NOx Exposure Research Articles

Self-reported traffic exposure is not strongly correlated modelled NOx in a Northern European cohort study

Introduction: Few studies have investigated the association between self-reported and modelled exposure to traffic pollutants, the objective of this study was to examine the correlation between modelled NOx and self-reported traffic exposure in 7 different northern European cities. Methods: Data from the third wave of the RHINE (Respiratory Health in Northern Europe, rhine.nu) cohort with seven study centres in Denmark, Estonia, Iceland, Norway and Sweden in 2011 was analysed. Vehicle exhaust (NOx) was modelled using dispersion models and LUR. Some rural areas were excluded as they fell outside model coverage. Self-reported exposure was measured by the questions; “Is your bedroom window near a street (less than 20 m)” with replies in four categories from “No” to “Yes, with very much traffic” and “Can you hear traffic noise from your bedroom?” with replies from “No” to “A lot”. Data were analysed using rank correlation of quartiles of modelled NOx in each centre. Results: Data on variables of interest were available for 50% to 99% of the 3rd wave cohort participants. The presence or size of a street near the bedroom window correlated significantly with modelled NOx in all centres. Hearing traffic noise at the bedroom window correlated with modelled NOx in most centres. However, all correlations were moderate. Conclusions: Self-reported residential proximity to traffic exhaust and traffic noise have low or moderate correlations with modelled vehicle exhaust concentration level at the home address.

The effect of population-scale human activity patterns on exposure to air pollution

Introduction. Exposure is often estimated only at the patient home address, inherently suggesting that subjects stay near their residence throughout the day. Methods. We studied exposure to nitrogen oxides of large groups of individuals by anonymously tracking their location during the day. Differences in exposure at the home address and while accounting for the time spend at work/school were studied. Geocoded residence and school addresses of 1.5 million schoolchildren age 6-18 and of the workplace of 400,000 adults were obtained from the Israeli Central Bureau of Statistics. Air pollution levels for 2008 were obtained using two models: a stationary nationwide land use regression model for NOx concentrations (250 m grid resolution), and a dynamic optimization dispersion model that provides half-hourly NO2 concentrations (500 m grid resolution) over smaller spatial extent but accounts for the spatiotemporally varying emissions and wind field. Results. (1) Due to daily varying NO2 concentrations, differences of 6-20 ppb were evident between the residence place and the workplace/school microenvironments. For example, in the Tel-Aviv metropolitan area about 50% of the adults and 66% of the children were exposed to higher concentrations at home than at work/school. (2) Using annual average NOx exposure estimates (to isolate the spatial commute contribution from the temporal daily variation contribution), about 58% of the adults and 70% of children experienced only small (<5 ppb) differences in exposure between the residence and work/school. (3) Commuters (defined as adults (children) that live more than 10 (5) km away from their residence place) and non-commuters had a similar distribution of differences in exposure to NOx between the two microenvironments. Conclusions. Reliable exposure estimation requires accurate information on (a) time-activity patterns (here in terms of spatiotemporal location), and (b) the pollutant spatiotemporal variation.

Contribution of coal-fired power plant emissions on respiratory symptom and disease prevalence

Introduction: This study investigates the association between exposure to ambient NOx and SO2 originating from power plant emissions and prevalence of obstructive pulmonary disease and related symptoms. The Orot Rabin coal-fired power plant is the largest power generating facility in the Eastern Mediterranean. Methods: Two novel methods assessing exposure to power plant-specific emissions were estimated for 2244 participants who completed the European Community Respiratory Health Survey. The “source approach” modeled emissions traced back to the power plant while the “event approach” identified peak exposures from power plant plume events. Three logistic regression models were assessed for each exposure metric and health outcome. The first model was adjusted for age and sex only. The second model added terms for potentially confounding covariates. The third model included a multi-pollutant analysis in which estimated exposure to SO2 was incorporated as a term in the analysis of NOx exposure, and vice-a-versa. Results: Respiratory symptoms, but not prevalence of asthma and COPD, were associated with estimates of power plant NOx emissions. The “source approach” yielded a better estimate of exposure to power plant emissions and showed a stronger dose–response relationship with outcomes. Conclusions: Calculating the portion of ambient pollution attributed to power plants emissions can be useful for air quality management purposes and targeted abatement programs.

Abstract 3436: Exposure to long-term traffic-related air pollutants, NO2 and NOX, and breast cancer incidence: The Multiethnic Cohort

Abstract Introduction: California has one of the highest levels of air pollution in the nation. Vehicle exhaust contains a mixture of gases and particulate matter that are known to have mutagenic and carcinogenic effects. Our objective was to examine the effects of markers of traffic-related air pollutants on breast cancer risk among the California component of Multiethnic Cohort (MEC). Methods: Residential addresses from baseline, 1993-1996, through 2010 for over 57,000 female California MEC participants were geocoded to latitude and longitude coordinates and used to estimate traffic-related air pollutant exposures of NO2 and NOX, using three complementary approaches: 1) land use regression (LUR) models based on passive diffusion measurements, land use patterns, roadway and traffic data, and satellite information (high spatial but low temporal resolution); 2) Bayesian kriging interpolation of state and national government air monitoring data (low spatial but high temporal resolution); 3) California line source dispersion model, version 4 (CALINE4) based on local traffic emissions, traffic volume, roadway geometry, meteorological conditions (high spatial and moderate temporal resolution). A total of 2,639 incident breast cancer cases (315 Japanese Americans, 830 Latinas, 974 African Americans and 511 whites) were identified by linkage to the California cancer registry. Cox proportional hazard regression was conducted to examine the long-term effects of NO2 and NOX (annual average exposure for up to 18 years), adjusting for age, race/ethnicity, education, health behaviors, established breast cancer risk factors, and neighborhood SES. Results: For NO2, per unit (ppb) increase in the interquartile range, a non-statistically significant association with breast cancer risk was observed with the LUR model among all women (OR = 1.04; 95% CI: 0.99-1.09). A significant positive association was seen in Japanese Americans (OR = 1.20; 95% CI: 1.07-1.34; p = 0.002) that met a conservative Bonferonni significance threshold (p = 0.003), but no associations were seen in African Americans, Latinas, and Whites. For NOx, per unit (ppb) increase in the interquartile range, no significant increased risk of breast cancer was seen with the CALINE4 model among all women, but a positive association was seen in Japanese Americans (OR = 1.10, 95% CI: 1.02-1.19; p = 0.016). NO2 and NOx exposures based on the kriging model were not associated with breast cancer risk among all women or in specific racial/ethnic groups. Conclusion: These preliminary findings suggest long-term NO2 and NOX exposure may influence breast cancer risk in Japanese Americans, using a LUR model of high spatial resolution and a CALINE4 model of high spatial and moderate temporal resolution. Future analyses will examine associations with other pollutants and differences in associations by neighborhood- and individual-level factors. Citation Format: Iona C. Cheng, Juan Yang, Chiuchen Tseng, Leo Lee, Jun Wu, Daniel Stram, Kristine Monroe, Loic Le Marchand, Scarlett Lin Gomez, Alice Whittemore, Salma Shariff-Marco, Beate Ritz, Anna Wu. Exposure to long-term traffic-related air pollutants, NO2 and NOX, and breast cancer incidence: The Multiethnic Cohort. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3436.

Exposure to Traffic-Related Air Pollution in Relation to Progression in Physical Disability among Older Adults.

Background:Physical disability is common though not inevitable in older age and has direct bearing on a person’s ability to perform activities essential for self-care and independent living. Air pollution appears to increase the risk of several chronic diseases that contribute to the progression of disability.Objective:We evaluated long-term exposure to traffic-related air pollution (TRAP) in relation to progression in physical disability.Methods:We conducted our investigation within the Chicago Health and Aging Project. We measured participants’ exposures to TRAP using two surrogates: residential proximity to major roads (1993 onwards) and ambient concentrations of oxides of nitrogen (NOX; 1999 onwards), predicted via a geographic information systems-based spatiotemporal smoothing model (cross-validation R2 = 0.87) that incorporated community-based monitoring and resolved intraurban exposure gradients at a spatial scale of tens of meters. Participants’ lower-extremity physical ability was assessed every 3 years (1993–2012) via tandem stand, chair stand, and timed walking speed.Results:In multivariable-adjusted analyses (n = 5,708), higher long-term NOX exposure was associated with significantly faster progression in disability. Compared with the 5-year decline in physical ability score among participants in the lowest quartile of NOX exposure, decline among those in the highest exposure quartile was 1.14 units greater (95% confidence interval [CI]: –1.86, –0.42), equivalent to 3 additional years of decline among those in the lowest exposure quartile. The association was linear across the continuum of NOX exposure: per 10-ppb increment in exposure, the 5-year decline in physical ability score was 0.87 unit greater (95% CI: –1.35, –0.39). Proximity to a major road was not associated with disability progression (n = 9,994).Conclusions:These data join a growing body of evidence suggesting that TRAP exposures may accelerate aging-related declines in health.Citation:Weuve J, Kaufman JD, Szpiro AA, Curl C, Puett RC, Beck T, Evans DA, Mendes de Leon CF. 2016. Exposure to traffic-related air pollution in relation to progression in physical disability among older adults. Environ Health Perspect 124:1000–1008; http://dx.doi.org/10.1289/ehp.1510089

Manipulating the gas–surface interaction between copper(II) oxide and mono-nitrogen oxides using temperature

In this contribution we investigate the effects of surface reactions of nitric oxide (NO) and nitrogen dioxide (NO2) on inkjet printed, p-type semiconducting copper(II) oxide (CuO) in different temperature regimes. For the first time we show that the gas-induced changes of the electrical conductivity of CuO upon NOx exposure may be tuned from oxidizing to reducing behavior and that the interaction may be effectively turned off. Using the experimental results of the transition from oxidizing to reducing characteristics we discuss the underlying surface reactions, which is of interest for metal-oxide based gas sensors for NOx in general. We demonstrate that the metal oxide reaction is solely governed by the temperature dependent chemical equilibrium of NO/NO2. Based on these results temperature modulation schemes to enhance the selectivity of metal-oxide gas sensors may be devised. We furthermore show that the CuO material system is able to detect low levels of NO/NO2, with a strongest oxidation response at 260°C and a strongest reduction response at 440°C for both oxides. Due to the high stability of the baseline resistivity of the layer, concentrations as low as 200ppb may be detected.

Associations Between Long-Term Exposure To Air Pollution And Perturbations In The Transcriptome

Epidemiologic studies have consistently shown associations between long-term exposure to ambient air pollution and chronic health effects such as cardiovascular disease, non-malignant respiratory disease, and lung cancer. We hypothesized that early indications of biological perturbations due to ambient air pollution could be detected in genome-wide gene expression profiles from peripheral blood mononuclear cells (PBMC) in healthy individuals. We assessed genome-wide gene expression in PBMC samples from study participants of two prospective cohorts from Italy (n=95) and Sweden (n=455). We estimated long-term air pollution (NOx) exposure levels for our study participants using exposure models developed within the European Study of Cohorts for Air Pollution Effects (ESCAPE). We used three complementary statistical approaches: univariate analysis (coupled with a 5% false discovery rate (FDR) control to account for multiple testing), elastic net regression, and Graphical Unit Evolutionary Stochastic Search (GUESS; a recent Bayesian variable selection approach), to identify for which genes expression level was altered by long-term exposure to NOx. There was little overlap between the distribution of NOx exposure levels in the Italian and the Swedish cohort (median; 5th-95th percentile: 94.2; 7.8-124.6 and 6.7; 4.8-19.5 μg/m3, respectively). We therefore conducted our primary analyses in the two cohorts separately. Using the univariate approach we identified one (unannotated) transcript in the Italian cohort and no transcripts in the Swedish cohort that were significantly associated at an FDR of 5%. While elastic net regression provided consistent results, GUESS provided less indication for an association with this probe in the Italian data. In summary, our study does not provide strong indications of transcriptomic changes related to air pollution within the exposure range studied.

Air Pollution And Other Risk Factors For Adverse Birth Outcomes And Infant Respiratory Health Findings From A South African Birth Cohort

Background. Oxides of nitrogen (NOx) have been associated with adverse birth outcomes (ABO) and with poor respiratory health among children. These exposure-related changes have not been previously described in HIV prevalent population. Aim. To determine associations between ABO and infant respiratory outcomes and exposures to NOx. in a population with additional socio-economic and infective risk factors. Methods. Pregnant women selected from public sector antenatal clinics in the highly industrialised south Durban (n=228) and less industrialised north Durban (n=174) were recruited in the first trimester, and followed through to delivery. Infants (n=189) of these mothers were followed up monthly, and clinically assessed at six months. Exposure was determined through land use regression models. Recruitment and follow-up is ongoing. Results. NOx varied between the south and north, with mean levels of 43.5 mg/m3 (range: 15.4–84.4 mg/m3) and 12.6 mg/m3 (7.7–21.7 mg/m3) respectively. Mean predicted exposures of the participants varied significantly geographically: south: 35.9 mg/m3 (range: 9.9-53.1 mg/m3); north: 22.4 mg/m3 (range: 2.5 – 42.1 mg/m3). Demographic profile was similar among those with varying exposure. The prevalence of ABO was 31.3%. There was no statistically increased exposure related risk for ABO, adjusted for ethnicity, education, income, HIV status and cigarette smoke. Intrauterine death (n=30) was strongly associated with HIV status (adjusted odds ratio = 11.8 (95% CI: 1.4 – 100.5)) and environmental tobacco smoke (OR=3.9; 95% CI: 1.3-12.9). Among the live births in the cohort, environmental, antenatal and adverse birth risk factors, were not associated with wheeze at six months. Conclusions. There is limited evidence for NOx exposure related adverse birth outcomes or infant wheeze within the cohort. Further exposure characterisation, as well as follow-up of infants is underway to ensure sufficient power to address the hypothesised relationships.

Potential health impacts of changes in air pollution exposure associated with moving traffic into a road tunnel.

A planned 21 km bypass (18 km within a tunnel) in Stockholm is expected to reduce ambient air exposure to traffic emissions, but same time tunnel users could be exposed to high concentrations of pollutants. For the health impacts calculations in 2030, the change in annual ambient NOX and PM10 exposure of the general population was modelled in 100 × 100 m(2) grids for Greater Stockholm area. The tunnel exposure was estimated based on calculated annual average NOX concentrations, time spent in tunnel and number of tunnel users. For the general population, we estimate annually 23.7 (95% CI: 17.7-32.3) fewer premature deaths as ambient concentrations are reduced. At the same time, tunnel users will be exposed to NOX levels up to 2000 μg/m(-3). Passing through the whole tunnel two times on working days would correspond to an additional annual NOX exposure of 9.6 μg/m(3). Assuming that there will be ~55,000 vehicles daily each way and 1.3 persons of 30-74 years of age in each vehicle, we estimate the tunnel exposure to result in 20.6 (95% CI: 14.1-25.6) premature deaths annually. If there were more persons per vehicle, or older and vulnerable people travelling, or tunnel dispersion conditions worsen, the adverse effect would become larger.

Maternal exposure to air pollution and type 1 diabetes – Accounting for genetic factors

BackgroundGenetic and non-genetic factors probably act together to initiate and accelerate development of type 1 diabetes [T1D]. One suggested risk factor contributing to development of T1D is air pollution. ObjectiveThe aim of the study was to investigate whether maternal exposure during pregnancy to air pollution, measured as nitrogen oxides [NOx] and ozone, in a low-dose exposure area was associated with the child developing T1D. MethodIn Scania (Skåne), the most southern county in Sweden, 84,039 infants were born during the period 1999–2005. By the end of April 2013, 324 of those children had been diagnosed with T1D. For each of those T1D children three control children were randomly selected and matched for HLA genotype and birth year. Individually modelled exposure data at residence during pregnancy were assessed for nitrogen oxides [NOx], traffic density and ozone. ResultsOzone as well as NOx exposures were associated with T1D. When the highest exposure group was compared to the lowest group an odds ratios of 1.62 (95% confidence interval [CI] 0.99–2.65) was observed for ozone in the second trimester and 1.58 (95% CI 1.06–2.35) for NOx in the third trimester. ConclusionThis study indicates that living in an area with elevated levels of air pollution during pregnancy may be a risk factor for offspring T1D.

Maternal Exposure to Air Pollution and the Risk for the Development of Type 1 Diabetes

Genetic and non-genetic factors act probably together to initiate and accelerate development of Type1 Diabetes [T1D]. One suggested risk factor contributing to development of T1D is air pollution. The aim of the study was to investigate if maternal exposure during pregnancy to air pollution, measured as nitrogen oxides [NOx], traffic density and ozone, in a low dose exposure area was associated with her child developing T1D. In Scania, the most southern county in Sweden, 84 039 infants were born during the period 1999-2005. By the end of April 2013, 324 of those children were diagnosed with T1D. For each of those T1D children three control children were randomly selected and matched for HLA genotype and birth year. Individually modelled exposure data at residence during pregnancy were assessed for nitrogen oxides [NOx], traffic density and ozone. Ozone as well as NOx exposures were associated with T1D. When the highest exposure quartile was compared to the lowest quartile an odds ratio of 1.70 (95% confidence interval [CI] 1.01 to 2.87) was observed for ozone in the second trimester and 1.57 (95% CI 1.06-2.34) for NOx in the third trimester. This study indicates that living in an area of elevated levels of air pollution during pregnancy may be a risk factor for T1D. The major strengths of this study is that we in a population-based prospective study have been able to, for the first time, analyze the association of air pollution during pregnancy and risk of childhood development of T1D after controlling for the genetic risk of disease.

Short-term exposure to high levels of air pollution as a risk factor for acute isolated pulmonary embolism

BackgroundThe association between air pollution exposure and occurrence of venous thromboembolism is a matter of debate. This retrospective case-control study investigated the associations between one month’s exposure to elevated levels of different pollutants (i.e. PM10, CO, NOx, O3, SO2, Benzene, Benzoapyrene, Nickel, Lead Arsenic) and the development of acute isolated pulmonary embolism (PE). MethodsThe cases included 33 patients consecutively admitted to Padua Hospital with an objectively proven diagnosis of acute unprovoked (i.e. without predisposing conditions) isolated (i.e. without deep vein thrombosis) PE. The control group consisted of 72 consecutive patients with objectively proven acute provoked (i.e. associated to predisposing conditions) isolated PE. Average mean concentrations of pollutants in the month before PE diagnosis were computed by monitors located at 2 different sites throughout the city of Padua, and were obtained from the Regional Agency for Environmental Protection. ResultsIndividuals who had PM10, NOx, Benzene, Benzoapyrene, Cadmium, and Lead exposure equal/above the 2nd tertile, measured in controls, showed a significant increase in the risk of unprovoked PE. In case of PM10 and Benzoapyrene this risk was not affected after adjustment for possible confounders. In fact, in the multivariate logistic regression analysis, the OR values were 5.24 (95% CI: 1.52-18.12) for PM10 and 3.95 (95% CI: 1.06-14.71) for Benzoapyrene exposure in the month before PE diagnosis. ConclusionsOur results, although preliminary, identify short-term (i.e. one month) exposure to elevate levels of air pollutants as a possible risk factor for the development of acute isolated PE. Larger studies are needed to confirm our results.

Land use regression models for estimating individual NOx and NO2 exposures in a metropolis with a high density of traffic roads and population

This study is conducted to characterize the intra-urban distribution of NOx and NO2; develop land use regression (LUR) models to assess outdoor NOx and NO2 concentrations, using the ESCAPE modeling approach with locally specific land use data; and compare NOx and NO2 exposures for children in the Taipei Metropolis by the LUR models, the nearest monitoring station, and kriging methods based on data collected at the measurement sites. NOx and NO2 were measured for 2weeks during 3 seasons at 40 sampling sites by Ogawa passive badges to represent their concentrations at urban backgrounds and streets from October 2009 to September 2010. Land use data and traffic-related information in different buffer zones were combined with measured concentrations to derive LUR models using supervised forward stepwise multiple regressions. The annual average concentrations of NOx and NO2 in Taipei were 72.4±22.5 and 48.9±12.2μg/m3, respectively, which were at the high end of all 36 European areas in the ESCAPE project. Spatial contrasts in Taipei were lower than those of the European areas in the ESCAPE project. The NOx LUR model included 6 land use variables, which were lengths of major roads within 25m, 25–50m, and 50–500m, urban green areas within 300m and 300–5000m, and semi-natural and forested areas within 500m, with R2=0.81. The NO2 LUR model included 4 land use variables, which were lengths of major roads within 25m, urban green areas within 100m, semi-natural and forested areas within 500m, and low-density residential area within 500m, with R2=0.74. The LUR models gave a wider variation in estimating NOx and NO2 exposures than either the ordinary kriging method or the nearest measurement site did for the children of Taiwan Birth Cohort Study (TBCS) in Taipei.

Long-term exposure to traffic-related air pollution and cardiac events in four cohorts from Stockholm

Long-term exposure to traffic-related air pollution and cardiac events in four cohorts from Stockholm Background. Effects of long-term exposure to air pollution on cardiovascular outcomes have been studied extensively, but there are few prospective studies with individually assessed exposure to air pollution in relation to development of non-fatal and fatal cardiac events (CE). Furthermore, the role of timing of exposure has not been adequately investigated. Aim. To assess the risk of CE in relation to long-term exposure to air pollution, with particular focus on the influence by timing of exposure. Methods. Four cohorts enrolled 1992-2004 in Stockholm County were followed until 2009. Individual exposure to NOX and PM10 from local traffic was assessed with dispersion models and applied to the residential addresses during follow-up. Information on life style and other environmental exposures were obtained from questionnaires and clinical tests. Information on CE morbidity and mortality was retrieved from national registries. Cox regression analyses were performed on each cohort and combined using a meta-analysis approach. Adjustment was made for individual and contextual confounders. Results. The analyses included 19939 participants contributing a total of 744 CEs, including 146 fatal, until end of follow-up. In the combined analysis there was a hazard ratio of 1.09 (95% CI: 0.81-1.38) for CE associated with an average of 7.1 µg/m3 difference in PM10 exposure (5th to 95th percentile). The corresponding hazard ratio for nonfatal CE was 1.16 (95% CI: 0.84-1.48). In general, the results for NOX were similar to those for PM10, and the two exposures were highly correlated. No heterogeneity was apparent in risk estimates between different cohorts and sensitivity analyses did not reveal clear differences in relation to age and sex. Conclusions. We observed consistent non-significant associations between PM10 or NOX exposure and the risk of nonfatal cardiac events. However, the statistical power was limited to detect small excess risks.

Trends in NOx exposure contrast from 1975 to 2004 in the Gothenburg Primary Prevention Study cohort

Trends in NOx exposure contrast from 1975 to 2004 in the Gothenburg Primary Prevention Study cohort

Dosimeter-Type NOx Sensing Properties of KMnO4 and Its Electrical Conductivity during Temperature Programmed Desorption

An impedimetric NOx dosimeter based on the NOx sorption material KMnO4 is proposed. In addition to its application as a low level NOx dosimeter, KMnO4 shows potential as a precious metal free lean NOx trap material (LNT) for NOx storage catalysts (NSC) enabling electrical in-situ diagnostics. With this dosimeter, low levels of NO and NO2 exposure can be detected electrically as instantaneous values at 380 °C by progressive NOx accumulation in the KMnO4 based sensitive layer. The linear NOx sensing characteristics are recovered periodically by heating to 650 °C or switching to rich atmospheres. Further insight into the NOx sorption-dependent conductivity of the KMnO4-based material is obtained by the novel eTPD method that combines electrical characterization with classical temperature programmed desorption (TPD). The NOx loading amount increases proportionally to the NOx exposure time at sorption temperature. The cumulated NOx exposure, as well as the corresponding NOx loading state, can be detected linearly by electrical means in two modes: (1) time-continuously during the sorption interval including NOx concentration information from the signal derivative or (2) during the short-term thermal NOx release.

Electrical conductivity study of NOx trap materials BaCO3 and K2CO3/La-Al2O3 during NOx exposure

Alkaline (earth-) carbonates are applied in NOx storage and reduction catalysts, given their ability to accumulate NO2 in excess oxygen environments, and releasing it under rich-burn conditions. The dependency of their conductivity on the NOx loading state makes them suitable as NO2 sensitive layers and enables the in situ characterization of the status of such catalyst systems. The conductivity of the NOx trap components BaCO3 and K2CO3, with different morphologies, is analyzed in various NOx containing atmospheres by impedance spectroscopy. While the stepwise uptake of NO2 can be detected electrically on both carbonates, only a weak corresponding influence of NO is detected. The increase in the conductivity of the carbonates during NO2 accumulation can be described as a diffusion controlled process with a characteristic nucleation delay in the case of BaCO3. Arrhenius-like plots comparing the conductivities of the carbonates in the unloaded and NO2 saturated states from 250 to 600°C reveal that the conductivity of BaCO3 is more sensitive to NO2 than those of K2CO3/La-Al2O3, but the latter exhibiting about five orders of magnitude higher conductivity.

A comparison of population air pollution exposure estimation techniques with personal exposure estimates in a pregnant cohort

There is increasing evidence of the harmful effects for mother and fetus of maternal exposure to air pollutants. Most studies use large retrospective birth outcome datasets and make a best estimate of personal exposure (PE) during pregnancy periods. We compared estimates of personal NOx and NO2 exposure of pregnant women in the North West of England with exposure estimates derived using different modelling techniques. A cohort of 85 pregnant women was recruited from Manchester and Blackpool. Participants completed a time-activity log and questionnaire at 13-22 weeks gestation and were provided with personal Ogawa samplers to measure their NOx/NO2 exposure. PE was compared to monthly averages, the nearest stationary monitor to the participants' home, weighted average of the closest monitor to home and work location, proximity to major roads, as well as to background modelled concentrations (DEFRA), inverse distance weighting (IDW), ordinary kriging (OK), and a land use regression model with and without temporal adjustment. PE was most strongly correlated with monthly adjusted DEFRA (NO2r = 0.61, NOxr = 0.60), OK and IDW (NO2r = 0.60; NOxr = 0.62) concentrations. Correlations were stronger in Blackpool than in Manchester. Where there is evidence for high temporal variability in exposure, methods of exposure estimation which focus solely on spatial methods should be adjusted temporally, with an improvement in estimation expected to be better with increased temporal variability.

The electrical properties of NOx-storing carbonates during NOx exposure

In order to gain a deeper understanding of the different components in multi-component automotive catalyst systems and integrating type NOx-sensors, in-situ electrical methods are examined. The conductivity of BaCO3 and K2CO3, key components in automotive NOx storage catalysts, was examined as a function of gas composition and temperature. Impedance measurements performed on BaCO3, K2CO3, and equimolar mixtures of both, demonstrated that, in all cases, the resistance decreases in the presence of NO2 gas with progressive NOx sorption on the carbonate surface. Mixing the hygroscopic but low resistivity K2CO3 with the very highly resistive but stable BaCO3 resulted in greater stability than K2CO3 alone, as well as improved ability to measure resistivity changes. The resistance of the mixture recovered about 50% of its value after removing NO2 from the gas stream, believed to result from migration of sorbed NOx from K to Ba, instead of desorption alone. These results on NOx trap materials show that in-situ impedance spectroscopy measurements offer real-time characterization of NOx loading levels in lean NOx trap catalyst components.

Selectivity, stability and repeatability of In2O3 thin films towards NOx at high temperatures (≥500 °C)

Solid state sensors need to be selective to the target gas and stable in their performance in the sensing environment. We have investigated the selectivity, stability, and repeatability of indium oxide (In2O3) thin film sensor to detect NOx (25ppm) in presence of other exhaust gas pollutants including H2, NH3 and CO2 at high operating temperatures (≥400°C) in N2 carrier gas. When exposed individually to 25ppm NOx, 100ppm NH3, 5000ppm H2 and 1000ppm CO2, the sensor is selective to NOx with higher sensor response (S∼23) to NOx species compared to other gases (S∼1). The sensor response (S) drastically decreases when either NH3 or H2 are added to the NOx test gas. In2O3 samples without promoter layers exhibited higher sensor response to NOx in presence of 100ppm NH3 when compared to Au promoter samples. Fourier transform infrared spectroscopy (FT-IR) was employed in order to investigate the gas-phase reactions between NOx and NH3 or H2 at high temperatures (>400°C). At >500°C, NH3 and H2 reduce NOx to H2O and N2 which may explain the drastic reduction in NOx response at high temperatures (>500°C). Exposure to H2 also etched the In2O3 film which comprises the stability when the sensor is operated in a H2 rich environment (>2500ppm H2). In2O3 thin films deposited in an oxygen environment (25% O2) which presented the highest and quickest response were repeatable to 25ppm NOx exposures with overall variation in sensor response <10%.