Heterogeneous HONO formation deteriorates the wintertime particulate pollution in the Guanzhong Basin, China.

Despite implementation of strict emission mitigation measures since 2013, heavy haze with high levels of secondary aerosols still frequently engulfs the Guanzhong Basin (GZB), China, during wintertime, remarkably impairing visibility and potentially causing severe health issues. Although the observed low ozone (O3) concentrations do not facilitate the photochemical formation of secondary aerosols, the measured high nitrous acid (HONO) level provides an alternate pathway in the GZB. The impact of heterogeneous HONO sources on the wintertime particulate pollution and atmospheric oxidizing capability (AOC) is evaluated in the GZB. Simulations by the Weather Research and Forecast model coupled with Chemistry (WRF-Chem) reveal that the observed high levels of nitrate and secondary organic aerosols (SOA) are reproduced when both homogeneous and heterogeneous HONO sources are considered. The heterogeneous sources (HET-sources) contribute about 98% of the near-surface HONO concentration in the GZB, increasing the hydroxyl radical (OH) and O3 concentration by 39.4% and 22.0%, respectively. The average contribution of the HET-sources to SOA, nitrate, ammonium, and sulfate in the GZB is 35.6%, 20.6%, 12.1%, and 6.0% during the particulate pollution episode, respectively, enhancing the mass concentration of fine particulate matters (PM2.5) by around 12.2%. Our results suggest that decreasing HONO level or the AOC becomes an effective pathway to alleviate the wintertime particulate pollution in the GZB.

Introductory lecture: air quality in megacities.

Urbanization is an ongoing global phenomenon as more and more people are moving from rural to urban areas for better employment opportunities and a higher standard of living, leading to the growth of megacities, broadly defined as urban agglomeration with more than 10 million inhabitants. Intense activities in megacities induce high levels of air pollutants in the atmosphere that harm human health, cause regional haze and acid deposition, damage crops, influence air quality in regions far from the megacity sources, and contribute to climate change. Since the Great London Smog and the first recognized episode of Los Angeles photochemical smog seventy years ago, substantial progress has been made in improving the scientific understanding of air pollution and in developing emissions reduction technologies. However, much remains to be understood about the complex processes of atmospheric oxidation mechanisms; the formation and evolution of secondary particles, especially those containing organic species; and the influence of emerging emissions sources and changing climate on air quality and health. While air quality has substantially improved in megacities in developed regions and some in the developing regions, many still suffer from severe air pollution. Strong regional and international collaboration in data collection and assessment will be beneficial in strengthening the capacity. This article provides an overview of the sources of emissions in megacities, atmospheric physicochemical processes, air quality trends and management in a few megacities, and the impacts on health and climate. The challenges and opportunities facing megacities due to lockdown during the COVID-19 pandemic is also discussed.

Integrated urban hydrometeorological, climate and environmental services: Concept, methodology and key messages.

Integrated Urban hydrometeorological, climate and environmental Services (IUS) is a World Meteorological Organization (WMO) initiative to aid development of science-based services to support safe, healthy, resilient and climate friendly cities. Guidance for Integrated Urban Hydrometeorological, Climate and Environmental Services (Volume I) has been developed with the intent to provide an overview of the concept, methods and good practices for producing and providing these services to respond to urban hazards across a range of time scales (weather to climate). This involves combining (dense) heterogeneous observation networks, high-resolution forecasts, multi-hazard early warning systems and climate services to assist cities in setting and implementing mitigation and adaptation strategies for the management and building of resilient and sustainable cities. IUS includes research, evaluation and delivery with a wide participation from city governments, national hydrometeorological services, international organizations, universities, research institutions and private sector stakeholders. An overview of the IUS concept with key messages, examples of good practice and recommendations are provided. The research community will play an important role to: identify critical research challenges; develop impact forecasts and warnings; promote and deliver IUS internationally, and; support national and local communities in the implementation of IUS thereby contributing to the United Nations' Sustainable Development Goals at all scales.

Aerosol-photolysis interaction reduces particulate matter during wintertime haze events.

Aerosol-radiation interaction (ARI) plays a significant role in the accumulation of fine particulate matter (PM2.5) by stabilizing the planetary boundary layer and thus deteriorating air quality during haze events. However, modification of photolysis by aerosol scattering or absorbing solar radiation (aerosol-photolysis interaction or API) alters the atmospheric oxidizing capacity, decreases the rate of secondary aerosol formation, and ultimately alleviates the ARI effect on PM2.5 pollution. Therefore, the synergetic effect of both ARI and API can either aggravate or even mitigate PM2.5 pollution. To test the effect, a fully coupled Weather Research and Forecasting (WRF)-Chem model has been used to simulate a heavy haze episode in North China Plain. Our results show that ARI contributes to a 7.8% increase in near-surface PM2.5 However, API suppresses secondary aerosol formation, and the combination of ARI and API results in only 4.8% net increase of PM2.5 Additionally, API increases the solar radiation reaching the surface and perturbs aerosol nucleation and activation to form cloud condensation nuclei, influencing aerosol-cloud interaction. The results suggest that API reduces PM2.5 pollution during haze events, but adds uncertainties in climate prediction.

Integrated urban services: Experience from four cities on different continents.

Rapid urbanization combined with climate change necessitates new types of urban services that make best use of science and technology. The Integrated Urban Hydro-Meteorological, Climate and Environmental Services and systems are a new initiative from the World Meteorological Organization (WMO) that seeks to provide science-based integrated urban services supporting safe, healthy and resilient cities. Various cities have already started development and implementation of such Integrated Urban Services and successfully test and use them following specific requirements of local stakeholders. This paper demonstrates the novel concept and approach of Integrated Urban Hydro-Meteorological, Climate and Environmental Services (IUS) from a set of four case study cities: Hong Kong, Toronto, Mexico City and Paris, that use different IUS configurations with good existing practice. These cities represent a range of countries, climates and geophysical settings. The aggregate main joint similarities of the IUS in these cities and synergy of the cities' experience, achievements and research findings are presented, as well as identification of existing gaps in knowledge and further research needs. A list of potential criteria for identifying and classifying IUS demonstration cities is proposed. It will aid future, more detailed analysis of the IUS experience, and selection of additional demonstration cities.

Construction and Operation of a Respiration Chamber of the Head-Box Type for Methane Measurement from Cattle.

This paper aims to describe the construction and operation of a respiration chamber of the head-box type for methane (CH4) measurements in bovines. The system consists of (1) a head box with a stainless steel frame and acrylic walls, floor, and ceiling; (2) a stainless steel feeder; (3) an automatic drinking water bowl; (4) a hood made from reinforced canvas; (5) an infrared (IR) CH4 gas analyzer, a mass flow generator, a data-acquisition system; and (6) a steel metabolic box. Six assays were conducted to determine the pure CH4 recovery rate of the whole system in order to validate it and comply with standards of chamber operation. The gravimetrical method was used for the recovery test and the recovery rate obtained was 1.04 ± 0.05. Once the system was calibrated, measurements of CH4 were conducted using eight animals consisting of four Holstein cows with a live weight of 593.8 ± 51 kg and an average milk yield of 23.3 ± 1.8 kg d-1 and four heifers with a live weight of 339 ± 28 kg. The CH4 production values were 687 ± 123 and 248 ± 40 L CH4 d-1 for cows and heifers, respectively. The CH4 yield was 19.7 ± 3.4 g and 17.1 ± 3.4 g CH4 kg-1 of dry matter consumed for cows and heifers, respectively. These results are consistent with those reported in the literature.

Pithecellobium dulce, Tagetes erecta and Cosmos bipinnatus on reducing enteric methane emission by dairy cows / Pithecellobium dulce, Tagetes erecta e Cosmos bipinnatus na redução de emissão de metano por vacas leiteiras

ABSTRACT: The aim of the present research was to evaluate the effect of Pithecellobium dulce, Tagetes erecta and Cosmos bipinnatus on methane emission, milk yield and dry matter intake in dairy cattle. A 4×4 Latin square experimental design was employed, using four multiparous Holstein cows of 553±72.4kg body weight, at mid lactation and average milk yield of 17.3±3kg/day. The experiment lasted 92 days, divided into four experimental periods of 23 days each. All cows had free access to maize and alfalfa silage in a 50:50 proportion, 4kg of concentrate/day and ad libitum access to water. Treatments consisted in supplementation of 0.5kg/day of the experimental plants, with one control treatment without supplementation. Each cow received one of each treatment in turn during one of the four periods. The C. bipinnatus reduced methane production by 16% (P<0,05) in comparison with the control diet. Milk production, milk composition and dry matter intake were not affected (p>0 0.05) by the use of C. bipinnatus or any other plant species. Supplementation at low doses of C. bipinnatus showed a reduction in ruminal methane production in dairy cows.

RESUMO: O objetivo deste estudo é avaliar o efeito do Pithecellobium dulce, Tagetes erecta e o Cosmos bipinnatus na emissão do metano, a produção de leite e de ingestão diária de matéria seca pelo gado. Um desenho experimental do quadrado latino 4x4 foi usado, com quatro vacas da raça Holandesa, multíparas, de 553±72,4kg, no seu segundo terço da lactação e rendimento médio de leitedo de 17,3±3kg/dia. O experimento durou 92 dias e foi dividido em quatro períodos de 23 dias cada um. Das vacas tinham acesso livre a milho e silagem de alfafa, numa proporção de 50:50, com 4kg de concentrado por dia, com acesso a água ad libitum. Os tratamentos consistiram na ingestão de 0,5kg por dia, com as plantas experimentais; as vacas no tratamento de controle não receberam nenhuma planta, porém, elas receberamum tratamento, em cada um dos quatro períodos. O C. bipinnatus reduziu significativamente a produção de metano em 16% (P<0,05), em comparação com a dieta controle. A produção de leite, sua composição e o consumo de matéria seca não foram afetados (P>0,05) pelo uso de C.bipinnatus ou outras espécies de plantas. A ingestão com doses baixas de C. bipinnatus, que é uma planta arbustiva com um centéudo moderado de taninos, mostrou ter potencial para reduzir a produção de metano ruminal em vacas leiteiras.

Real-world emissions of in-use off-road vehicles in Mexico.

Off-road vehicles used in construction and agricultural activities can contribute substantially to emissions of gaseous pollutants and can be a major source of submicrometer carbonaceous particles in many parts of the world. However, there have been relatively few efforts in quantifying the emission factors (EFs) and for estimating the potential emission reduction benefits using emission control technologies for these vehicles. This study characterized the black carbon (BC) component of particulate matter and NOx, CO, and CO2 EFs of selected diesel-powered off-road mobile sources in Mexico under real-world operating conditions using on-board portable emissions measurements systems (PEMS). The vehicles sampled included two backhoes, one tractor, a crane, an excavator, two front loaders, two bulldozers, an air compressor, and a power generator used in the construction and agricultural activities. For a selected number of these vehicles the emissions were further characterized with wall-flow diesel particle filters (DPFs) and partial-flow DPFs (p-DPFs) installed. Fuel-based EFs presented less variability than time-based emission rates, particularly for the BC. Average baseline EFs in working conditions for BC, NOx, and CO ranged from 0.04 to 5.7, from 12.6 to 81.8, and from 7.9 to 285.7 g/kg-fuel, respectively, and a high dependency by operation mode and by vehicle type was observed. Measurement-base frequency distributions of EFs by operation mode are proposed as an alternative method for characterizing the variability of off-road vehicles emissions under real-world conditions. Mass-based reductions for black carbon EFs were substantially large (above 99%) when DPFs were installed and the vehicles were idling, and the reductions were moderate (in the 20-60% range) for p-DPFs in working operating conditions. The observed high variability in measured EFs also indicates the need for detailed vehicle operation data for accurately estimating emissions from off-road vehicles in emissions inventories. IMPLICATIONS: Measurements of off-road vehicles used in construction and agricultural activities in Mexico using on-board portable emissions measurements systems (PEMS) showed that these vehicles can be major sources of black carbon and NOX. Emission factors varied significantly under real-world operating conditions, suggesting the need for detailed vehicle operation data for accurately estimating emissions inventories. Tests conducted in a selected number of sampled vehicles indicated that diesel particle filters (DPFs) are an effective technology for control of diesel particulate emissions and can provide potentially large emissions reduction in Mexico if widely implemented.

Estudio preliminar sobre el comportamiento de Aedes albopictus de la region central de Venezuela a insecticidas químicos / Preliminary study on the behavior of Aedes albopictus from the central region of Venezuela to chemical insecticides

Aedes albopictus es un competente vector del virus chikungunya, zika y de la mayor parte de los virus de encefalitis equina, capaz de transmitir al menos 24 arbovirus, susceptible a la infeccion (vertical y horizontalmente) por los serotipos del virus dengue. El objetivo fue realizar un estudio preliminar sobre el comportamiento frente a insecticidas organosinteticos de Ae. albopictus de diferentes localidades de tres estados centrales del pais, durante el periodo 2012-2014. Se realizaron pruebas biologicas con botellas tratadas con insecticidas, segun el metodo del CDC e igualmente evaluacion bioquimica para identificar los mecanismos de detoxificacion enzimaticos in vitro y mecanismos de resistencia in vivo con el sinergista butoxido de piperonilo (PB). Todas las cepas evaluadas presentaron sensibilidad al DDT (200 µg/mL) y cuatro de ellas a lambdacialotrina (6,25 µg/mL), solo una, Santos Michelena (SM) presento valores de sobrevivencia. Tambien esto fue observado con: malation (100 µg/mL) con una mortalidad en 30 minutos de 42,6% para Carabobo; 46,2% Distrito Capital (DC); 69,6% Zamora y 75,5% Mario Briceno Iragorry (MBI), solo resulto sensible SM. En cuanto a fenitrotion se encontraron valores de sobrevivencia con mortalidades en 30 minutos de 72,2%; para Carabobo, 30,7% DC y 45,8% MBI; solo expresaron sensibilidad Zamora y SM. En las cepas Carabobo y DC se observo el efecto sinergico FS = 3 y FS = 1,3, respectivamente. Se presume que los valores de sobrevivencia encontrados para insecticidas organofosforados pudiera asociarse con el incremento de esterasas alfa (a) y beta (b), en menor medida por la acetilcolinesterasa insensible (AChei) y las oxidasas con la sobrevivencia a lambdacialotrina en la cepa SM, lo cual podria comprobarse en estudios futuros a realizarse sobre resistencia a insecticidas. Los resultados encontrados en el presente trabajo, constituyen la base para su inicio a corto plazo en Ae. albopictus de Venezuela y la region, a fin de contribuir en la eficacia de las medidas de control quimico de esta especie de importancia medica.

Aedes albopictus is a competent vector of chikungunya virus, zika and most of the equine virus, capable of transmitting at least 24 arboviruses, susceptible to infection (vertically and horizontally) by serotypes of the dengue virus encephalitis. The objective was to conduct a preliminary study on the behavior against Ae. albopictus organosintetic insecticides from different locations in three central states of the country during the period 2012-2014. Bioassays with insecticide-treated bottles were performed according to the method of the CDC and also biochemical evaluation to identify the mechanisms of detoxification enzyme in vitro and in vivo mechanisms of resistance to the synergist piperonyl butoxide (PB). All strains tested showed sensitivity to DDT (200 µg/mL) and four of them lambdacyhalothrin (6.25 µg/mL), only one, Santos Michelena (SM) presented values of survival. This was also observed: malathion (100 µg/mL) with a mortality time (30 min) of 42.6% for Carabobo; 46.2% Capital District (DC); Zamora 69.6% and 75.5% Mario Briceno Iragorry (MBI) was sensitive only SM. As fenitrothion survival values encountered in the mortalities time (30 min) 72.2%; for Carabobo, 30.7% and 45.8% MBI DC; only expressed sensitivity Zamora and SM. In DC strains Carabobo and the synergistic effect was observed FS = 3 and FS = 1.3, respectively.It is presumed that the survival values found for organophosphate insecticides may be associated with increased esterase alpha (a) and beta (b), to a lesser extent insensitive acetylcholinesterase (ACHEI) and oxidases with survival to lambdacialotrine in strain SM , which could be verified in future studies to be carried out on insecticides resistance. The results found in the present work, constitute the basis for its short-term start in Ae. albopictus from Venezuela and the region, in order to contribute to the effectiveness of chemical control measures of this species of medical importance.

Traffic-related air pollution exposures and changes in heart rate variability in Mexico City: a panel study.

BACKGROUND: While air pollution exposures have been linked to cardiovascular outcomes, the contribution from acute gas and particle traffic-related pollutants remains unclear. Using a panel study design with repeated measures, we examined associations between personal exposures to traffic-related air pollutants in Mexico City and changes in heart rate variability (HRV) in a population of researchers aged 22 to 56 years. METHODS: Participants were monitored for approximately 9.5 hours for eight days while operating a mobile laboratory van designed to characterize traffic pollutants while driving in traffic and "chasing" diesel buses. We examined the association between HRV parameters (standard deviation of normal-to-normal intervals (SDNN), power in high frequency (HF) and low frequency (LF), and the LF/HF ratio) and the 5-minute maximum (or average in the case of PM(2.5)) and 30-, 60-, and 90-minute moving averages of air pollutants (PM(2.5), O(3), CO, CO(2), NO(2), NO(x), and formaldehyde) using single- and two-pollutant linear mixed-effects models. RESULTS: Short-term exposure to traffic-related emissions was associated with statistically significant acute changes in HRV. Gaseous pollutants - particularly ozone - were associated with reductions in time and frequency domain components (α = 0.05), while significant positive associations were observed between PM(2.5) and SDNN, HF, and LF. For ozone and formaldehyde, negative associations typically increased in magnitude and significance with increasing averaging periods. The associations for CO, CO(2), NO(2), and NO(x) were similar with statistically significant associations observed for SDNN, but not HF or LF. In contrast, PM(2.5) increased these HRV parameters. CONCLUSIONS: Results revealed an association between traffic-related PM exposures and acute changes in HRV in a middle-aged population when PM exposures were relatively low (14 µg/m(3)) and demonstrate heterogeneity in the effects of different pollutants, with declines in HRV - especially HF - with ozone and formaldehyde exposures, and increases in HRV with PM(2.5) exposure. Given that exposure to traffic-related emissions is associated with increased risk of cardiovascular morbidity and mortality, understanding the mechanisms by which traffic-related emissions can cause cardiovascular disease has significant public health relevance.

Estimating the health benefits from natural gas use in transport and heating in Santiago, Chile.

Chilean law requires the assessment of air pollution control strategies for their costs and benefits. Here we employ an online weather and chemical transport model, WRF-Chem, and a gridded population density map, LANDSCAN, to estimate changes in fine particle pollution exposure, health benefits, and economic valuation for two emission reduction strategies based on increasing the use of compressed natural gas (CNG) in Santiago, Chile. The first scenario, switching to a CNG public transportation system, would reduce urban PM2.5 emissions by 229 t/year. The second scenario would reduce wood burning emissions by 671 t/year, with unique hourly emission reductions distributed from daily heating demand. The CNG bus scenario reduces annual PM2.5 by 0.33 µg/m³ and up to 2 µg/m³ during winter months, while the residential heating scenario reduces annual PM2.5 by 2.07 µg/m³, with peaks exceeding 8 µg/m³ during strong air pollution episodes in winter months. These ambient pollution reductions lead to 36 avoided premature mortalities for the CNG bus scenario, and 229 for the CNG heating scenario. Both policies are shown to be cost-effective ways of reducing air pollution, as they target high-emitting area pollution sources and reduce concentrations over densely populated urban areas as well as less dense areas outside the city limits. Unlike the concentration rollback methods commonly used in public policy analyses, which assume homogeneous reductions across a whole city (including homogeneous population densities), and without accounting for the seasonality of certain emissions, this approach accounts for both seasonality and diurnal emission profiles for both the transportation and residential heating sectors.

The oxidative potential and biological effects induced by PM10 obtained in Mexico City and at a receptor site during the MILAGRO Campaign.

As part of a field campaign that studied the impact of Mexico City pollution plume at the local, sub-regional and regional levels, we studied transport-related changes in PM(10) composition, oxidative potential and in vitro toxicological patterns (hemolysis, DNA degradation). We collected PM(10) in Mexico City (T(0)) and at a suburban-receptor site (T(1)), pooled according to two observed ventilation patterns (T(0) → T(1) influence and non-influence). T(0) samples contained more Cu, Zn, and carbon whereas; T(1) samples contained more of Al, Si, P, S, and K (p < 0.05). Only SO(4)(-2) increased in T(1) during the influence periods. Oxidative potential correlated with Cu/Zn content (r = 0.74; p < 0.05) but not with biological effects. T(1) PM(10) induced greater hemolysis and T(0) PM(10) induced greater DNA degradation. Influence/non-influence did not affect oxidative potential nor biological effects. Results indicate that ventilation patterns had little effect on intrinsic PM(10) composition and toxicological potential, which suggests a significant involvement of local sources.

Formation of nanoparticles of blue haze enhanced by anthropogenic pollution.

The molecular processes leading to formation of nanoparticles of blue haze over forested areas are highly complex and not fully understood. We show that the interaction between biogenic organic acids and sulfuric acid enhances nucleation and initial growth of those nanoparticles. With one cis-pinonic acid and three to five sulfuric acid molecules in the critical nucleus, the hydrophobic organic acid part enhances the stability and growth on the hydrophilic sulfuric acid counterpart. Dimers or heterodimers of biogenic organic acids alone are unfavorable for new particle formation and growth because of their hydrophobicity. Condensation of low-volatility organic acids is hindered on nano-sized particles, whereas ammonia contributes negligibly to particle growth in the size range of 3-30 nm. The results suggest that initial growth from the critical nucleus to the detectable size of 2-3 nm most likely occurs by condensation of sulfuric acid and water, implying that anthropogenic sulfur emissions (mainly from power plants) strongly influence formation of terrestrial biogenic particles and exert larger direct and indirect climate forcing than previously recognized.

Characterization of aerosols containing Zn, Pb, and Cl from an industrial region of Mexico City.

Recent ice core measurements show lead concentrations increasing since 1970, suggesting new nonautomobile-related sources of Pb are becoming important worldwide (1). Developing a full understanding of the major sources of Pb and other metals is critical to controlling these emissions. During the March, 2006 MILAGRO campaign, single particle measurements in Mexico City revealed the frequent appearance of particles internally mixed with Zn, Pb, Cl, and P. Pb concentrations were as high as 1.14 microg/m3 in PM10 and 0.76 microg/m3 in PM2.5. Real time measurements were used to select time periods of interest to perform offline analysis to obtain detailed aerosol speciation. Many Zn-rich particles had needle-like structures and were found to be composed of ZnO and/or Zn(NO3)2 x 6H2O. The internally mixed Pb-Zn-Cl particles represented as much as 73% of the fine mode particles (by number) in the morning hours between 2-5 am. The Pb-Zn-Cl particles were primarily in the submicrometer size range and typically mixed with elemental carbon suggesting a combustion source. The unique single particle chemical associations measured in this study closely match signatures indicative of waste incineration. Our findings also show these industrial emissions play an important role in heterogeneous processing of NO(y) species. Primary emissions of metal and sodium chloride particles emitted by the same source underwent heterogeneous transformations into nitrate particles as soon as photochemical production of nitric acid began each day at approximately 7 am.

Assessment of diesel particulate matter exposure in the workplace: freight terminals.

A large study has been undertaken to assess the exposure to diesel exhaust within diesel trucking terminals. A critical component of this assessment is an analysis of the variation in carbonaceous particulate matter (PM) across trucking terminal locations; consistency in the primary sources can be effectively tracked by analyzing trends in elemental carbon (EC) and organic molecular marker concentrations. Ambient samples were collected at yard, dock and repair shop work stations in 7 terminals in the USA and 1 in Mexico. Concentrations of EC ranged from 0.2 to 12 microg m(-3) among the terminals, which corresponds to the range seen in the concentration of summed hopanes (0.5 to 20.5 ng m(-3)). However, when chemical mass balance (CMB) source apportionment results were presented as percent contribution to organic carbon (OC) concentrations, the contribution of mobile sources to OC are similar among the terminals in different cities. The average mobile source percent contribution to OC was 75.3 +/- 17.1% for truck repair shops, 65.4 +/- 20.4% for the docks and 38.4 +/- 9.5% for the terminal yard samples. A relatively consistent mobile source impact was present at all the terminals only when considering percentage of total OC concentrations, not in terms of absolute concentrations.

Traffic-related exposures, airway function, inflammation, and respiratory symptoms in children.

RATIONALE: Traffic-related emissions have been associated with respiratory symptoms in some studies. However, there is limited information on how traffic-related emissions relate to lung function and airway inflammation. OBJECTIVES: To determine the differential association of traffic-related exposures with exhaled nitric oxide (NO) and lung volumes and symptoms in children with and without asthma. METHODS: We performed a longitudinal study of 200 children from ages 6 to 12 years of whom half had physician-diagnosed asthma. Two-week NO(2) and 48-hour average levels of elemental carbon and particulate matter of less than 2.5 microm (PM(2.5)) were measured at participating schools. Road and traffic densities were determined at schools and at each participant's house. MEASUREMENTS AND MAIN RESULTS: In children with asthma, an interquartile increase in road density within the 50-, 100-, and 200-m home buffer areas was associated with increased exhaled NO (50 m: 28%; P = 0.03; 95% confidence interval [CI], 3-60; 100 m: 27%; P = 0.005; 95% CI, 8-49; 200 m: 17%, P = 0.09, 95% CI, -2 to 40), and reduced FEV(1) (50 m: -0.091 L; P = 0.038; 95% CI, -0.174 to -0.007; 100 m: -0.072 L, P = -0.028, 95% CI, -0.134 to -0.009; 200 m: -0.106 L, P = 0.002, 95% CI, -0.171 to -0.041]). Exposure to NO(2) at schools was marginally associated with reduced FEV(1) (-0.020; P = 0.060; 95% CI, -0.042 to 0.001). We did not observe significant associations with PM(2.5) or elemental carbon on exhaled NO. We did not observe significant reductions in lung volumes or changes in exhaled NO among healthy children. CONCLUSIONS: Vehicular traffic exposures are associated with increased levels of exhaled NO and reduced lung volumes in children with asthma.

Interaction of hydrogen chloride with ice surfaces: the effects of grain size, surface roughness, and surface disorder.

Characterization of the interaction of hydrogen chloride (HCl) with polar stratospheric cloud (PSC) ice particles is essential to understanding the processes responsible for ozone depletion. The interaction of HCl with ice was studied using a coated-wall flow tube with chemical ionization mass spectrometry (CIMS) between 5x10(-8) and 10(-4) Torr HCl and between 186 and 223 K, including conditions recently shown to induce quasi-liquid layer (QLL) formation on single crystalline ice samples. Measurements were performed on smooth and rough (vapor-deposited) polycrystalline ice films. A numerical model of the coated-wall flow reactor was used to interpret these results and results of studies on zone-refined ice cylinders with grain sizes on the order of several millimeters (reported elsewhere). We found that HCl adsorption on polycrystalline ice films typically used in laboratory studies under conditions not known to induce surface disordering consists of two modes: one relatively strong mode leading to irreversible adsorption, and one relatively weak binding mode leading to reversible adsorption. We have indirect experimental evidence that these two modes of adsorption correspond to adsorption to sites at crystal faces and those at grain boundaries, but there is not enough information to enable us to conclusively assign each adsorption mode to a type of site. Unlike what was observed in the zone-refined ice study, there was no strong qualitative contrast found between the HCl uptake curves under QLL versus non-QLL conditions for adsorption on smooth and vapor-deposited ices. We also found indirect evidence that HCl hexahydrate formation on ice between 3x10(-7) and 2x10(-6) Torr HCl and between 186 and 190 K is a process involving hydrate nucleation and propagation on the crystal surface, rather than one originating in grain boundaries, as has been suggested for ice formed at lower temperatures. These results underscore the dependence of the HCl-ice interaction on the characteristics of the ice substrate.

Platinum group elements in airborne particles in Mexico City.

Automobile exhaust catalysts using platinum group elements (PGE) have been mandatory on new cars in the Mexico City Metropolitan Area (MCMA) since 1991. Platinum, Pd, Rh, Ir, and Os concentrations and the isotopic composition of Os were determined in PM10 samples from the MCMA. Samples were prepared by isotope dilution NiS fire assay, and analysis was performed by magnetic sector ICP-MS using a single collector instrument for Pt, Pd, Rh, and Ir analysis and a multicollector instrument for Os analysis. Pt, Pd, and Rh concentrations at a downtown location (Merced) increased from < or =1.7 pg of Pt m(-3), 2.7 (4.0) pg of Pd m(-3), and 1.2+/-0.9 pg of Rh m(-3) in 1991 to 9.6 +/- 1.8 pg of Pt m(-3), 10.2+/-1.8 pg of Pd m(-3), and 2.8 +/-0.6 pg of Rh m(-3) in 2003. Concentrations at five sites in MCMA in 2003 averaged 9.3+/-1.9 pg of Pt m(-3), 11+/-4 pg of Pd m(-3), and 3.2+/- 1.0 pg of Rh m(-3). In contrast, Ir and Os concentrations and Os isotopic composition remained relatively constant and were 0.08+/-0.04 pg of Ir m(-3), 0.030 +/-0.007 pg of Os m(-3), and 0.60+/-0.04, respectively, in the MCMA in 2003. Elevated Pt, Pd, and Rh concentrations in the MCMA are attributed to automobile catalysts. A Pt-Pd-Rh concentration peak in 1993 suggests that early catalysts emitted a larger amount of PGE, possibly due to factors inherent in the technology or the use of inappropriate gasoline. Therefore, this study suggests that the current introduction of automobile catalysts in developing countries may result in elevated PGE concentrations if it is not accompanied by infrastructures and policy measures supporting their efficient use.

Modeling inorganic aerosols and their response to changes in precursor concentration in Mexico City.

Based on data from the 1997 Investigación sobre Materia Particulada y Deterioro Atmosférico-Aerosol and Visibility Evaluation Research (IMADA-EVER) campaign and the inorganic aerosol model ISORROPIA, the response of inorganic aerosols to changes in precursor concentrations was calculated. The aerosol behavior is dominated by the abundance of ammonia and thus, changes in ammonia concentration are expected to have a small effect on particle concentrations. Changes in sulfate and nitrate are expected to lead to proportional reductions in inorganic fine particulate matter (PM2.5). Comparing the predictions of ISORROPIA with the observations, the lowest bias and error are achieved when the aerosols are assumed to be in the efflorescence branch. Including crustal species reduces the bias and error for nitrate but does not improve overall model performance. The estimated response of inorganic PM2.5 to changes in precursor concentrations is affected by the inclusion of crustal species in some cases, although average responses are comparable with and without crustal species. Observed concentrations of particle chloride suggest that gas phase concentrations of hydrogen chloride may not be negligible, and future measurement campaigns should include observations to test this hypothesis. Our ability to model aerosol behavior in Mexico City and, thus, design control strategies, is constrained primarily by a lack of observations of gas phase precursors. Future campaigns should focus in particular on better understanding the temporal and spatial distribution of ammonia concentrations. In addition, gas phase observations of nitric acid are needed, and a measure of particle water content will allow stable versus metastable aerosol behavior to be distinguished.