon, provide useful information about the evolution of [O3] sensitivity during the day. Values of the indicators change depending on the [O3] level due in part to the effects of miscellaneous OH and HO2 termination reactions and to the effects of the composition of the HC mixture on P(Ox). Further evaluation of these indicators using modeling studies, measurements, and test cases with NOx or VOC emissions changes are needed to determine how reliably they distinguish NOx-and radical-limited conditions.

We used a simple trajectory model and a three-dimensional grid model to evaluate several indicators that can be used to predict the sensitivity of odd oxygen production (P(Ox)) to changes in emissions of anthropogenic nonmethane hydrocarbons (VOC) and nitrogen oxides (NOx = NO + NO2). To perform the evaluation, we augmented the model to include new diagnostic outputs such as rates of P(Ox), rates of conversion of NOx to unreactive nitrogen, and radical chain length. We used the new diagnostic outputs to explain the model-predicted sensitivity of P(Ox) to changes in VOC and NOx emissions. We found that the ozone ridgeline, which distinguishes between NOx-limited and radical-limited conditions, is determined by a ridgeline of maximum OH chain length. We examined the radical propagation reactions which affect OH chain length, and we developed four indicators related to radical propagation efficiency: I(HC,NO2) which approximates the fraction of OH that reacts with hydrocarbons; I(NO,RO2) which approximates the fraction of HO2 that reacts with NO; the ratio of [O3]/[NOx] which affects the balance between radical initiation and propagation; and [HO2] which is the dominant term in P(H2O2)/P(HNO3). Each of these indicators distinguishes conditions in which instantaneous P(Ox) is primarily sensitive to either NOx emissions reductions or VOC emissions reductions.

We evaluated the effect of a 20% reduction in the rate constant of the reaction of the hydroxyl radical with nitrogen dioxide to produce nitric acid (OH+NO 2 →HNO 3 ) on model predictions of ozone mixing ratios ([O 3 ]) and the effectiveness of reductions in emissions of volatile organic compounds (VOC) and nitrogen oxides (NO x ) for reducing [O 3 ]. By comparing a model simulation with the new rate constant to a base case scenario, we found that the [O 3 ] increase was between 2 and 6% for typical rural conditions and between 6 and 16% for typical urban conditions. The increases in [O 3 ] were less than proportional to the reduction in the OH+NO 2 rate constant because of negative feedbacks in the photochemical mechanism. Next, we used two different approaches to evaluate how the new OH+NO 2 rate constant changed the effectiveness of reductions in emissions of VOC and NO x : first, we evaluated the effect on [O 3 ] sensitivity to small changes in emissions of VOC (d[O 3 ]/d E VOC ) and NO x (d[O 3 ]/d E NO x ); and secondly, we used the empirical kinetic modeling approach to evaluate the effect on the level of emissions reduction necessary to reduce [O 3 ] to a specified level. Both methods showed that reducing the OH+NO 2 rate constant caused control strategies for VOC to become less effective relative to NO x control strategies. We found, however, that d[O 3 ]/d E VOC and d[O 3 ]/d E NO x did not quantitatively predict the magnitude of the change in the control strategy because the [O 3 ] response was nonlinear with respect to the size of the emissions reduction. We conclude that model sensitivity analyses calculated using small emissions changes do not accurately characterize the effect of uncertainty in model inputs (in this case, the OH+NO 2 rate constant) on O 3 attainment strategies. Instead, the effects of changes in model inputs should be studied using large changes in precursor emissions to approximate realistic attainment scenarios.

The Regional Acid Deposition Model (RADM) was used in a sensitivity study at 80 km and 20 km grid resolutions to simulate urban and regional tropospheric conditions in the eastern U.S. for the time period 19 July to 12 August 1988. Using one-at-a-time (OAT) sensitivity perturbations and a mini-global analysis we varied three model inputs in the range of their known uncertainties: mixing height; emissions of nitrogen oxides (NO x ) and volatile organic compounds (VOC); and the rate constant for the reaction OH + NO 2 → HNO 3 . Two measures, ozone concentration ([O 3 ]) and the ratio [O 3 ]/[NO x ], were used to assess the photochemical system's sensitivity response on an 03 response surface. We find that: (1) these input uncertainties change the system's state in different ways, altering either the [O 3 ] or the system's response to emissions reductions, or changing both responses together; (2) the [O 3 ] /[NO x ] measure successfully predicts the direction and relative degree of change in the system state while [O 3 ] does not; and (3) for most of the days and locations we have examined, the system's responses to uncertainties simulated OAT are nearly additive when compared with the mini-global case, and that both of the sensitivity measures we assessed correctly tracked this additivity. We conclude that incorporating the [O 3 ]/[NO x ] ratio is a significant first step in constructing a useful sensitivity vector for understanding systems-level changes in the model. However, additional measures that can successfully track the change of shape of the response surface are still needed.

Continuous venous air emboli have been detected in the inferior vena cava and smaller veins using transesophageal echocardiography in patients with positive pressure ventilation and associated pulmonary barotrauma. The authors hypothesized that gas entered the venous circulation, following dissection of small vessels at several sites in the subcutaneous or retro-peritoneal soft tissues.The present study was designed to determine if a comparable venous gas embolism occurred in anesthetized dogs, after creation of a pneumomediastinum.Using transesophageal echocardiography, we observed 11 anesthetized dogs mechanically ventilated with positive end-expiratory pressure, while mediastinal air was introduced through a catheter at a rate of 0.5 ml/kg/min.A continuous stream of bubbles appeared in the inferior vena cava in 8/11 dogs (73%) after an infusion period of 280 +/- 81 min. A surge of bubbles was commonly observed following abdominal massage and was often associated with a transient decrease of end-tidal carbon dioxide tensions. In two dogs the air infusion rate was reduced to 0.25 mg/kg/min, and bubbles were detected in the inferior vena cava for as long as 16 consecutive hours.We conclude that in anesthetized dogs mechanically ventilated with positive end-expiratory pressure, unremitting pneumomediastinum is usually followed by continuous venous air embolism. A mechanism hypothesized for venous gas entry in the clinical condition of positive end-expiratory pressure ventilation with subcutaneous gas is suggested by this model.

A case is presented of acute intraoperative atelectasis causing profound hypoxaemia in a patient undergoing a combined epidural-general anaesthetic for hip surgery in the lateral position. The pathophysiology of the resultant ventilation-perfusion mis-match and the effects of applied positive end-expiratory pressure in the lateral position are explored. The emergency management is assessed, with emphasis on the role of bronchoscopy in diagnosis and treatment of this rare cause of life-threatening hypoxaemia in the operating room. This patient with risk factors for respiratory complications may have benefited from preoperative bronchoscopy to assist in lung expansion.

We compared four immunoassays for serum and urine myoglobin. Within-run CVs were 5-13%, with biases seen between assays. Myoglobin was stable for 1 month in serum and 12 days in urine when the pH was adjusted to between 8.0 and 9.5. Hemoglobin caused no interference. We assayed 91 pairs of serum and timed urine specimens from 41 patients admitted for acute trauma or rhabdomyolysis. Most were treated with mannitol and alkalinization. Upon initial presentations, 21 patients with either low serum myoglobin concentrations (< 400 micrograms/L) or high myoglobin clearances (> or = 4 mL/min) had normal creatinine clearances and no clinical evidence of renal disease. The remaining 20 had low myoglobin clearances. Seven were in rhabdomyolysis-induced acute renal failure, or subsequently developed this complication. We suggest that low myoglobin clearance may indicate a high risk for developing renal failure or may be an early marker for kidney dysfunction. Low myoglobin clearance may prove useful in indicating failure of prophylactic treatment to clear myoglobin.

An experimental clinical chemistry analyzer system was designed and built to demonstrate the feasibility of clinical chemistry as part of a medical-care system at NASA's planned space station Freedom. We report the performance of the experimental analyzer, called a medical development unit (MDU), for selected analytes in a laboratory setting in preparation for a preliminary clinical trial at patients' bedsides in an intensive-care unit. Within-run CVs ranged from 0.7% for sodium to 7.1% for phosphorus; day-to-day CVs ranged from 1.0% for chloride to 23.4% for calcium. Correlation of patients' blood sample analyses compared well with those by Ektachem E700 and other high-volume central laboratory analyzers (r ranged from 0.933 for creatine kinase MB isoenzyme to 0.997 for potassium), except for hemoglobin (r = 0.901) and calcium (r = 0.823). Although several CVs obtained in this study exceeded theoretical desired precision limits based on biological variations, performance was adequate for clinical laboratory diagnosis. We examined the effect of potentially interfering concentrations of hemoglobin, bilirubin, and lipids: the only effect was negative interference with calcium analyses by high concentrations of bilirubin. We also examined the effects of preanalytical variables and the performance of experimental sample-transfer cups designed to retain sample and reference liquid in microgravity. Continued development of the MDU system is recommended, especially automation of sample processing.

Seventeen patients with chemotherapy-resistant metastatic sarcoma were treated with whole body hyperthermia (WBH) combined simultaneously with 1-3-Bis(2-chloroethyl)-1-nitrosourea (BCNU). All of the patients had chemotherapy resistant metastases to major organ sites. Patients were heated to 41.8-42.0 degrees C for 2 h using an insulated blanket heating technique. Two patients (12%) experienced partial responses (PR). In addition, four objective tumour responses (OR) lasting more than 4 months were documented. One patient with previously rapidly growing chondrosarcoma pulmonary metastases experienced stable disease (SD) for 38 months from the onset of treatment. Median survival of seven patients with responding tumours (PR, OR and SD) compared with 10 patients with progressive disease was 15 versus 2 months, respectively. Cumulative thrombocytopenia was a therapy-limiting toxicity of the combined treatment, and occurred in six of seven patients. Acute toxicities attributable to WBH alone included transient thrombocytopenia in all patients, non-cardiogenic pulmonary oedema in two patients, and mild hypotension in five patients. Acute granulocytosis was observed in all patients. No treatment related deaths occurred. These data suggest that WBH combined with chemotherapy is associated with disease response in patients with chemotherapy-resistant, widely disseminated sarcoma metastases.

A 3-month study was performed in a teaching hos pital to determine the impact of intensive, focused utilization management on the average length of stay and average total charges in a carefully defined group of indigent patients. Prompt admission review was performed, the treatment plan ascertained, and a physician advisor notified. The attending physician was informed by a physician advisor of the patient's financial class, and assistance with expediting patient care and discharge planning was offered. Daily con current review monitored the treatment and dis charge plans. The study compared 73 patients with a control group of 191 patients of similar financial class and diagnosis related groups (DRGs) for the immedi ately preceding 3 months. Compared with the control patients, the study patients experienced a 23% de crease in average length of stay and 16% decrease in average total charges. This study indicates that an intensive utilization management effort in a teaching hospital can be effective without compromising the quality of care.

Hypophosphatemia is associated with a number of undesirable physiologic consequences and has been reported to occur frequently in trauma patients. We studied patients in the immediate posttraumatic period to document a) the decrease in serum P, b) renal P excretion, and c) the response to prophylactic PO4 administration. In both group 1 (n = 12) and group 2 (n = 10) patients, we measured serum P, creatinine, ionized Ca, urinary P excretion, and creatinine clearance daily for the first 3 to 4 days postinjury. Patients in group 2 also received 0.5 mmol/kg.day of PO4 for the first 48 h after admission. Group 1 patients exhibited a significant (p less than .05) decrease in serum P over the first 24 h (1.00 +/- 0.30 to 0.75 +/- 0.23 mmol/L). In contrast, group 2 patients did not demonstrate a decrease in serum P. Urinary P excretion in group 1 accounts for the observed decrease in serum P. The results of our study show that the immediate posttraumatic period is associated with a decrease in serum P and massive urinary P excretion. We also showed that prophylactic administration of 0.5 mmol PO4/kg.day prevents serum P decrease.

As recommended by Kuhn et al. (1998) a comprehensive mechanism evaluation or intercomparison requires that the mechanisms be evaluated for a large number of VOC and NOx scenarios, and, ideally, for the full response surface. Key difficulties in performing such an evaluation include: the large number of VOC/NOx scenarios to be performed; the large number of species concentrations and reaction rates to be analyzed; and the temporal variability in the evolution of species concentrations. We have demonstrated here modifications to the widely used OZIPR model that facilitate mechanism evaluations. New model outputs are created allowing the PAVE visualization package to be used to perform sophisticated, time-dependent analyses for multiple data sets. In addition, outputs that describes the budgets of HOx, NOy and Ox allows for convenient evaluation of the important component chemical processes. Our example analysis here shows that there are important differences in the CB4.99 and the SAPRC99 mechanisms, particularly in the Ox production efficiency per NOx for NOx-limited conditions and in the HOx budget for radical-limited conditions. It is not possible to conclude which mechanism is more correct, but the model tool demonstrated here will allow mechanism developers to more readily assess the effects of future revisions to these photochemical mechanisms, and to determine which chemical process require better elucidation in future chamber and kinetics experiments.

Anthropogenic emissions into the atmosphere of gaseous pollutants such as nitrogen oxides (NO x ) and volatile organic compounds (VOC) produce secondary atmospheric pollutants, including ozone (O 3 ), nitric acid (HNO 3 ), and aerosol nitrates (NO 3 ) that may have adverse effects on wildland ecosystems. It is difficult to quantify the sources and magnitude of the deposition fluxes of these species using ambient monitoring studies because field measurements are expensive and typically have poor spatial coverage. Moreover, ambient monitoring is not well suited for determining the sources and transport of pollutants nor for identifying optimal control strategies to reduce pollutant exposure. Complex chemistry-transport models have been widely used for short-term modeling of urban and regional air quality and have been used for long-term modeling of acid deposition in the eastern US. We report results of annual model simulations in the western US designed specifically to study regional haze and including predictions of deposition of O 3 and nitrogen (N) species in the Sierra Nevada. The modeling system used is the US Environmental Protection Agency's (USEPA) Community Multiscale Air Quality (CMAQ) model, which was developed in the “third generation” (Models-3) modeling system that supersedes earlier generation models such as the Regional Acid Deposition Model. The development of emissions inventories, meteorological fields, and the ambient data necessary for model performance evaluation is a large-scale, complex effort that involves multiple institutions and years of effort. We describe the model formulation and the necessary data sets, and we provide some sample results of deposition of O 3 and N in the Sierra Nevada. There are large uncertainties in the deposition fluxes estimated in this modeling study, and considerable further work is required to develop more accurate input data. Moreover, the current study used a relatively poor spatial resolution with a grid cell dimension of 36 km. Finer resolution modeling will be required to simulate more confidently the wind fields and the spatial variability of deposition fluxes in the Sierra Nevada.

Publisher Summary This chapter describes the detail of tropospheric photochemistry, higher-order models (HOMs), and forecasts the effects of current and future changes depends on having the right micro-scale theoretical constituents and having them correctly incorporated in the model. The approach to probing the shores of our ignorance is based on three supporting and interlocking principles: (1) the guiding insight of a high-level conceptual description, such as the causal descriptions of the ocean conveyor-belt; (2) instrumentation of the model to reveal its finely detailed internal mechanisms and process structure; and (3) development of new probes, which measures or indices that can be routinely constructed from combinations of readily observed environmental state variables, whose purpose will be to reveal, more incisively, the real system's potential to experience structural change. The approach presented in this chapter points rather towards novel ways of observing the real world, almost setting an agenda for innovation in instrumentation technology.

The authors were intimately involved in choosing and implementing a clinical information system for an integrated medical care delivery system. We will describe our experiences in implementing the first stages of an electronic medical record. We will consider the problems encountered, solutions that were found and continuing areas of sub-optimal performance.

The role of biogenic hydrocarbons on ozone modeling has been a controversial issue since the 1970s. In recent years, changes in biogenic emission algorithms have resulted in large increases in estimated isoprene emissions. This paper describes a recent algorithm, the second generation of the Biogenic Emissions Inventory System (BEIS2). A sensitivity analysis is performed with the Regional Acid Deposition Model (RADM) to examine how increased isoprene emissions generated with BEIS2 can influence the modeling of elevated ozone concentrations and the response of ozone to changes to volatile organic compound (VOC) and nitrogen oxide (NOx) emissions across much of eastern North America. Increased isoprene emissions are found to produce a predicted shift in elevated ozone concentrations from VOC sensitivity to NOx sensitivity over many areas of eastern North America. Isoprene concentrations measured near Scotia, Pennsylvania, during the summer of 1988 are compared with RADM estimates of isoprene and provide support for the veracity of the higher isoprene emissions in BEIS2, which are about a factor of 5 higher than BEIS1 during warm, sunny conditions. Copyright 1998 by the American Geophysical Union.

Objectives To directly measure airway pressures proximal and distal to endotracheal tubes during conventional synchronized intermittent mandatory ventilation (SIMV) and pressure controlled-inverse ratio ventilation (PC-IRV), and to compare them with these values measured by the ventilator. Design Prospective, nonrandomized study. Setting Surgical intensive care unit at a trauma center. Patients Group 1: Eight intubated adult patients connected to mechanical ventilators in the SIMV mode were studied. All patients required mechanical ventilation following traumatic injuries. Group 2: Five intubated adult patients with adult respiratory distress syndrome connected to mechanical ventilators were studied. Interventions A small polyethylene catheter was threaded through each endotracheal tube such that it could be positioned to measure pressures proximal and distal to the tubes. Measurements and main results During SIMV, a significant pressure gradient exists across endotracheal tubes. In addition, although initiation of PC-IRV did lead to a lower peak airway pressure measured proximally, intratracheal peak airway pressure was unchanged. Conclusions A pressure gradient exists during inspiration from the ventilator to the trachea in mechanically ventilated patients. Tracheal pressures cannot be predicted from proximal airway pressure monitors because of marked variation in endotracheal tube resistance in vivo. Initiation of PC-IRV does not result in a decrease in peak airway pressure when measured intratracheally.

Head-injured patients require maintenance of systemic hemodynamics as well as attention to cerebral hemodynamics. Most head-injured patients have increased metabolic oxygen consumption, mild hypertension, and increased cardiac indices. Assessment of regional perfusion, difficult in many patients, includes monitoring of urinary output. In head-injured patients, especially those with multiple injuries, the two most important goals are preservation of cerebral perfusion pressure (mean arterial pressure minus intracranial pressure) and maintenance of systemic oxygen availability (cardiac index times arterial oxygen content).