Ppb NO2 Research Articles

Low-level NO gas sensing properties of $$\hbox {Zn}_{1-x}\hbox {Sn}_{x}\hbox {O}$$ Zn 1 - x Sn x O nanostructure sensors under UV light irradiation at room temperature

\(\hbox {Zn}_{1-x}\hbox {Sn}_{x}\hbox {O}\) (\(x=0\), 0.05, 0.10, 0.15, 0.20) nanostructures have been grown through the successive ionic layer adsorption and reaction method. The structural, morphological and compositional properties of the nanostructures have been characterized through X-ray diffraction, scanning electron microscope and energy dispersive X-ray analysis, respectively. The NO gas sensing properties of sensors to 20 ppb have been systematically investigated in the dark and under UV light irradiation. A \(\hbox {Zn}_{0.90}\hbox {Sn}_{0.10}\hbox {O}\) sensor has exhibited the highest response for 20 ppb NO gas compared with other sensors. The sensor response has increased from 1.9 to 43% depending on the UV light irradiation for the \(\hbox {Zn}_{0.90}\hbox {Sn}_{0.10}\hbox {O}\) sensor. \(\hbox {Zn}_{0.90}\hbox {Sn}_{0.10}\hbox {O}\) nanostructure can be used as a suitable gas sensor material for detection of low concentration levels of NO gas.

Study on highly selective sensing behavior of ppb-level oxidizing gas sensors based on Zn2SnO4 nanoparticles immobilized on reduced graphene oxide under humidity conditions

Highly selective oxidizing gas sensors are of great importance for environmental pollution monitoring. In this work, a hybrid material containing Zn2SnO4 nanoparticles (NPs) and immobilized reduced graphene oxide (Zn2SnO4-RGO) was developed as a high performance gas sensing material for the detection of ppb-levels of oxidizing gases (NO2 and O3). The structural, morphological and compositional properties of the Zn2SnO4-RGO hybrids were systematically characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), which demonstrated the successful anchoring of Zn2SnO4 NPs on RGO nanosheets. The obtained Zn2SnO4-RGO hybrids exhibited outstanding sensing performance for detecting oxidizing gases (NO2 and O3) with very low cross sensitivities to reducing gases, such as C2H5OH, CH3COCH3 and CO. The Zn2SnO4-RGO based sensors exhibited high response values of up to 3.50 for 500 ppb NO2, which is higher than that for detection of 500 ppb O3 (1.78) at 30 °C under 50% relative humidity (RH). Moreover, the NO2 sensing performances of Zn2SnO4-RGO-based sensors were investigated under various RH. In all cases, the sensors based on RGO and Zn2SnO4-RGO hybrids presented p-type behavior. The sensors based on Zn2SnO4-RGO hybrids also exhibited high response values of up to 3.62 for 1 ppm NO2 at 50 °C in 80% RH, which is much higher than that of pure RGO (1.31). The excellent sensing performances are mainly ascribed to the synergetic effect of Zn2SnO4 NPs and RGO. Furthermore, the surface reaction between Zn2SnO4-RGO hybrids and NO2 can be concluded from Operando diffuse reflectance infrared Fourier transformed spectroscopy (Operando DRIFT).

Highly sensitive NO2 sensors based on core‐shell array of silicon nanowires/polypyrrole and new insight into gas sensing mechanism of organic/inorganic hetero‐contact

Uniform core‐shell hetero‐array of polypyrrole‐wrapped silicon nanowires (LNWs/PPy C‐S nanowires) with enhanced gas‐sensing response at room temperature was prepared via a two‐step process. The aligned silicon nanowires were first formed by metal‐assisted chemical etching (MACE). To achieve a loose silicon nanowires (LNWs) array facilitating the uniform deposition of PPy shell on whole wire surface, a repeated MACE treatment was further developed based on reoxidation of the MACE‐produced Ag dendrites. The PPy‐shell with adjustable thickness was then formed uniformly on the LNWs via vapor chemical polymerization (VCP) of pyrrole monomer (Py). The gas sensor based on the well‐defined LNWs/PPy C‐S heteronanowires array exhibits about 8.2 times response enhancement to 5 ppm NO2 gas compared with the pristine one at room temperature. Very low detection resolution of 50 ppb NO2 is observed when PPy shell has thickness of about 10 nm. The organic/inorganic C‐S composite of LNWs/PPy nanowires shows a different characteristic of shell thickness effect on sensing response from the general semiconductor oxides‐based C‐S sensor; much thinner PPy shell is extremely preferred for higher sensing response. A sensing mechanism model was proposed to demonstrate the featured effect of organic shell thickness on sensing behavior of LNWs/PPy C‐S heteronanowires. POLYM. COMPOS., 40:3275–3284, 2019. © 2019 Society of Plastics Engineers

In situ investigation of NOᵪ photocatalytic degradation: Case study in an open space office in Manchester, UK

Indoor air is contaminated by numerous pollutants, which impact human health, comfort and productivity. These pollutants have various indoor sources such as building materials, furniture, combustion appliances or tobacco smoke. However, the pollution also comes from outside. In urban area, nitrogen oxides (NOx) emitted into the atmosphere can reach alarming levels. These traffic-related pollutants, which seriously impact the global environment and human health, can infiltrate inside buildings. Therefore, limiting the amount of breathable NOx in outdoor and indoor environments is an important priority for the modern society. The photocatalytic process has attracted particular attention in the last two decades and has proved to be efficient to reduce the concentration of NOx. However, further work has to be conducted to assess its efficiency in real indoor environments. The purpose of this paper was to report on the indoor air quality in an open space office in Manchester, UK. Focus was made on nitric oxide (NO) and nitrogen dioxide (NO2). The indoor concentrations of both gases were monitored from 14 January 2019 to 7 April 2019. During this period, a photocatalytic coating was applied to a part of the indoor wall. The influence of this coating on the level of NOx was assessed by comparing the indoor concentrations before and after the application. An attention was paid to the correlation between outdoor and indoor pollution and to the effect of other parameters such as temperature, humidity, pressure and O3 concentration. The results showed that the photocatalytic process led to a decrease in the NOx concentration. The likelihood to find concentrations above 35 ppb for NO and 7.5 ppb for NO2 was clearly reduced after the coating application.

Photo-enhanced gas sensing of SnS2 with nanoscale defects.

Recently a SnS2 based NO2 gas sensor with a 30 ppb detection limit was demonstrated but this required high operation temperatures. Concurrently, SnS2 grown by chemical vapor deposition is known to naturally contain nanoscale defects, which could be exploited. Here, we significantly enhance the performance of a NO2 gas sensor based on SnS2 with nanoscale defects by photon illumination, and a detection limit of 2.5 ppb is achieved at room temperature. Using a classical Langmuir model and density functional theory simulations, we show S vacancies work as additional adsorption sites with fast adsorption times, higher adsorption energies, and an order of magnitude higher resistance change compared with pristine SnS2. More interestingly, when electron–hole pairs are excited by photon illumination, the average adsorption time first increases and then decreases with NO2 concentration, while the average desorption time always decreases with NO2 concentration. Our results give a deep understanding of photo-enhanced gas sensing of SnS2 with nanoscale defects, and thus open an interesting window for the design of high performance gas sensing devices based on 2D materials.

Sub-ppm level NO2 sensing properties of polyethyleneimine-mediated WO3 nanoparticles synthesized by a one-pot hydrothermal method

A novel sensing material of polyethyleneimine-mediated WO3 nanoparticles was prepared by a simple and efficient one-pot hydrothermal method. The structure and morphology characteristics of the as-prepared WO3 nanoparticles were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The results showed that the as-prepared WO3 nanomaterials were composed of highly dispersible WO3 nanoparticles, and these nanoparticles with the particle size in the range of 10–50 nm showed a monoclinic structure. NO2 sensing measurements demonstrated that WO3 nanoparticles-based gas sensor exhibited superior response, outstanding selectivity, excellent reversibility, and good long-term stability. The sensor response increased as NO2 concentration increased. The highest response value of 251.7 was achieved to 5 ppm NO2 at the optimal operating temperature of 100 °C. Especially, the sensor response could reach 3.2–50 ppb NO2. It also exhibited fast response and recovery times with a high sensor response even in a high-humidity environment. The excellent gas sensing properties of WO3 nanoparticles could be ascribed to their high effective surface areas as well as numerous oxygen vacancies, which foresee the great potential application for fast and effective detection of sub-ppm level NO2 under different humidity environments.

Sensing properties of amperometric ppb-level NO2 sensor based on sodium ion conductor with sensing electrodes comprising different WO3 nanostructures

In this study, amperometric NO2 sensors based on Na+ superionic conductor electrolyte and sensing electrodes with different WO3 nanostructures (WO3 nanoparticles, WO3 nanosheets, and mesoporous WO3) have been fabricated and compared. Sensing properties, such as optimum test temperature, sensitivity, repeatability, and selectivity have been determined and compared. Compared with the literatures, the sensors, prepared using three different WO3 nanostructures, all showed improved sensing properties to 100–1000 ppb NO2 at low work temperatures of 100–150 °C. Among above sensors, the sensor equipped with mesoporous WO3 sensing electrode exhibited the best amperometric sensitivity characteristics and the minimum test temperature. The relationship between the sensing properties and the mesoporous structure has also been discussed. What’s more, the sensor can test ppb-level NO2 in low temperature, which makes it possible to monitor low concentrations of NO2 in the air.

Enhanced humidity resistance of porous SiNWs via OTS functionalization for rarefied NO2 detection

Porous silicon nanowires (SiNWs) is considered as one of promising candidates for high-performance NO2 sensor application in human health and quality life owing to its fast response and stable operation at room temperature. However, the development of SiNWs-based gas sensors for stable detection of ppb-level NO2 in practical high-humidity environments remains a challenge. In this study, octadecyltrichlorosilane (OTS) was utilized to modify partially insensitive SiNWs surface with the Si-O bond, yielding an immunity to high humidity in gas detection process. The modified OTS provides an umbrella-like barrier blocking water molecules attraction on the nanowire surface which disinhibits the main adsorption sites and sensing channels of the sensor. The OTS-modified porous SiNWs (OTS/SiNWs) sensor exhibited a practical capability to detect 5 ppb NO2 at humidity of 25%–55% RH and a response of 1.8% to 50 ppb NO2 at 75% RH at room temperature. Moreover, the fast response/recovery characteristics and good reversibility of the OTS/SiNWs sensor was observed even under high humidity conditions. In addition, the OTS/SiNWs sensor displayed excellent stability to humidity variations. The enhanced gas sensing performance is attributed to a marriage of porous structure of SiNWs and OTS. The simple modification for SiNWs-based gas sensor will broaden new avenues, not only in chemical trace detection, but also in high humidity health monitoring.

The enhanced NO2 sensing properties of SnO2 nanoparticles/reduced graphene oxide composite

Multiple techniques were utilized to characterize the structure and morphology of the SnO2/reduced graphene oxide (rGO) composite, in which the composite was prepared by a facile one-pot microwave-assisted hydrothermal method. As a result, SnO2 nanoparticles with diameters of 3–5 nm were anchored uniformly on both sides of the rGO sheets. Meanwhile, a series of resistive-type gas sensors based on SnO2/rGO composite and pure SnO2 were fabricated and tested for analyzing the effects on introducing rGO. The results revealed that, the composite exhibited obviously enhanced gas sensing properties towards NO2 with high response, fast response and recovery speed, and good selectivity and reproducibility. At 75 °C, the response of the composite to 350 ppb NO2 was about 6.6 times of that to pure SnO2. In addition, the response and recovery time of the sensor was greatly reduced from 39.2/54.7 to 6.5/1 min, and the detecting limit of the sensor was even as low as 50 ppb. Provided with the enlarged surface area and local p-n heterojunctions, the synergistic effect of SnO2 nanoparticles and rGO contributed to the enhanced gas sensing properties of SnO2/rGO composite.

Sol gel graphene/TiO2 nanoparticles for the photocatalytic-assisted sensing and abatement of NO2

Human exposure to volatile organic compounds and NO2 can lead to health problems, therefore strategies to mitigate against the risks are required. Abatement and sensing are approaches which could both neutralise and monitor these species thus providing a safer environment and warning occupants of harmful levels. This paper presents pure TiO2 and TiO2/graphene hybrids synthesized through a sol-gel route. Electron optical, helium ion microscopy, X-ray diffraction and spectroscopic methods have been applied to elucidate the physical and chemical behaviour. NO2 sensing properties of TiO2/graphene hybrids formed by the addition of graphene to the reaction vessel prior to initiating the sol gel reaction followed by annealing (GTiO2S), and an alternative manufacturing method involving the addition of graphene to TiO2 nanoparticles which had already been annealed (GTiO2M) were compared and evaluated. A conductometric sensor based on TiO2/graphene prepared using material GTiO2S showed a higher response to NO2 compared to sensors based on pure TiO2 and TiO2/graphene prepared with material GTiO2M. Under UV irradiation generated by a low power LED, the sensor showed a remarkably enhanced response to 1750 ppb NO2, about double the response in the dark, and a limit of detection of about 50 ppb of NO2 (Signal/Noise = 3). Photocatalytic tests to assess the degradation of NOx showed that TiO2/graphene hybrids using material GTiO2S were the most active amongst the whole series of TiO2-based materials. Our data highlights the unique characteristics of material GTiO2S TiO2/graphene and the suitability for multi-purpose applications in the field of environmental monitoring and remediation. The capability of the material for both sensing and abatement of NOx could be exploited to offer a safer environment through providing a warning of the presence of NOx whilst also reducing levels.

Design and implementation of a preconcentrator with Zeolite NaY for sensitivity enhancement of commercial gas sensors at low NO2 concentrations

Zeolite NaY was used to implement a NO2 preconcentrating system for the first time which provided the detection of ppb concentration levels of NO2 with high response level. NO2 gas is among air pollutants that significantly affect the quality of human health, even at low concentrations, which necessitates commercial NO2 sensors to attain low detection capability. In this work, we have reported responses of a commercial NO2 sensor to low concentration levels of NO2. Responses were improved by ∼44 times through using a designed and fabricated preconcentration system. The preconcentrator was composed of different sections in which the most important part was zeolite NaY as a NO2 adsorbent: it adsorbed NO2 molecules from the air polluted with 300 ppb NO2 during the adsorption cycle, then by applying a heating pulse, it was forced to release preadsorbed NO2 species into a smaller chamber in which a commercial gas sensor was placed to monitor the variations of NO2. In this process, the sensor response increased noticeably. System features such as durability and cross sensitivity, and preconcentrator working conditions, such as desorption temperature, duration of adsorption time, heating rate, and the air circulation flow were investigated. Results were described and it is shown that NO2 detection at ppb levels with high sensitivity is possible with such a low price preconcentration system.

Measurements of NO and NO<sub>2</sub> exchange between the atmosphere and <i>Quercus agrifolia</i>

Abstract. NO2 foliar deposition through the stomata of leaves has been identified as a significant sink of NOx within a forest canopy. In this study, we investigated NO2 and NO exchange between the atmosphere and the leaves of the native California oak tree Quercus agrifolia using a branch enclosure system. NO2 detection was performed with laser-induced fluorescence (LIF), which excludes biases from other reactive nitrogen compounds and has a low detection limit of 5–50 ppt. We performed both light and dark experiments with concentrations between 0.5 and 10 ppb NO2 and NO under constant ambient conditions. Deposition velocities for NO2 during light and dark experiments were 0.123±0.009 and 0.015±0.001 cm s−1, respectively. Much slower deposition was seen for NO, with deposition velocities of 0.012±0.002 and 0.005±0.002 cm s−1 measured during light and dark experiments, respectively. This corresponded to a summed resistance of the stomata and mesophyll of 6.9±0.9 s cm−1 for NO2 and 140±40 s cm−1 for NO. No significant compensation point was detected for NO2 uptake, but compensation points ranging from 0.74 to 3.8 ppb were observed for NO. NO2 and NO deposition velocities reported here are comparable both with previous leaf-level chamber studies and inferences from canopy-level field measurements. In parallel with these laboratory experiments, we have constructed a detailed 1-D atmospheric model to assess the contribution of leaf-level NOx deposition to the total NOx loss and NOx canopy fluxes. Using the leaf uptake rates measured in the laboratory, these modeling studies suggest that loss of NOx to deposition in a California oak woodland competes with the pathways of HNO3 and RONO2 formation, with deposition making up 3 %–22 % of the total NOx loss. Additionally, foliar uptake of NOx at these rates could account for ∼15 %–30 % canopy reduction of soil NOx emissions.

Facile preparation of Silicon/ZnO thin film heterostructures and ultrasensitive toxic gas sensing at room temperature: Substrate dependence on specificity

Two types of silicon-Zinc oxide (ZnO) heterostructures were prepared simply by depositing (drop casting) chemically prepared ZnO nanoparticles onto single crystalline (p-type) silicon substrates (Si) as well as electrochemically prepared p-type porous silicon (PS). ZnO nanoparticles and PS/ZnO structures were characterized structurally by various techniques. By depositing in-plane gold contacts on the heterostructures, gas sensors were fabricated and characterized electrochemically by dc and ac impedance measurements. The PS/ZnO sensors showed specific response at room temperature for NO2 with increase in current and no significant response for other reducing and oxidizing gases. The sensor is sensitive to 200 ppb NO2 at 25 °C with 35% change in current and 50 s response time. Temperature dependent studies of sensor in the range of 25–100 °C have shown maximum sensitivity at 40 °C (50% change for 200 ppb) with decreasing sensitivity thereafter (23% change at 60 °C), indicating the suitability of the sensor till 60 °C. Alternatively Si/ZnO heterostructures showed maximum response with NO2, along with lesser specific responses for SO2 and NH3. Detailed multifrequency impedance studies with temperature suggested the role of space charge layers at various interfaces in the charge transport properties of PS/ZnO and Si/ZnO heterostructures resulting in their specific gas sensing properties.

Effects of ambient humidity and temperature on the NO2 sensing characteristics of WS2/graphene aerogel

The effects of ambient humidity and temperature on the NO2 sensing characteristics of WS2/graphene aerogel (WS2/GA) composite are investigated. In order to probe the gas sensing performances of WS2/GA, the sensor is fabricated by integrating WS2/GA with a microfabricated two-electrode device. The WS2/GA is characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and nitrogen porosimetry. This hybrid nanomaterial is found to improve the selectivity to NO2, compared to control graphene and WS2 aerogels. The NO2 sensing performance of the WS2/GA-based sensors is investigated under different relative humidities (0–60%), and ambient temperatures (room temperature (RT) to 180 °C). In all cases, the sensors exhibit p-type behavior. In dry atmosphere, faster response and better recovery are obtained with increasing temperature, reaching optimum sensing performance around 180 °C. At room temperature, interestingly, humidity is found helpful for enhancing the response and recovery of the sensor to NO2. Detection limits in the range of 10–15 ppb NO2 were determined. A possible gas sensing mechanism for this composite aerogel is proposed.

Long-term exposure to air pollution and the risk of suicide death: A population-based cohort study

Suicide is a major public health problem. Previous studies have reported a significant association between acute exposure to air pollution and suicide; little attention has been paid to the long-term effects of air pollution on risk of suicide. We investigated whether long-term exposure to particulate matter of ≤10μm in diameter (PM10), nitrogen dioxide (NO2), and sulfur dioxide (SO2) would be associated with a greater risk of death by suicide. The study sample comprised 265,749 adults enrolled in the National Health Insurance Service-National Sample Cohort (2002−2013) in South Korea. Suicide death was defined as per ICD-10 code. Data on air pollution exposure used nationwide monitoring data, and individual exposure levels were assigned using geographic information systems. Air pollution exposure was categorized as the interquartile range (IQR) and quartiles. Hazards ratios (HRs) were calculated for the occurrence of suicide death after adjusting for potential covariates. During the study period, 564 (0.2%) subjects died from suicide. Increases in IQR pollutants (7.5μg/m3 for PM10, 11.8ppb for NO2, and 0.8ppb for SO2) significantly increased HR for suicide death [PM10: HR=3.09 (95% CI: 2.63–3.63); NO2: HR=1.33 (95% CI: 1.09–1.64); and SO2: HR=1.15 (95% CI: 1.07–1.24)]. Compared with the lowest level of air pollutants (Quartile 1), the risk of suicide significantly increased in the highest quartile level (Quartile 4) for PM10 (HR=4.03; 95% CI: 2.97–5.47) and SO2 (HR=1.65; 95% CI: 1.29–2.11) and in the third quartile for NO2 (HR=1.52; 95% CI: 1.17–1.96). HRs for subjects with a physical or mental disorder were higher than that those for subjects without the disorder. Subjects living in metropolitan areas were more vulnerable to long-term PM10 exposure than those living in non-metropolitan areas. Long-term exposure to air pollution was associated with a significantly increased risk of suicide death. People having underlying diseases or living in metropolitan areas may be more susceptible to high air pollution exposure.

Pd loading induced excellent NO2 gas sensing of 3DOM In2O3 at room temperature

Pd loaded three dimensionally ordered macroporous (3DOM) In2O3 sensors were fabricated by reduction precipitation method with a uniform distribution of Pd nanoparticles (NPs). The response of 0.5 wt% Pd loaded 3DOM In2O3 is 980 for 500 ppb NO2 which is over 5 times higher than that of pure In2O3 at room temperature. Our work presents a relatively simple but more efficient approach for NO2 detection without extra heating. Pd inducing surface-modification effectively modulates the thickness of electron depletion layer, which is the dominant sensing mechanism for enhancing NO2 performance. When Pd NPs are loaded on the surface of 3DOM In2O3 support, not only the amount of surface deficiency and carrier concentration increase, but also electrons flow further from In2O3 to Pd NPs. All of these results in the formation of Pd-In2O3 Schottky contact and eventually widen the depletion layer on the In2O3 support. Apparently, our work presents a relatively simple but more efficient approach for NO2 detection without extra heating, indicating that Pd loaded 3DOM In2O3 sensors would be more suitable for future applications.

Highly sensitive NO2 gas sensor of ppb-level detection based on In2O3 nanobricks at low temperature

The brick-like In2O3 nanomaterials were synthesized by oil bath precipitation and subsequent calcination method without any templates or surfactants. Technologies of X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were carried out to characterize the morphological and structural of the In2O3 samples. Photoluminescence spectra (PL) and X-ray photoelectron spectroscopy (XPS) were used to illustrate the influence of material surface states and internal defects on gas-sensing properties. The In2O3 nanomaterials annealed at 400 °C exhibited a high response (402) toward 500 ppb NO2 with the fast response/recovery time (114 s/49 s) at rather low operating temperature of 50 °C. Besides, it had a good linear relationship in the range of 100–500 ppb. Such excellent gas sensing properties could be on account of the relative large surface area, abundant adsorbed oxygen and good electrical properties.

Evaluation of an Air Quality Health Index for Predicting the Mutagenicity of Simulated Atmospheres.

No study has evaluated the mutagenicity of atmospheres with a calculated air quality health index (AQHI). Thus, we generated in a UV-light-containing reaction chamber two simulated atmospheres (SAs) with similar AQHIs but different proportions of criteria pollutants and evaluated them for mutagenicity in three Salmonella strains at the air-agar interface. We continuously injected into the chamber gasoline, nitric oxide, and ammonium sulfate, as well as either α-pinene to produce SA-PM, which had a high concentration of particulate matter (PM): 119 ppb ozone (O3), 321 ppb NO2, and 1007 μg/m3 PM2.5; or isoprene to produce SA-O3, which had a high ozone (O3) concentration: 415 ppb O3, 633 ppb NO2, and 55 μg/m3 PM2.5. Neither PM2.5 extracts, NO2, or O3 alone, nor nonphoto-oxidized mixtures were mutagenic or cytotoxic. Both photo-oxidized atmospheres were largely direct-acting base-substitution mutagens with similar mutagenic potencies in TA100 and TA104. The mutagenic potencies [(revertants/h)/(mgC/m3)] of SA-PM (4.3 ± 0.4) and SA-O3 (9.5 ± 1.3) in TA100 were significantly different ( P < 0.0001), but the mutation spectra were not ( P = 0.16), being ∼54% C → T and ∼46% C → A. Thus, the AQHI may have some predictive value for the mutagenicity of the gas phase of air.

Associations between Prenatal Exposure to Air Pollutants and Developing Autism: A Population-Based Cohort Study in Metro Vancouver, Canada

Background/Aim: This study assesses the association between PM2.5, NO, and NO2 exposures with autism spectrum disorder (ASD) incidence in a large population-based cohort. ASD is a neurodevelopmental condition characterized by impaired social communication and repetitive or stereotypic behaviours. The aetiology of ASD is poorly defined, but prior studies suggest an association between air pollution exposure and ASD. Methods: We conducted a retrospective cohort study to evaluate prenatal exposure to PM2.5, NO, and NO2 and the development of ASD among all live birthsin Metro Vancouver, Canada, from2004–2009. Children were identified with ASD by the BC AutismAssessment Network, using standardized assessment of Autism Diagnostic Interview-Revised and Autism Diagnostic Observation Schedule (ADOS). We developed temporally adjusted land use regression models to estimate monthly mean exposures to ambient pollution at the home residence for each woman throughout the pregnancy. We used logistic regression to estimate odds ratios (OR) and 95% confidence intervals (CI) of exposure for the entire pregnancy, adjusting for maternal age and birthplace, parity, multiple births, co-parent status, income bands, and child sex. Results: The cohort comprised 132,257 births, of which 1,307 (1%) children were diagnosed with ASD. The mean PM2.5exposure during pregnancy was 3.5 μg/m3 (IQR = 1.5 μg/m3); the mean NO was 20.8 ppb (IQR = 10.7 ppb); and mean NO2 was 15.2 ppb (IQR = 4.7 ppb). The adjusted OR for ASD per 10 μg/m3 of PM2.5 during pregnancy was 1.29 (95% CI: 0.92–1.79); per 10 ppb of NO, 1.05 (95% CI: 1.00–1.10); and per 10 ppb or NO2, 1.11 (95% CI:0.99–1.25). Conclusions: Using individual, specific diagnostic clinical data, we observed some evidence of associations between exposure to air pollutants and increased ASD risk in a population-based cohort with relatively low levels of air pollution.

Photochemical Conversion of Surrogate Emissions for Use in Toxicological Studies: Role of Particulate- and Gas-Phase Products.

The production of photochemical atmospheres under controlled conditions in an irradiation chamber permits the manipulation of parameters that influence the resulting air-pollutant chemistry and potential biological effects. To date, no studies have examined how contrasting atmospheres with a similar Air Quality Health Index (AQHI), but with differing ratios of criteria air pollutants, might differentially affect health end points. Here, we produced two atmospheres with similar AQHIs based on the final concentrations of ozone, nitrogen dioxide, and particulate matter (PM2.5). One simulated atmosphere (SA-PM) generated from irradiation of ∼23 ppmC gasoline, 5 ppmC α-pinene, 529 ppb NO, and 3 μg m-3 (NH4)2SO4 as a seed resulted in an average of 976 μg m-3 PM2.5, 326 ppb NO2, and 141 ppb O3 (AQHI 97.7). The other atmosphere (SA-O3) generated from 8 ppmC gasoline, 5 ppmC isoprene, 874 ppb NO, and 2 μg m-3 (NH4)2SO4 resulted in an average of 55 μg m-3 PM2.5, 643 ppb NO2, and 430 ppb O3 (AQHI of 99.8). Chemical speciation by gas chromatography showed that photo-oxidation degraded the organic precursors and promoted the de novo formation of secondary reaction products such as formaldehyde and acrolein. Further work in accompanying papers describe toxicological outcomes from the two distinct photochemical atmospheres.