Peak PM2 Research Articles

Mesoscale controls on particulate matter pollution for a mega city in a semi-arid mountainous environment: Tehran, Iran

Tehran, the mega-city capital of Iran, suffers from high concentrations of PM10 throughout the year. Emissions from transport combined with mesoscale atmospheric features related to the mountainous terrain lead to a distinctive diurnal pattern in concentrations. Air quality data from monitoring stations show that the highest concentrations of PM10 are in the morning and evening periods, associated with peak traffic volumes and transition in local meteorology from a stable nocturnal down-slope flow to a daytime upslope regime. There is a clear north-south gradient in PM10 associated with the transport by down-slope winds. A year-long simulation with The Air Pollution Model (TAPM) confirms the mesoscale meteorological regime over Tehran. Simulation results indicate that the peaks in traffic flow and the transition between meteorological regimes contribute to daily PM10 peaks, with the transition playing a relatively minor role.

Temperature, comfort and pollution levels during heat waves and the role of sea breeze

During the summer of 2007 several Greek regions suffered periods of extreme heat, with midday temperatures of over 40 degrees C on several consecutive days. High temperatures were also recorded on the east coast of central Greece, where a complex sea breeze circulation system frequently develops. The more intense events occurred at the end of June and July. The highest temperatures were observed on 26 June and 25 July, while the sea breeze developed only on 25 July. Meteorological data collected at two sites-a coastal urban location and an inland suburban site that is not reached by the sea breeze flow-as well as pollution data collected at the urban site, were analysed in order to investigate the relationship between sea breeze development and the prevailing environmental conditions during these two heat wave events. The analysis revealed that sea breeze development affects temperature and pollution levels at the shoreline significantly, causing a decrease of approximately 4 degrees C from the maximum temperature value and an increase of approximately 30% in peak PM10 levels. Additionally, several stress indices were calculated in order to assess heat comfort conditions at the two sites. It was found that nocturnal comfort levels are determined mainly by the urban heat island effect, the intensity of which reaches up to 8 degrees C, while the applied indices do not demonstrate any significant daytime thermal stress relief due to sea breeze development.

Assessment of vertically-resolved PM<sub>10</sub> from mobile lidar observations

Abstract. We investigate in this study the vertical PM10 distributions from mobile measurements carried out from locations along the Paris Peripherique (highly trafficked beltway around Paris), examine distinctions in terms of aerosol concentrations between the outlying regions of Paris and the inner city and eventually discuss the influence of aerosol sources, meteorology, and dynamics on the retrieved PM10 distributions. To achieve these purposes, we combine in situ surface measurements with active remote sensing observations obtained from a great number of research programs in Paris area since 1999. Two approaches, devoted to the conversion of vertical profiles of lidar-derived extinction coefficients into PM10, have been set up. A very good agreement is found between the theoretical and empirical methods with a discrepancy of 3%. Hence, specific extinction cross-sections at 355 nm are provided with a reasonable relative uncertainty lower than 12% for urban (4.5 m2 g−1) and periurban (5.9 m2 g−1) aersols, lower than 26% for rural (7.1 m2 g−1) aerosols, biomass burning (2.6 m2 g−1) and dust (1.1 m2 g−1) aerosols The high spatial and temporal resolutions of the mobile lidar (respectively 1.5 m and 1 min) enable to follow the spatiotemporal variability of various layers trapping aerosols in the troposphere. Appropriate specific extinction cross-sections are applied in each layer detected in the vertical heterogeneities from the lidar profiles. The standard deviation (rms) between lidar-derived PM10 at 200 m above ground and surface network stations measurements was ~14μg m−3. This difference is particularly ascribed to a decorrelation of mass concentrations in the first meters of the boundary layer, as highlighted through multiangular lidar observations. Lidar signals can be used to follow mass concentrations with an uncertainty lower than 25% above urban areas and provide useful information on PM10 peak forecasting that affect air quality.

Double Trouble: Flu Intensifies Effects of Ozone

Vol. 117, No. 2 EnvironewsOpen AccessDouble Trouble: Flu Intensifies Effects of Ozone Cynthia Washam Cynthia Washam Search for more papers by this author Published:1 February 2009https://doi.org/10.1289/ehp.117-a74bCited by:1AboutSectionsPDF ToolsDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InReddit Environmental health scientists have long speculated that the influenza virus could intensify the pulmonary effects of air pollution or vice versa. Like air pollution, influenza affects primarily the respiratory system, and ambient air pollutants may either lower resistance to viral infection or provide a vehicle that facilitates the spread of the virus, or both. There have been a number of laboratory-based animal studies on this potential relationship but no epidemiologic research. Researchers at the University of Hong Kong, in the first study of the influenza–air pollution interaction in humans, now report that respiratory hospitalizations and mortality significantly increased when ozone (O3) levels rose during flu season [EHP117:248–253; Wong et al.].The authors conducted a retrospective population-based study focusing on hospitalization and mortality rates for respiratory and cardiovascular disease. Medical data on patients diagnosed with respiratory or cardiovascular disease between 1996 and 2002 came from 14 Hong Kong hospitals. The authors determined “influenza intensity” during the same period as the percentage of respiratory specimens that tested positive for influenza each week. The Hong Kong Environmental Protection Department provided data on average daily concentrations of nitrogen dioxide (NO2), sulfur dioxide (SO2), particulate matter smaller than 10 μm (PM10), and O3.As O3 levels increased during times of high influenza intensity, so did the number of hospitalizations and deaths from respiratory disease. The association was stronger in women than men, the researchers reported. There was no significant relationship between O3 and cardiovascular disease hospitalizations or mortality, and the data reflected no significant modification by influenza on the health effects of the other pollutants studied. Hong Kong has two flu seasons, peaking in January–February and May–July. O3 levels in Hong Kong typically peak in the sunniest months of September–December, when ultraviolet radiation reacts with nitrogen oxides and volatile organic compounds to form the noxious gas.A surprising finding was a decrease in hospitalization for respiratory illness when peak PM10 concentrations coincided with flu outbreaks, whereas PM10 increases at other times were associated with increased hospitalizations. The researchers hypothesize that PM10 may diminish the flu effect by limiting the amount of ultraviolet light entering the atmosphere, which in turn would reduce the production of ozone.The authors found weak interactions between influenza and both NO2 and SO2, but cautioned against drawing conclusions about individual pollutants that react in the atmosphere. NO2, for example, can combine with oxygen to form O3. The researchers propose that future studies focus on influenza’s potential interactions with a combination of pollutants in the atmosphere.Influenza appeared to exacerbate the health effects of ozone pollution in Hong Kong.FiguresReferencesRelatedDetailsCited by Sloan C, Moore M and Hartert T (2011) Impact of Pollution, Climate, and Sociodemographic Factors on Spatiotemporal Dynamics of Seasonal Respiratory Viruses, Clinical and Translational Science, 10.1111/j.1752-8062.2010.00257.x, 4:1, (48-54), Online publication date: 1-Feb-2011. Vol. 117, No. 2 February 2009Metrics About Article Metrics Publication History Originally published1 February 2009Published in print1 February 2009 Financial disclosuresPDF download License information EHP is an open-access journal published with support from the National Institute of Environmental Health Sciences, National Institutes of Health. All content is public domain unless otherwise noted. Note to readers with disabilities EHP strives to ensure that all journal content is accessible to all readers. However, some figures and Supplemental Material published in EHP articles may not conform to 508 standards due to the complexity of the information being presented. If you need assistance accessing journal content, please contact [email protected]. Our staff will work with you to assess and meet your accessibility needs within 3 working days.

Acute exposure to elevated PM2.5 generated by traffic and cardiopulmonary health effects in healthy older adults

There are evidences for exposure to vehicular emissions and adverse cardiopulmonary health effects. This study attempted to further explore these effects on elderly. This study monitored personal PM(2.5) concentrations and ambulatory electrocardiograms continuously for 24 h on 1 working day in 3 separate weeks for 11 school crossing guards. Spirometry was also performed before and after the morning shift. The traffic at each work location was video recorded during one of the three morning shifts. The increases in the average personal PM(2.5) concentrations (baseline PM(2.5) was subtracted) of 1.2-87 and 1.1-98 microg/m(3) were observed during the 1-h morning (DeltaPM(2.5-ave-m)) and afternoon shift (DeltaPM(2.5-ave-a)), respectively. Traffic count was not a significant predictor of the DeltaPM(2.5-ave-m) (P=0.78). Mean heart rate variability (HRV), measured as 5-min standard deviation of normal-to-normal (SDNN) beats during the 10-min rest periods, decreased 18-26% (P<0.02) 15 min, 2 and 4 h after the morning shift, but changes in SDNN (DeltaSDNN) were insignificant post-afternoon exposure (-0.3 to -7% with P>0.53). DeltaSDNN were negatively associated with DeltaPM(2.5-ave-m), with the strongest association at 2 h after the morning shift (P<0.01) but insignificant 4 h after the morning exposure. The peak PM(2.5) concentration (DeltaPM(2.5-peak), baseline PM(2.5) was subtracted) was not a significant predictor for DeltaSDNN, and no clear effect of PM(2.5) exposure on heart rate was observed. There was no effect of PM exposure on lung function (P>0.16), either. In conclusion, acute exposure to the PM(2.5) resulting from mobile sources can cause acute decline in HRV in healthy older adults, suggesting one of the biological mechanisms for the adverse cardiovascular health effects associated with traffic-related air pollution. Traffic count may not be an appropriate surrogate measure of acute personal exposure to vehicular emission in traffic congested areas.

Chemical characterization of fine particulate matter during peak PM10 episodes in Apulia (South Italy)

Some peak PM10 episodes, occurred during PM monitoring campaigns performed on October 2005 and February and June 2006 in Bari town, have been characterized. Moreover back trajectories of air masses and Principal Component Analyses were applied. Three of the peak PM10 episodes investigated were related to local emissions of primary pollutants during poor atmospheric dispersion conditions. The other two peak PM10 episodes considered are related with long range transport air masses toward Apulia region: in one case the chemical characterization and the back trajectories analysis indicate that high PM10 value detected is due to the Saharan dust advection in the Apulia region; in the other case air masses with different origin give rise to high PM10 value. Moreover PM10 daily mean concentrations, presented in this paper collected from January 2005 to August 2007 and obtained by automatic device in six stations of air quality monitoring networks in Bari territory, do not show a seasonal trend for PM10 concentrations, contrary to the PM10 trend shown in the towns of North Italy. This can be explained mostly considering that our region presents generally meteo-climatic conditions that favour pollutants dispersion.

Internal friction study of oxygen ion conductors La1.95K0.05Mo2−xTxO9−δ (T=Fe,Mn)

Based on the oxygen ion conductor La2Mo2O9, a series of K, Fe, and Mn doped samples La1.95K0.05Mo2−xTxO9−δ (T=Fe,Mn; x=0,0.025,0.05,0.1) were prepared with conventional solid-state reaction method. The effects of Fe and Mn doping on the cationic and anionic ions diffusion, phase transition, and electrical conductivity were studied. The mechanical spectroscopy (or internal friction) technique was exploited to investigate the microscopic transport mechanism and to deduce the dynamical relaxation parameters. Three internal friction peaks (PL, PH, and PM) were observed in the La1.95K0.05Mo2−xTxO9−δ samples, among which PL and PM are of relaxational type while PH is associated with a kind of phase transition. The results revealed that peak PL is originated from the short-distance jumps of oxygen vacancies, while peak PM is associated with the short-distance diffusion of Mn (Fe) ions and peak PH with the phase transition from the static disordered state to the dynamic disordered state of oxygen ion distribution. Based on the results of conductivity measurements, it can be concluded that the high-temperature conductivity of La2Mo2O9 can be improved obviously by the Fe or Mn doping at Mo site and the low-temperature conductivity can be increased by the simultaneous K doping at La site.

Long-range transport of Asian dust and air pollutants to Taiwan: observed evidence and model simulation

Abstract. Long-range transport of Asian dust and air pollutants are major environmental concerns of Taiwan during the winter monsoon season when northeasterly winds prevail following passages of cold fronts. Based on hourly measurements of Taiwan Environmental Protection Administration (TEPA) air quality monitoring stations, Lidar and in-situ IC, a significant long-range transport dust and air pollutants event on 18 March 2005 has been identified. During this episode, drastically elevated concentrations of PM10, CO and SO2 along with the strong northeasterly on 18 March were observed over background Wanli station, with peaks of about 170 μgm−3, 1.0 ppm and 14 ppb, respectively. We have found that air masses of air pollutants and Asian dust are transported separately. Although the mixing takes place on the way to Taiwan, it mixes slightly when they arrived in Taiwan. The major component of the first PM10 peak were air pollutants, evidenced by the consistent peaks of SO42− and NO3

Acute Short-Term Exposures to PM2.5 Generated by Vehicular Emissions and Cardiopulmonary Effects in Older Adults

TM6-O-06 A pilot study was conducted to examine the impact of acute exposure to PM2.5 generated by vehicular emissions on changes in heart rate variability (HRV) and lung function in healthy older adults (mean age, 62 years), school crossing guards in Paterson, NJ. Each subject wore a real-time PM2.5 monitor and a cardiac Holter monitor for 24 hours on 1 working day in 3 separate weeks. Spirometry was performed prior to and after the morning shift, and at the end of monitoring session (24 hours). Traffic information for each working location was video recorded during the morning shift. Exposure to elevated PM2.5 was observed for school crossing guards during their morning shift, with the 1-hour average PM2.5 levels of 12 to 80 μg/m3 and the 1-minute peak PM2.5 concentrations of several hundred μg/m3. The 1-hour average morning PM2.5 was much higher (1–19 times) than that in the afternoon shift due to higher motor vehicle emissions from the morning rush-hour traffic. In addition, the pilot study suggested that the use of traffic count may underestimate the exposure to air pollutants generated by motor vehicle emissions in areas where the average speed is very low and the vehicles are often stopped. This is because vehicles idled while stopped, but they continued emitting air pollutants but did not increase the traffic count. The association between change in lung function and increased PM was explored by a mixed-effect model with controlled for gender, age, and smoking status. A subtle decrease in FEV1 (decrease in 0.019 L per increase of 10 μg/m3 PM2.5) was observed right after the morning shift with increased PM2.5 levels (P = 0.07). The changes in HRV right after exposure, 2 and 4 hours after exposure, were calculated and compared with the increased PM during the morning shift. No significant association was found between elevated PM2.5 levels and the change of HRV measured right after and 4 hours after the morning shift. However, the change in HRV obtained at 2 hours after exposure was negatively associated with elevated PM2.5 levels (slope = −0.22, P = 0.019). The preliminary data obtained from our pilot study provide evidence that short-term acute exposure to vehicular emissions resulted in changes in HRV and lung function. Moreover, the pilot study demonstrated that it is feasible to study cardiovascular and pulmonary effect on active and healthy older adults in a real world situation.

Influence of Asian dust storms on air quality in Taiwan

In each year, dust storms triggered by cold air masses passing through northern China and Mongolia enhance the PM10 concentration over Taiwan region during winter and spring. On average, there are four to five dust events and 6.1 dust days in a year in Taiwan. Each event lasts for 1 day or even longer. A procedure to identify a dust event is rationalized and exercised on data collected during 1994–2005. Also, a ranking method named as the dust intensity rank (DIR) is developed to distinguish the intensity of each event affecting the local air quality. About 86% of dust days belong to ranks 1 and 2. In general, poorer air quality is associated with higher ranks. Ranks 4 and 5 correspond to a PSI (Pollution Standard Index) larger than 100. Linking DIR with the popular PSI is useful for both the public and the official forecasting system. It is also useful for inter-comparison between dust influences on air quality at different downstream regions in Taiwan. Composite analyses of the temporal and spatial variation of the hourly PM10 level indicate that dust particles usually arrive 12 h before the time of the peak PM10 concentration and last for 36 h at northern Taiwan, while the time of the peak concentration at eastern or western Taiwan, due to the evolution of the synoptic weather system, is about 3–12 h later. It is noted that the increase of PM10 level at the western side of Taiwan results from a mixture of upstream Asian dust inputs and local pollutants.

Speciation and sources of atmospheric aerosols in a highly industrialised emerging mega-city in Central China

Monitoring air quality in large urban agglomerations is the key to the prevention of air pollution-related problems in emerging mega-cities. The city of Wuhan is a highly industrialised city with >9 million inhabitants in Central China. Simultaneous PM10 sampling was performed during 1 year at one urban and one industrial site. Mean PM10 daily levels (156 microg m(-3) at the urban site and 197 microg m(-3) at the industrial hotspot) exceed the US-EPA or EU annual limit values by 3-4 times. A detailed study of daily speciation showed that the mean chemical composition of PM10 presents minimal differences between peak and low PM episodes. This implies that PM10 aerosols in the study area result from local emissions, and air quality management and abatement strategies in Wuhan should thus focus on local anthropogenic sources. The levels of some elements of environmental concern are relatively high (409-615 ngPb m(-3), 66-70 ngAs m(-3), 116-227 ngMn m(-3), 10-12 ngCd m(-3)) due to industrial, but also urban emissions. Principal component analysis identified a mineral source (probably cement and steel manufacture) and smelting as the main contributors to PM10 levels at the industrial site (34%), followed by a coal fired power plant (20%) and the anthropogenic regional background (16%). At the urban site the major PM10 source is a mixed coal combustion source (31%), followed by the anthropogenic regional background (28%) and traffic (16%).

Modeling wind-blown desert dust in the southwestern United States for public health warning: A case study

A model for simulating desert dust cycle was adapted and applied for a dust storm case in the southwest United States (US). This is an initial test of the model's capability as part of a future public health early warning system. The modeled meteorological fields, which drive a dust storm, were evaluated against surface and upper-air measurement data. The modeled dust fields were compared with satellite images, in situ surface PM2.5 and PM10 data, and visibility data in the areas affected by the dust event. The model predicted meteorological fields reasonably well. The modeled surface and upper-air field patterns were in agreement with the measured ones. The vertical profiles of wind, temperature, and humidity followed closely with the observed profiles. Statistical analyses of modeled and observed meteorological variables at surface sites showed fairly good model performance. The modeled dust spatial distributions were comparable with the satellite-observed dust clouds and the reduced visibility patterns. Most encouragingly, the model-predicted and observed PM2.5 peak hours matched reasonably well. The model produced better PM2.5 peak hours than PM10 peak hours. The temporal varying trends of daily and hourly PM2.5 and PM10 concentrations at most of the measurement sites were similar to those observed. Discrepancies between the values of the modeled and the measured surface PM2.5 and PM10 concentrations differed with time and location. Sometimes the modeled and measured concentrations can have one order of magnitude differences. These revealed there were possible deficiencies in the simulation of the dust production strength and location, and the representation of dust particle size in the modeling. Better land surface data and size representation of the dust production are expected to further improve model performance.

The Impact of a Building Implosion on Airborne Particulate Matter in an Urban Community

In response to community concerns, the air quality impact of imploding a 22-story building in east Baltimore, MD, was studied. Time- and space-resolved concentrations of indoor and outdoor particulate matter (PM) (nominally 0.5–10 µm) were measured using a portable nephelometer at seven and four locations, respectively. PM10 levels varied in time and space; there was no measurable effect observed upwind of the implosion. The downwind peak PM10 levels varied with distance (54,000–589 µg/m3) exceeding pre-implosion levels for sites 100 and 1130 m 3000- and 20-fold, respectively. Estimated outdoor 24-hr integrated mass concentrations varied from 15 to 72 µg/m3. The implosion did not result in the U.S. Environmental Protection Agency (EPA) National Ambient Air Quality Standard (NAAQS) for PM10 being exceeded. X-ray fluorescence analysis indicated that the elemental composition was dominated by crustal elements: calcium (57%), silicon (23%), aluminum (7.6%), and iron (6.1%). Lead was above background but at a low level (0.17 µg/m3). Peak PM10 concentrations were short-lived; most sites returned to background within 15 min. No increase in indoor PM10 was observed even at the most proximate 250 m location. These results demonstrate that a building implosion can have a severe but short-lived impact on community air quality. Effective protection is offered by being indoors or upwind.

Evaluating the first‐order effect of intraannual temperature variability on urban air pollution

The direct effect of intraannual temperature variability on ozone and PM2.5 concentrations at the urban scale was simulated using a high‐resolution air quality model that tracks the temperature‐dependant formation of secondary organic and inorganic aerosol components. Calculations show that the concentration of ozone and non‐volatile secondary particulate matter will generally increase at higher temperatures due to increased gas‐phase reaction rates. The concentration of semi‐volatile reaction products also will increase at higher temperatures, but the amount of this material that partitions to the particle‐phase may decrease as equilibrium vapor pressures rise. Calculations performed for Southern California on September 25, 1996 predict that intraannual temperature variability may cause peak ozone and PM2.5 concentrations to fluctuate by up to 16% and 25% respectively. 24‐hour average PM2.5 concentrations will decrease with increasing temperatures for inland portions of the South Coast air basin during most of the day. Slight increases in 24‐hour average PM2.5 concentrations were predicted for coastal regions. The majority of the predicted shift in PM2.5 concentrations was related to increased production rates for nitric acid and condensable organic compounds balanced against increased volatilization of these products. Semi‐volatile particulate ammonium nitrate concentrations are most sensitive to volatilization losses at hotter temperatures and when the ratio of gas‐phase ammonia to nitric acid concentrations is approximately unity. Background sulfate particles and particles released from non‐catalyst equipped gasoline‐powered engines, diesel engines, and food cooking were shifted to smaller sizes as ammonium nitrate volatilized at hotter temperatures.

Study on Low Frequency Internal Friction for Pb(Zr,Ti)O3 Ferroelectric Ceramics

The internal friction Q–1 and the square of vibration frequency f2 (proportional to shear modulus G) were measured as functions of temperature on undoped Pb(Zr0.7Ti0.3)O3 (PZT73) and Pb(Zr0.3Ti0.7)O3 (PZT37) ceramics from 20 to 500 °C. Experiments were performed on an inverted torsion pendulum at low frequencies (0.1 to 5 Hz). Two internal friction peaks were found in pure rhombohedral PZT73 ceramics. The high temperature peak PM, which appears near the Curie temperature, originates from the viscous movement of domain walls. The low temperature peak P1 is a broadened Debye peak in nature, and it is attributed to the oscillation damping of the domain walls presumably acted by charged oxygen vacancies. For the pure tetragonal PZT37 ceramics, another peak P2, which appears between P1 and PM, can be well described by the coupling model. It is thought to be caused by the relaxation of oxygen vacancy clusters near the 90° domains.

Respiratory function as measured by peak expiratory flow rate and PM10: six communities study.

This Six Communities Study conducted at six communities in southwestern North Carolina investigates the respiratory health status of residents whose households are located near an incinerator. This diary study makes it possible to estimate the daily variation of pulmonary function measured as peak expiratory flow rate (PEFR) related to 24-h mean PM10 levels, which were observed at each monitoring station placed in the six study communities, as a surrogate exposure measure of outdoor air pollution. Observations of PEFR among participants in each community were analyzed to determine how they varied according to the degree of exposure to ambient pollutants as well as to other cofactors including, sex, age, respiratory hypersensitivity, hours spent outdoors within the area of the selected community, and surrogate measures for indoor air pollution exposure (vacuum use and experience of air irritants at work). The findings revealed that respiratory hypersensitivity status is a predictor of declining PEFR. PM10 concentrations measured in each study area did not seem to be related to the variations of respiratory health as measured by PEFR. This study did not show any difference in respiratory health between subjects of an incinerator community and those of its comparison community. Even though this community-based study with free-living subjects shows negative findings on the relationship between respiratory health and PM10, it is worth noting that these findings must be interpreted cautiously because exposure estimation based on monitoring of ambient air likely results in misclassification of true exposure levels.

Carrier effect on structure and properties of heat-treated poly(ethylene terephthalate) fibers. I. Thermal analysis and dynamic mechanical properties

Poly(ethylene terephthalate) (PET) fibers of different draw ratios (as spun and drawn 2.8×) were submitted to different heat settings. Subsequently, they were treated in benzoic acid solutions at different concentrations and for different times of exposition. The plas-ticizing effect on the morphology of these heat-setted fibers due to the different treatments in benzoic acid solutions was studied by differential scanning calorimetry (DSC) and dynamic and mechanical thermal analysis (DMTA). The DSC experiments revealed the appearance of a premelting peak (pm1) around 130°C, when the applied heat settings were carried out for 8 h in the presence of boiling water, and around 150–160°C for the dry heat setting for 7 h at 130°C followed by 1 h in the presence of boiling water. These premelting peaks have been associated with the melting of smaller and imperfect crystals present in the amorphous region. Also, the analysis of the main melting peaks revealed that the undrawn fiber presented a wider distribution of smaller crystals than the drawn one. Their subsequent treatments in the benzoic acid solutions revealed through the DSC thermograms that this first premelting peak tends to disappear as the concentration and time of benzoic acid treatment increase. Also, a new premelting peak (pm2) appears in the DSC thermograms at temperature around 180°C. It seems that a dislocation of the pm 1 peak is occurring towards higher temperatures and is being transformed in this new premelting peak. The DMTA revealed the appearance of an αc transition in the temperature range from 140 to 160°C and this αc transition seems to be related to the relaxations of the new crystallities formed due to the plasticization effect of the benzoic acid. Also, the second premelting peak seems to be related to the fusion of such crystals. Therefore, a complex change in the morphology of the studied PET fibers due to the benzoic acid action has been revealed. © 1996 John Wiley & Sons, Inc.

Acute health effects of PM10 pollution on symptomatic and asymptomatic children.

This study assessed the association between daily changes in respiratory health and respirable particulate pollution (PM10) in Utah Valley during the winter of 1990-1991. During the study period, 24-h PM10 concentrations ranged from 7 to 251 micrograms/m3. Participants included symptomatic and asymptomatic samples of fifth- and sixth-grade students. Relatively small but statistically significant (p less than 0.01) negative associations between peak expiratory flow (PEF) and PM10 were observed for both the symptomatic and asymptomatic samples. The association was strongest for the symptomatic children. Large associations between the incidence of respiratory symptoms, especially cough, and PM10 pollution were also observed for both samples. Again the association was strongest for the symptomatic sample. Immediate and delayed PM10 effects were observed. Respiratory symptoms and PEF changes were more closely associated with 5-day moving-average PM10 levels than with concurrent-day levels. These associations were also observed at PM10 levels below the 24-h standard of 150 micrograms/m3. This study indicates that both symptomatic and asymptomatic children may suffer acute health effects of respirable particulate pollution, with symptomatic children suffering the most.

Altered regulation of adrenal steroidogenesis in 2,3,7,8-tetrachlorodibenzo- p-dioxin-treated rats

A single treatment of 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) (50 μg/kg) produced two distinct effects on adrenal steroidogenesis in rats 13 days post-treatment. In unstressed rats, the very low corticosterone levels early in the light phase (AM) increased 4-fold relative to ad libitum-fed control (ALC) rats, but the peak level of corticosterone that is seen late in the light phase (PM) decreased up to 40% relative to ALC rats. The AM stimulation was also observed in rats pair-fed to compensate for the diminished feed intake of TCDD-treated animals, indicating that the change results from nutritional deprivation. The PM suppression, however, was not observed in pair-fed rats. In rats given a lower dose of TCDD (15 μg/kg), there was no AM stimulation, whereas the suppression of the PM diurnal peak of corticosterone was retained. Plasma adrenocorticotropin (ACTH) levels and adrenal size were not changed by these treatments, indicating that TCDD affects adrenal responsiveness. TCDD did not, however, have a significant effect on corticosterone secretion in rats receiving high doses of ACTH. In control animals, the availability of cholesterol to cytochrome P-450 scc limits the rate of steroidogenesis. While the specific content of the cytochrome was unaffected by TCDD, cholesterol turnover by this enzyme appeared to be affected following TCDD treatment, as evidenced by small increases in the mitochondrial levels of free cholesterol, reactive cholesterol, and in the proportion of P-450 scc complexed with cholesterol relative to both ad libitum- and pair-fed controls. This accumulation of mitochondrial cholesterol following TCDD treatment is consistent with an inhibition of cholesterol metabolism at cytochrome P-450 scc in vivo that is removed upon isolation of the mitochondria. These TCDD-induced increases were enhanced substantially in ACTH-stimulated rats, probably because ACTH enhances cholesterol influx into the mitochondria. Normally, substrate availability is rate limiting in cholesterol side-chain cleavage, and the AM stimulation of steroidogenesis by TCDD may result from such increased cholesterol transfer. The inhibition of cholesterol side-chain cleavage resulting from TCDD treatment may, however, only become rate limiting for corticosterone synthesis when cholesterol transfer is more substantially activated, as for peak PM secretion.