Public health impacts of secondary particulate formation from aromatic hydrocarbons in gasoline

Secondary organic aerosol formation from monocyclic aromatic hydrocarbons: insights from laboratory studies

Monocyclic aromatic hydrocarbons (MAHs) are key anthropogenic pollutants and often dominate the volatile organic compound emissions and secondary organic aerosol (SOA) formation especially in the urban atmosphere. To evaluate the environmental impacts of SOA formed from the oxidation of MAHs (aromatic SOA), it is of great importance to elucidate their chemical composition, formation mechanism, and physicochemical properties under various atmospheric conditions. Here we seek to compile a common framework for the current studies on aromatic SOA formation and summarize the knowledge on what has been primarily learned from laboratory studies. This review begins with a brief summary of MAHs' emission characteristics, followed by an overview of atmospheric degradation mechanisms for MAHs as well as gas- and particle-phase reactions involving aromatic SOA formation. SOA formation processes highlighted in this review are complex and depend highly on environmental conditions, posing a substantial challenge for theoretical description of aromatic SOA formation. Therefore, the following issues are further discussed in detail: the response of gas-phase chemistry and aromatic SOA mass yield as well as composition to NO_x levels, particle-phase reactions and molecular characterization of aromatic SOA in the presence of acidic sulfate, and physicochemical processes of SOA formation involving gas- or particle-phase water. Building on this current understanding, available experimental studies on the effects of environmental conditions were explored. A brief description of the atmospheric importance of aromatic SOA including their optical properties and health influences is also presented. Finally, we highlight the current challenges in laboratory studies and outline directions for future aromatic SOA research.

Estimating Occupational Exposure to VOCs, SVOCs, Particles and Participant Survey Reported Symptoms in Central Thailand Rice Farmers Using Multiple Sampling Techniques

Thailand is known for its agricultural productivity and rice exportation. Most farms use small machines and manual labor, creating potential exposure to multiple health hazards. A cross-sectional study was conducted to measure pollutants liberated during preparation, pesticide application, and harvesting. Thirty rice farmers, mostly males from 41 to 50 years old, participated. The participant survey data showed that 53.3% of the respondents spent >2 h per crop on preparation, <1 h on pesticide application, and about 1-2 h harvesting; 86.7% of the respondents maintained and stored mechanical applicators at home, suggesting possible after-work exposures. Gloves, fabric masks, boots, and hats were worn during all activities, and >90% wore long sleeved shirts and pants. VOCs and SVOCs were collected using charcoal tubes and solid phase micro sample extraction (SPME). An analysis of the charcoal and SPME samplers found that 30 compounds were detected overall and that 10 were in both the charcoal tubes and SPME samplers. The chemicals most often detected were 1, 1, 1 Trichloro ethane and xylene. Additionally, farmers experienced the highest exposure to particulates during harvesting. These results demonstrated that farmers experience multiple exposures while farming and that risk communication with education or training programs may mitigate exposure.

Exposure characterization and estimation of benchmark dose for cancer biomarkers in an occupational cohort of diesel engine testers

Exposure to diesel engine exhaust (DEE) was associated with various adverse health effects including lung cancer. Particle size distribution and profiles of organic compounds in both particle and gas phases of DEE that could provide valuable insights into related health effects were measured in a diesel engine testing workshop. Concentrations of urinary 6 mono-hydroxylated polycyclic aromatic hydrocarbons (OH-PAHs) in 137 DEE-exposed workers and 127 non-DEE-exposed workers were determined. Benchmark dose method was applied to estimate lower limit of benchmark dose (BMDL) of urinary OH-PAHs most specific to DEE exposure for previously reported cancer biomarkers. We found that 84.3% of diesel exhaust particles were ultrafine particles. Indeno[123-cd]pyrene and phenanthrene were the most abundant carcinogenic and noncarcinogenic PAHs in the particle phase of DEE, respectively. Principal component analysis demonstrated that urinary hydroxyphenanthrene (OHPhe) had highest loading value on principal component (PC) representative of DEE exposure and lowest loading value on PC representative of smoking status. BMDLs of urinary OHPhe from best-fitting models for cancer biomarkers including micronucleus and 1,N⁶-ethenodeoxyadenosine were 1.08 μg/g creatinine and 2.82 μg/g creatinine, respectively. These results provided basis for understanding DEE exposure induced health effects and potential threshold for regulating DEE levels in an occupational setting.

Dynamic Oxidative Potential of Atmospheric Organic Aerosol under Ambient Sunlight

The atmospheric process dynamically changes the chemical compositions of organic aerosol (OA), thereby complicating the interpretation of its health effects. In this study, the dynamic evolution of the oxidative potential of various OA was studied, including wood combustion particles and secondary organic aerosols (SOA) generated from different hydrocarbons (i.e., gasoline, toluene, isoprene, and α-pinene). The oxidative potential of OA at different aging stages was subsequently measured by the dithiothreitol consumption (DTT_m, mass normalized). We hypothesized that DTT consumptions by OA were modulated by catalytic particulate oxidizers (e.g., quinones), noncatalytic particulate oxidizers (e.g., organic hydroperoxides and peroxyacyl nitrates) and electron-deficient alkenes. The results of this study showed that the oxidative potential of OA decreased after an extended period of aging due to the decomposition of particulate oxidizers and electron-deficient alkenes. Quinones (GC-MS data) partially attributed to the DTT_m of fresh wood smoke particles but rapidly dropped with aging. In biogenic SOA, organic hydroperoxides (4-nitrophenyl boronic acid assay) exclusively accounted for DTT_m and decreased with aging. The DTT_m of aromatic SOA, mainly comprising organic hydroperoxides and electron-deficient alkenes (FTIR data), was shortly elevated during the early atmospheric process; however, it showed a noticeable decrease (32-75%) for a long period of aging. We concluded that fresh or moderately aged OA are more reactive to a sulfhydryl group than highly aged OA.

Improving organic aerosol treatments in CESM/CAM5: Development, application, and evaluation

New treatments for organic aerosol (OA) formation have been added to a modified version of the CESM/CAM5 model (CESM-NCSU). These treatments include a volatility basis set treatment for the simulation of primary and secondary organic aerosols (SOAs), a simplified treatment for organic aerosol (OA) formation from glyoxal, and a parameterization representing the impact of new particle formation (NPF) of organic gases and sulfuric acid. With the inclusion of these new treatments, the concentration of oxygenated organic aerosol increases by 0.33 µg m-3 and that of primary organic aerosol (POA) decreases by 0.22 µg m-3 on global average. The decrease in POA leads to a reduction in the OA direct effect, while the increased OOA increases the OA indirect effects. Simulations with the new OA treatments show considerable improvement in simulated SOA, oxygenated organic aerosol (OOA), organic carbon (OC), total carbon (TC), and total organic aerosol (TOA), but degradation in the performance of HOA. In simulations of the current climate period, despite some deviations from observations, CESM-NCSU with the new OA treatments significantly improves the magnitude, spatial pattern, seasonal pattern of OC and TC, as well as, the speciation of TOA between POA and OOA. Sensitivity analysis reveals that the inclusion of the organic NPF treatment impacts the OA indirect effects by enhancing cloud properties. The simulated OA level and its impact on the climate system are most sensitive to choices in the enthalpy of vaporization and wet deposition of SVOCs, indicating that accurate representations of these parameters are critical for accurate OA-climate simulations.

Emission characteristics of volatile organic compounds and their secondary organic aerosol formation potentials from a petroleum refinery in Pearl River Delta, China

A campaign was carried out to measure the emission characteristics of volatile organic compounds (VOCs) in different areas of a petroleum refinery in the Pearl River Delta (PRD) region in China. In the refining area, 2-methylpentane, 2,3-dimethylbutane, methylcyclopentane, 3-methylhexane, and butane accounted for >50% of the total VOCs; in the chemical industry area, 2-methylpentane, p-diethylbenzene, 2,3-dimethylbutane, m-diethylbenzene and 1,2,4-trimethylbenzene were the top five VOCs detected; and in the wastewater treatment area, the five most abundant species were 2-methylpentane, 2,3-dimethylbutane, methylcyclopentane, 3-methylpentane and p-diethylbenzene. The secondary organic aerosol (SOA) formation potential was estimated using the fractional aerosol coefficients (FAC), secondary organic aerosol potential (SOAP), and SOA yield methods. The FAC method suggests that toluene, p-diethylbenzene, and p-diethylbenzene are the largest contributors to the SOA formation in the refining, chemical industry, and wastewater treatment areas, respectively. With the SOAP method, it is estimated that toluene is the largest contributor to the SOA formation in the refining area, but o-ethyltoluene contributes the most both in the chemical industry and wastewater treatment areas. For the SOA yield method, aromatics dominate the yields and account for nearly 100% of the total in the three areas. The SOA concentrations estimated of the refining, chemical industry and wastewater treatment areas are 30, 3835 and 137μgm^-3, respectively. Despite the uncertainties and limitations associated with the three methods, the SOA yield method is suggested to be used for the estimation of SOA formation from the petroleum refinery. The results of this study have demonstrated that the control of VOCs, especially aromatics such as toluene, ethyltoluene, benzene and diethylbenzene, should be a focus of future regulatory measures in order to reduce PM pollution in the PRD region.

Evaluating the Effects of Aromatics Content in Gasoline on Gaseous and Particulate Matter Emissions from SI-PFI and SIDI Vehicles

We assessed the emissions response of a fleet of seven light-duty gasoline vehicles for gasoline fuel aromatic content while operating over the LA92 driving cycle. The test fleet consisted of model year 2012 vehicles equipped with spark-ignition (SI) and either port fuel injection (PFI) or direct injection (DI) technology. Three gasoline fuels were blended to meet a range of total aromatics targets (15%, 25%, and 35% by volume) while holding other fuel properties relatively constant within specified ranges, and a fourth fuel was formulated to meet a 35% by volume total aromatics target but with a higher octane number. Our results showed statistically significant increases in carbon monoxide, nonmethane hydrocarbon, particulate matter (PM) mass, particle number, and black carbon emissions with increasing aromatics content for all seven vehicles tested. Only one vehicle showed a statistically significant increase in total hydrocarbon emissions. The monoaromatic hydrocarbon species that were evaluated showed increases with increasing aromatic content in the fuel. Changes in fuel composition had no statistically significant effect on the emissions of nitrogen oxides (NOx), formaldehyde, or acetaldehyde. A good correlation was also found between the PM index and PM mass and number emissions for all vehicle/fuel combinations with the total aromatics group being a significant contributor to the total PM index followed by naphthalenes and indenes.

Oxidative potential and inflammatory impacts of source apportioned ambient air pollution in Beijing

Air pollution exposure is associated with a range of adverse health impacts. Knowledge of the chemical components and sources of air pollution most responsible for these health effects could lead to an improved understanding of the mechanisms of such effects and more targeted risk reduction strategies. We measured daily ambient fine particulate matter (<2.5 μm in aerodynamic diameter; PM2.5) for 2 months in peri-urban and central Beijing, and assessed the contribution of its chemical components to the oxidative potential of ambient air pollution using the dithiothreitol (DTT) assay. The composition data were applied to a multivariate source apportionment model to determine the PM contributions of six sources or factors: a zinc factor, an aluminum factor, a lead point factor, a secondary source (e.g., SO4(2-), NO3(2-)), an iron source, and a soil dust source. Finally, we assessed the relationship between reactive oxygen species (ROS) activity-related PM sources and inflammatory responses in human bronchial epithelial cells. In peri-urban Beijing, the soil dust source accounted for the largest fraction (47%) of measured ROS variability. In central Beijing, a secondary source explained the greatest fraction (29%) of measured ROS variability. The ROS activities of PM collected in central Beijing were exponentially associated with in vivo inflammatory responses in epithelial cells (R2=0.65-0.89). We also observed a high correlation between three ROS-related PM sources (a lead point factor, a zinc factor, and a secondary source) and expression of an inflammatory marker (r=0.45-0.80). Our results suggest large differences in the contribution of different PM sources to ROS variability at the central versus peri-urban study sites in Beijing and that secondary sources may play an important role in PM2.5-related oxidative potential and inflammatory health impacts.

Effects of diesel engine exhaust origin secondary organic aerosols on novel object recognition ability and maternal behavior in BALB/c mice

Epidemiological studies have reported an increased risk of cardiopulmonary and lung cancer mortality associated with increasing exposure to air pollution. Ambient particulate matter consists of primary particles emitted directly from diesel engine vehicles and secondary organic aerosols (SOAs) are formed by oxidative reaction of the ultrafine particle components of diesel exhaust (DE) in the atmosphere. However, little is known about the relationship between exposure to SOA and central nervous system functions. Recently, we have reported that an acute single intranasal instillation of SOA may induce inflammatory response in lung, but not in brain of adult mice. To clarify the whole body exposure effects of SOA on central nervous system functions, we first created inhalation chambers for diesel exhaust origin secondary organic aerosols (DE-SOAs) produced by oxidation of diesel exhaust particles caused by adding ozone. Male BALB/c mice were exposed to clean air (control), DE and DE-SOA in inhalation chambers for one or three months (5 h/day, 5 days/week) and were examined for memory function using a novel object recognition test and for memory function-related gene expressions in the hippocampus by real-time RT-PCR. Moreover, female mice exposed to DE-SOA for one month were mated and maternal behaviors and the related gene expressions in the hypothalamus examined. Novel object recognition ability and N-methyl-D-aspartate (NMDA) receptor expression in the hippocampus were affected in male mice exposed to DE-SOA. Furthermore, a tendency to decrease maternal performance and significantly decreased expression levels of estrogen receptor (ER)-α, and oxytocin receptor were found in DE-SOA exposed dams compared with the control. This is the first study of this type and our results suggest that the constituents of DE-SOA may be associated with memory function and maternal performance based on the impaired gene expressions in the hippocampus and hypothalamus, respectively.

Inhalation of air polluted with gasoline vapours alters the levels of amino acid neurotransmitters in the cerebral cortex, hippocampus, and hypothalamus of the rat

BACKGROUND

This study was designed to investigate the impact of exposure to the vapours of two kinds of gasoline, a widely used fuel for the internal combustion engines on the levels of the amino acid neurotransmitters of the rat brain. Recent studies provide strong evidence for a causative role for traffic-related air pollution on morbidity outcomes as well as premature death (Health Effects Institute, 2009; Levy et al., 2010; von Stackelberg et al., 2013). Exposure to the vapours of gasoline or its constituents may be accidental, occupational by workers at fuel stations and factories, or through abuse as a mean of mood alteration (Fortenberry, 1985; Mc Garvey et al., 1999). Two kinds of gasoline that are common in Egypt have been used in this study. The first contains octane enhancers in the form of lead derivatives (leaded gasoline; G1) and the other contains methyl-tertiary butyl ether (MTBE) as the octane enhancer (unleaded gasoline; G2). The levels of the major excitatory (aspartic acid and glutamic acid) and the inhibitory (GABA and glycine) amino acid neurotransmitters were determined in the cerebral cortex, hippocampus, and hypothalamus.

RESULTS

The current study revealed that the acute inhalation of air polluted with the two types of gasoline vapours (1/2 LC50 for 30 min) induced elevation in the levels of aspartic and glutamic acids along with a decrease in glycine and GABA in most studied brain areas. Chronic inhalation of both types of gasoline (a single daily 30-min session of 1/5 LC50 for 60 days) caused a significant increase in the aspartic and glutamic acid concentrations of the hippocampus without affecting the levels of GABA or glycine.

CONCLUSION

Acute and chronic inhalation of either one of G1 and G2 vapours induced a disturbance and fluctuation in the levels of the free amino acids that act as excitatory and inhibitory neurotransmitters in the brain areas under investigation. These neurotransmitters are fundamental for the communicative functioning of the neurons and such effects may have a profound impact on the cognitive and sensorimotor functions of the brain resulting in serious psychological and physiological disorders..