Concentrations Of Particulate Pollutants Research Articles

Concentration of Gas and Particulate Air Pollutants in Suwałki Analysed in Relation to Meteorological Conditions

The aim of the work was to assess the changeability of concentrations of nitrogen dioxide, sulphur dioxide and suspended dust PM10 in an urban area of Suwalki depending on selected meteorological elements. The work takes into account daily data concerning the ambient concentration of gas and particulate pollutants and meteorological data from the station of air quality monitoring and the Institute of Meteorology and Water Management (IMGW) in Suwalki in 1994-2003. In Suwalki, time distribution of SO2 and PM10 in contrast with NO2 showed a distinct seasonal structure. In a heating season the ambient concentrations of SO2 and PM10 were considerably higher than in the summer. The deterioration of air quality in Suwalki resulted from an upward tendency of NO2 ,S O 2 and PM10 concentrations in 1994-2003, with exception of the period from May to July when the dust showed a considerable downward tendency. The biggest number of significant relations between gas and particulate pollutants and meteorological elements were shown in a heating season, especially in January and December, the least in the summer, in July and September. In climate conditions of north-east Poland the following elements were unfavourable to air cleanliness: wind velocity below 2.2 and 1.9 m s -1 for NO2, for a heating and summer season

Panel discussion review: session 1 — exposure assessment and related errors in air pollution epidemiologic studies

Examining the validity of exposure metrics used in air pollution epidemiologic models has been a key focus of recent exposure assessment studies. The objective of this work has been, largely, to determine what a given exposure metric represents and to quantify and reduce any potential errors resulting from using these metrics in lieu of true exposure measurements. The current manuscript summarizes the presentations of the co-authors from a recent EPA workshop, held in December 2006, dealing with the role and contributions of exposure assessment in addressing these issues. Results are presented from US and Canadian exposure and pollutant measurement studies as well as theoretical simulations to investigate what both particulate and gaseous pollutant concentrations represent and the potential errors resulting from their use in air pollution epidemiologic studies. Quantifying the association between ambient pollutant concentrations and corresponding personal exposures has led to the concept of defining attenuation factors, or alpha. Specifically, characterizing pollutant-specific estimates for alpha was shown to be useful in developing regression calibration methods involving PM epidemiologic risk estimates. For some gaseous pollutants such as NO2 and SO2, the associations between ambient concentrations and personal exposures were shown to be complex and still poorly understood. Results from recent panel studies suggest that ambient NO2 measurements may, in some locations, be serving as surrogates to traffic pollutants, including traffic-related PM2.5, hopanes, steranes, and oxidized nitrogen compounds (rather than NO2).

Apportionment of Ambient Primary and Secondary Fine Particulate Matter during a 2001 Summer Intensive Study at the CMU Supersite and NETL Pittsburgh Site

Gaseous and particulate pollutant concentrations associated with five samples per day collected during a July 2001 summer intensive study at the Pittsburgh Carnegie Mellon University (CMU) Supersite were used to apportion fine particulate matter (PM2.5) into primary and secondary contributions using PMF2. Input to the PMF2 analysis included the concentrations of PM2.5 nonvolatile and semivolatile organic material, elemental carbon (EC), ammonium sulfate, trace element components, gas-phase organic material, and NO(x), NO2, and O3 concentrations. A total of 10 factors were identified. These factors are associated with emissions from various sources and facilities including crustal material, gasoline combustion, diesel combustion, and three nearby sources high in trace metals. In addition, four secondary sources were identified, three of which were associated with secondary products of local emissions and were dominated by organic material and one of which was dominated by secondary ammonium sulfate transported to the CMU site from the west and southwest. The three largest contributors to PM2.5 were secondary transported material (dominated by ammonium sulfate) from the west and southwest (49%), secondary material formed during midday photochemical processes (24%), and gasoline combustion emissions (11%). The other seven sources accounted for the remaining 16% of the PM2.5. Results obtained at the CMU site were comparable to results previously reported at the National Energy Technology Laboratory (NETL), located approximately 18 km south of downtown Pittsburgh. The major contributor at both sites was material transported from the west and southwest. Some difference in nearby sources could be attributed to meteorology as evaluated by HYSPLIT model back-trajectory calculations. These findings are consistent with the majority of the secondary ammonium sulfate in the Pittsburgh area being the result of contributions from distant transport, and thus decoupled from local activity involving organic pollutants in the metropolitan area. In contrast, the major local secondary sources were dominated by organic material.

Spatio-temporal characteristics of gaseous and particulate pollutants in an urban region of Kolkata, India

This study deals with air quality monitoring in an urban region of Kolkata, consisting of residential, commercial and industrial sites having high population density and pollution. Concentrations of ambient SO 2 (sulfur dioxide), NO 2, (nitrogen dioxide), NH 3 (ammonia) and PM 10 (particulate matter passing through a size selective impactor inlet with a 50% efficiency cut-off at 10 μm aerodynamic diameter) were measured once in a week for 24 h at selected residential and industrial sites and 8 h at a commercial site. The meteorological parameters (wind speed, wind direction, rainfall, temperature and relative humidity) were collected simultaneously from the Indian Meteorological Department, Kolkata. The daily average concentrations of SO 2, NO 2, NH 3 and PM 10 were observed to be 12.3 ± 9.2, 32.5 ± 14.2, 36.3 ± 19.7 and 140.1 ± 43.1 μg/m 3 at the residential site, with 21.3 ± 15.7, 49.9 ± 9.8, 34.7 ± 13.5 and 196.6 ± 88.2 μg/m 3 at the industrial site, respectively. The corresponding (8 h average) values at the commercial site were 15.5 ± 11.9, 39.9 ± 17.3, 33.9 ± 13.3 and 276.1 ± 71.4 μg/m 3. Winter concentrations of ambient SO 2, NO 2, NH 3 and PM 10 were observed to be higher irrespective of the monitoring sites and duration of sampling, suggesting longer residence times of these pollutants in the atmosphere during winter due to stagnant conditions and low mixing heights. The SO 2/NO 2 ratios at the residential, commercial and industrial sites were found to be 0.38, 0.42 and 0.43, respectively. These low SO 2/NO 2 ratios are indicative of major emissions from mobile sources within the city. Spearman's rank correlation analysis showed an inverse relationship between the measured gaseous and particulate pollutant concentrations with the observed wind speed, rainfall, temperature and relative humidity. The data were analyzed using varimax-rotated principal component analysis for the residential and industrial sites. In principal component analysis three factors were drawn out of the seven variables, which represent 84% of the variance. The results show that local emissions dominate the concentration of SO 2, NO 2, NH 3, and PM 10. The major sources of emissions affecting this urban area include mobile sources along with contributions from industrial sources, coal-fired power plants and domestic heating.

Water-Soluble Ions and Trace Metals in Airborne Particles Over Urban Areas of the State of São Paulo, Brazil: Influences of Local Sources and Long Range Transport

The atmosphere over Brazilian cities is influenced by a variety of emissions sources. In this study, aerosol collection and back-trajectory analysis were used to determine the influence of local and remote sources. Aerosols were collected at three locations within the state of Sao Paulo: one megacity and two cities in which sugar cane burning in the surroundings is observed. We quantified the major water-soluble inorganic ions and trace metals. As expected, vehicle emissions influenced the atmosphere of the megacity heavily, and sugar cane burning influenced that of the other locations. During the period of this experiment the back-trajectory analysis revealed that air masses are transported into the state from the northeast of Brazil, where biomass burning occurs. Multivariate statistical analysis revealed that the two principal components account for 48.5% of the total data variance. We conclude that local sources have a strong impact on the concentrations of particulate matter and pollutants. Remote sources also contribute to the concentrations of aerosol pollutants.

Effects of exposure to air pollution on blood coagulation.

Consistent evidence has indicated that air pollution increases the risk of cardiovascular diseases. The underlying mechanisms linking air pollutants to increased cardiovascular risk are unclear. We investigated the association between the pollution levels and changes in such global coagulation tests as the prothrombin time (PT) and the activated partial thromboplastin time (APTT) in 1218 normal subjects from the Lombardia Region, Italy. Plasma fibrinogen and naturally occurring anticoagulant proteins were also evaluated. Hourly concentrations of particulate (PM10) and gaseous pollutants (CO, NO2, SO2, and O3) were obtained from 53 monitoring sites covering the study area. Generalized additive models were applied to compute standardized regression coefficients controlled for age, gender, body mass index, smoking, alcohol, hormone use, temperature, day of the year, and long-term trends. The PT became shorter with higher ambient air concentrations at the time of the study of PM10 (coefficient = -0.06; P < 0.05), CO (coefficient = -0.11; P < 0.001) and NO2 (coefficient =-0.06; P < 0.05). In the 30 days before blood sampling, the PT was also negatively associated with the average PM(10) (coefficient = -0.08; P < 0.05) and NO2 (coefficient = -0.08; P < 0.05). No association was found between the APTT and air pollutant levels. In addition, no consistent relations with air pollution were found for fibrinogen, antithrombin, protein C and protein S. This investigation shows that air pollution is associated with changes in the global coagulation function, suggesting a tendency towards hypercoagulability after short-term exposure to air pollution. Whether these changes contribute to trigger cardiovascular events remains to be established.

Modeling of air quality with a modified two-dimensional Eulerian model: A case study in the Pearl River Delta (PRD) region of China

A modified two-dimensional Eulerian air quality model was used to simulate both the gaseous and particulate pollutant concentrations during October 21-24, 2004 in the Pearl River Delta (PRD) region, China. The most significant improvement to the model is the added capability to predict the secondary organic aerosols (SOA) concentrations because of the inclusion of the SOA formation chemistry. The meteorological input data were prepared using the CALMET meteorological model. The concentrations of aerosol-bound species such as NO3−, NH4+, SO42-, and SOA were calculated in the fine particle size range (<2.5 μm). The results of the two-dimensional model were compared to the measurements at the ground level during the PRD Intensive Monitoring Campaign. Overall, there were good agreements between the measured and modeled concentrations of inorganic aerosol components and O3. Both the measured and the modeled results indicated that the maximum hourly O3 concentrations exceeded the China National Air Quality Standard. The predicted 24-h average SOA concentrations were in reasonable agreement with those predicted by the method of minimum OC/EC ratio.

Seasonal Variations of PM10 and TSP in Residential and Industrial Sites in an Urban Area of Kolkata, India

The objective of the study is to investigate seasonal and spatial variations of PM10 (particulate matter with aerodynamic diameter less than or equal to 10 microm) and TSP (total suspended particulate matter) of an Indian Metropolis with high pollution and population density from November 2003 to November 2004. Ambient concentration measurements of PM10 and TSP were carried out at two monitoring sites of an urban region of Kolkata. Monitoring sites have been selected based on the dominant activities of the area. Meteorological parameters such as wind speed, wind direction, rainfall, temperature and relative humidity were also collected simultaneously during the sampling period from Indian Meteorological Department, Kolkata. The 24 h average concentrations of PM10 and TSP were found in the range 68.2-280.6 microg/m3 and 139.3-580.3 microg/m3 for residential (Kasba) area, while 62.4-401.2 microg/m3 and 125.7-732.1 microg/m3 for industrial (Cossipore) area, respectively. Winter concentrations of particulate pollutants were higher than other seasons, irrespective of the monitoring sites. It indicates a longer residence time of particulates in the atmosphere during winter due to low winds and low mixing height. Spread of air pollution sources and non-uniform mixing conditions in an urban area often result in spatial variation of pollutant concentrations. The higher particulate pollution at industrial area may be attributed due to resuspension of road dust, soil dust, automobile traffic and nearby industrial emissions. Particle size analysis result shows that PM10 is about 52% of TSP at residential area and 54% at industrial area.

Air pollution and the heart

Despite legislation, leading to dramatic decreases in levels of air pollution since the time of the great smogs, a large body of epidemiological evidence has demonstrated that pollution continues to have adverse effects on human health. One striking finding from the epidemiological data is that patients with cardiovascular disease are susceptible to acute rises in ambient pollutants. Mortality and hospital admissions for myocardial infarction, congestive cardiac failure and cardiac arrhythmia all increase with a rise in the concentration of both particulate and gaseous pollutants. Before concluding that this association is a causal one, plausible pathophysiological mechanisms are required. Evidence is accumulating in support of two mechanistic hypotheses: inhalation of pollutants might provoke a local inflammatory response with the consequent release into the circulation of pro-thrombotic and inflammatory cytokines. A systemic response of this nature would put individuals with coronary atheroma at increased risk of cardiac events; exposure to pollutants may have an adverse effect on cardiac autonomic control, leading to an increased risk of arrhythmia in susceptible patients. Clarification of the pollutants involved and the precise mechanisms of action is essential in designing measures by which susceptible individuals might be protected from the adverse cardiovascular effects of air pollution.

HEALTH EFFECTS OF DIESEL EXHAUST IN ASTHMATIC PATIENTS: A REAL-WORLD STUDY IN LONDON

ISEE-210 Introduction: Epidemiological evidence suggests a link between respiratory morbidity and urban fine particulates, many of which are produced by diesel-powered vehicles. Aim: We studied the direct health effects of diesel exhaust on humans exposed within a ‘natural chamber’. Methods: On separate occasions, non-smoking adult asthmatics were exposed, for 2 hours, in Oxford Street, London (where only pedestrians, diesel powered buses and taxicabs are permitted) or Hyde Park, a large, nearby open park free of vehicles. We measured PM 2.5, elemental carbon, NO2 and ultrafine particulates during each session. Lung function and symptoms were monitored during exposures and for 24 hours after. Results: Measurements showed daytime concentrations of elemental carbon (EC) on Oxford Street are approximately 5 times higher than in Hyde Park. There were significant differences in measured concentrations of particulate pollution between exposure sites (UFP concentration (gravimetric mean). Initial analyses showed that the lung function (FEV1 and FVC) decreased from baseline at both exposure sites; this decrement was largest and more sustained following active exposure. Active exposure was also associated with increased symptoms. Conclusion: Initial analyses of this study suggests that asthmatic subjects exposed to ambient urban levels of diesel exhaust, in a natural environment, incur worsening respiratory function and symptoms that increase as particulate concentrations rise.

Roadside Concentration of Gaseous and Particulate Matter Pollutants and Risk Assessment in Dar-Es-Salaam, Tanzania

This study used manual air sampling method to assess the contribution of road traffic to air pollution level in Dar-es-Salaam City, Tanzania. Samples were collected from 11 different sites. Parameters measured were: sulphur dioxide using pararosaniline method, nitrogen dioxide using saltzman method, particulate matter and particulate lead using filtration method and atomic absorption spectrometric method, respectively. Results showed that hourly average sulphur dioxide concentration range from 127 to 1385 microg/m3. The measured values of sulphur dioxide were above the recommended WHO guidelines with an hourly objective value of 350 microg/m3 at 87% of the sampling sites. The hourly average nitrogen dioxide concentration ranged from 18 to 53 microg/m3. The maximum hourly nitrogen dioxide concentration at 53 microg/m3 was below the WHO guideline value of 200 microg/m3. The hourly average suspended particulate matter (SPM) ranged from 98 to 1161 microg/m3, exceeding the recommended value of 230 microg/m3 by WHO at 87% of the sampling sites. The hourly average lead concentration was found to range from 0.60 to 25.6 microg/m3, exceeding again the WHO guideline value of 1.5 microg/m3 at 83% of the sampling sites. Results predicted by Gaussian model when compared with the measured values were found to have a correlation coefficient of 0.8, signifying a good correlation. The risk assessment was undertaken considering the people who spend a significant portion of their time near the roads, such as the Uhuru primary school pupils and the adult population who reside by the roadside. The unit risk realised was 18.2 x 10(-6) for adult population and 2.2 x 10(-6) for pupils, both scenarios showing risk higher than the United Sates of America Environmental Protection Agency (USEPA) acceptable limit of 1 x 10(-6). Considering the magnitude of the problem at hand, this study recommends an introduction of mandatory emission tests of SPM, lead and sulphur dioxide (SO2). The study further recommends the introduction of continuous and/or regular air quality monitoring and the use non-leaded petrol in Tanzania.

Biologically plausible particulate air pollution mortality concentration-response functions.

In this article I introduce an alternative method for estimating particulate air pollution mortality concentration-response functions. This method constrains the particulate air pollution mortality concentration-response function to be biologically plausible--that is, a non-decreasing function of the particulate air pollution concentration. Using time-series data from Cook County, Illinois, the proposed method yields more meaningful particulate air pollution mortality concentration-response function estimates with an increase in statistical accuracy.

Gaseous and particulate air pollution in the Lanzhou Valley, China

Gaseous and particulate matter measurements were performed from January 1999 to December 2001 to assess seasonal and diurnal patterns of air pollutions in the Lanzhou Valley, China. The objectives are the determination of the temporal variability of total suspended particulate (TSP) matter and PM 10 levels, and their relationship with the SO 2 and NO x emissions and desert dust intrusions from the dust sources in the Hexi Corridor in Gansu Province. The results showed that concentrations of gaseous and particulate pollutants undergo seasonal variations characterized by a winter maximum levels for SO 2 (0.094–0.208 mg/m 3) and NO 2 (0.068–0.089 mg/m 3) and a spring maximum levels for TSP (0.885–1.037 mg/m 3). Linear regression analysis indicated that the diurnal mean TSP/PM 10 ratio may approximate to 3.0, and that the annual NO 2/NO x ratio was approximately 0.86, with its highest monthly average of 0.91 in June and its lowest monthly average of 0.788 in January. The origin of PM 10 episodes was investigated by correlating the PM 10 episodes in the Lanzhou Valley with the high wind speeds in Jinchang (dust sources) in the Hexi Corridor, and also, by comparing the PM 10 levels with the SO 2 and NO x concentrations. Most of the ‘high PM 10 episodes’ (1-h mean maximum >1.0 mg/m 3) were attributed to the desert dust intrusions from the Hexi Corridor. The influence of the industrial and domestic emissions in the PM 10 levels was evidenced during most of the periods with the PM 10 levels less than 1.0 mg/m 3.

On the Relation between Seasonal Synoptic Circulation Types and Spatial Air Quality Characteristics in Athens, Greece

The impact of weather on air pollution was examined and evaluated for the city of Athens, Greece. We used an objectively defined synoptic classification scheme consisting of six summer and eight winter circulation types. This scheme was established using a combination of both factor and cluster analysis during 1954–1999. Surface and isobaric levels of 850 hPa data were used. Factor analysis combined with cluster analysis was used to derive circulation types based on surface meteorological data for the period 1954–1999 in Athens and on surface pressure grid data. The city was divided into three sectors according to the financial and social activities of the residents. To examine the spatial characteristics of pollutant concentrations over Athens for each synoptic type, the synoptic circulation types were then correlated with both gaseous and particulate pollutant concentrations measured in each sector between 1983 and 1999. Finally, extreme and severe episodic events were studied in terms of their meteorological and synoptic characteristics.

The influence of meteorological conditions on the behavior of pollutants concentrations in São Paulo, Brazil

The observed behavior of pollution concentrations to the prevailing meteorological conditions has been studied for the period from June 13 to September 2, 1994, for the Metropolitan Area of Sao Paulo (MASP). The synoptic conditions, which prevailed during the period, have been identified. The behavior of these large-scale systems namely the relative positions, the nature and the types of the anticyclone or cold front (CF) has been investigated, and for each identified synoptic situation, trace elements concentrations have been determined. During the CF synoptic condition, the elements presented low concentrations associated with intense ventilation, precipitation and high relative humidity. It is seen that for both the synoptic conditions namely the South Atlantic Subtropical High and Polar High, high values of concentrations prevailed due to weak ventilation, low relative humidity and absence of precipitation. The micro and mesoscale meteorological conditions have also been studied for a day with low and a day with high concentration of particulate pollutants. Finally, applying receptor modeling to the fine aerosol mass concentration data set, five categories of emission sources in the MASP were identified: vehicles, garbage incineration, vegetation, suspend soil dust and burning of fuel oil.

Investigation of factors which might indicate susceptibility to particulate air pollution

OBJECTIVESTo determine whether previous symptoms or recognised risk factors of cardiovascular ill health, are associated with an increased likelihood of adverse health effects related to particulate air pollution.METHODSCardiovascular event rates...

Molecular characterization of smoke from campfire burning of pine wood (Pinus elliottii)

Although campfires are typically enjoyable events, people are exposed to high concentrations of gaseous and particulate pollutants. The combustion conditions of wood burned in campfires are different from those of indoor wood burning in stoves or fireplaces. Typically, wood logs, twigs, and branches with their leaves or needles are burned in campfires, whereas mostly wood logs are burned in indoor settings. Consequently, the molecular source profiles for organic particulate matter emissions may be different from a campfire. For human exposure assessment, there is a need to fingerprint the organic compound compositions in campfire wood smoke. Here we present the detailed biomarker composition of conifer wood smoke from a campfire. The major biomarkers emitted are dehydroabietic acid, the resin acids (pimaric, iso-pimaric, sandaracopimaric and abietic acids), retene, pimanthrene, methylcyclopentenophenanthrene and β-sitosterol, with levoglucosan and lignin phenolics such as vanillic acid in the polar fraction. PAH are minor components. A marker and PAH profile has been generated which can be utilized for tracing emissions from campfire burning and evaluating personal exposure risk.

Transport of ozone and pollutants from North America to the North Atlantic Ocean during the 1996 Atmosphere/Ocean Chemistry Experiment (AEROCE) intensive

Research flights were conducted to investigate the episodic occurrence of enhanced ozone mixing ratios over the North Atlantic Ocean (NAO) during the spring as part of the Atmosphere/Ocean Chemistry Experiment (AEROCE). We measured meteorological variables, trace gases, and aerosol light scattering from the University of Wyoming King Air research aircraft during 16 research flights in April and early May 1996. The flights were conducted over eastern North America and over the NAO between the United States and Bermuda. On April 28, a cold front was located just west of Bermuda while a second system developed over the Midwest and central United States. In the midtroposphere, polluted layers with up to 250 ppbv CO, 150 pptv NO, and 1.8 ppbv NOy were observed within a deeper layer of enhanced O3 mixing ratios (up to 88 ppbv) over the NAO at around 32°N, 64–68°W. These aircraft observations, when coupled with ozone sondes, back trajectories, and satellite image loops, indicate two distinct meteorological mechanisms that combine to yield the observed chemical signature of the air. There is substantial meteorological evidence, supported by ozone sonde observations and earlier King Air flights, indicating that stratosphere/troposphere exchange associated with the upstream frontal system injects and advects dry, ozone‐rich air into midtropospheric regions over the continent. These subsiding air masses have the potential to result in deep layers of enhanced ozone in the offshore postfrontal area. Convection from the developing (upwind) system appears to lift air from the continental boundary layer into the area of subsidence in the mid to upper troposphere. The result is high concentrations of gaseous and particulate pollutants along with elevated quantities of ozone. Ozone mixing ratios exceed those attributable to boundary layer venting or in‐transit photochemical production. These meteorological processes lead to pollution and enhanced ozone from the stratosphere cooccurring in postfrontal air masses over the NAO.

Chlorine loss from marine aerosol in a coastal atmosphere

The horizontal gradient concentrations of particulate and gaseous pollutants were measured on the western coast of the Iberian Peninsula. In summer, a large fraction of particulate sea‐salt chlorine (67% for fine particles and 24% for coarse particles) is already lost during the sea breezes by the time marine air masses arrive to the coast. The volatilization values increase to 86% and 68%, 30 km inland. Acidic sulphur compounds are responsible for 64–71% of the degassing of Cl from fine particles, while nitric acid is the main cause of the coarse particles, contributing with 60‐68% for the particulate chlorine loss. There is more or less an 11% chlorine degassing per hour during the air mass transport inland. Thermodynamic equilibrium is not attained during the first 3 hours of aerosol transport inland for both fine and coarse sea‐salt particles.

Air pollution and respiratory health among children with asthmatic or cough symptoms.

During the winter of 1994, the association between daily changes in air pollution and in the respiratory health of children 7 to 12 yr of age were studied in Kuopio, Finland. Seventy-four children with asthmatic symptoms and 95 children with cough only, living either in urban or suburban areas, were followed for 3 mo. During the study period, the mean daily concentration of particulate air pollution (PM10) was 18 micrograms/m3 in the urban area and 13 micrograms/m3 in the suburban area. Lagged concentrations of PM10, black smoke, and NO2 were significantly associated with declines in morning peak expiratory flow (PEF) among asthmatic children. The regression coefficient (x10) for a 2-d lag of PM10 was -0.911 (SE, 0.386) in the urban and -1.05 (0.596), in the suburban area. Among children with cough only, PM10, black smoke, and NO2 were not significantly associated with PEF. In the urban area, there was a significant association between SO2 and morning and evening PEF and incidence of upper respiratory symptoms among children who cough only. No other associations between air pollution and evening PEF or respiratory symptoms were observed. This study suggests that particulate air pollution is associated with respiratory health, especially among children with asthmatic symptoms.