Nucleation, Transformation, and Impacts of Atmospheric Aerosols

Atmospheric aerosols are a key contributor to pollution, adversely affect human health, and can alter global climate. Several questions concerning atmospheric aerosols persist, including: ‘Which atmospheric species are integral for aerosol formation in the atmosphere?’, ‘What happens to aerosols after emission into or formation in the atmosphere?’, ‘Does maternal exposure to aerosols during pregnancy fundamentally alter her offspring?’, and ‘Can we utilize gas phase chemistry models to further our understanding of atmospheric aerosols?’. A series of chamber, observational, and computational studies have been conducted to investigate these scientific questions. Globally, new particle formation (NPF) events account for more than 50% of the aerosols in the troposphere, but the chemical species and mechanisms responsible for NPF have yet to be fully understood. To explicate the role of organic compounds in NPF, laboratory experiments have been conducted to investigate aerosol nucleation and growth from the photochemical oxidation of biogenic and anthropogenic volatile organic compounds (VOCs). Here we show that the NPF is dependent on the VOC species and that the global pattern of NPF is likely governed by the available VOCs. A suite of instruments was deployed in Beijing to measure a comprehensive set of aerosol properties in order to elucidate the aerosol formation mechanisms and the evolution of aerosol properties. NPF consistently occurred on clean, windy days, and the high aerosol mass observed during haze events is attributable to the continuous growth from the nucleation-mode particles over multiple days to produce a high concentration of larger particles. Our results reveal that the severe haze in Beijing is likely due to the concentrated aerosol precursor gases and the large-scale meteorological conditions. Model simulations indicate that the persistent high concentrations of NO2 in Beijing and the frequent periods of high aerosol loading leads to elevated HONO levels and sustained oxidizing capacity. To determine the mechanism through which aerosols influence human health, a series of animal exposure studies have been conducted to investigate the transgenerational effects. In each experiment, Sprague-Dawley rats were continuously exposed between days 0 and 18 of gestation to controlled conditions to represent either clean (~5 µg m^-3) or polluted (~150 µg m^-3) environments. The gestation length, litter size, birth weight, and sex ratio were assessed throughout the animal exposure studies. The preliminary results indicate the development of several organs and the birth weight may be influenced by prenatal exposure to pollutants and the degree of response may also be sex dependent

Markedly enhanced absorption and direct radiative forcing of black carbon under polluted urban environments

Black carbon (BC) exerts profound impacts on air quality and climate because of its high absorption cross-section over a broad range of electromagnetic spectra, but the current results on absorption enhancement of BC particles during atmospheric aging remain conflicting. Here, we quantified the aging and variation in the optical properties of BC particles under ambient conditions in Beijing, China, and Houston, United States, using a novel environmental chamber approach. BC aging exhibits two distinct stages, i.e., initial transformation from a fractal to spherical morphology with little absorption variation and subsequent growth of fully compact particles with a large absorption enhancement. The timescales to achieve complete morphology modification and an absorption amplification factor of 2.4 for BC particles are estimated to be 2.3 h and 4.6 h, respectively, in Beijing, compared with 9 h and 18 h, respectively, in Houston. Our findings indicate that BC under polluted urban environments could play an essential role in pollution development and contribute importantly to large positive radiative forcing. The variation in direct radiative forcing is dependent on the rate and timescale of BC aging, with a clear distinction between urban cities in developed and developing countries, i.e., a higher climatic impact in more polluted environments. We suggest that mediation in BC emissions achieves a cobenefit in simultaneously controlling air pollution and protecting climate, especially for developing countries

Persistent sulfate formation from London Fog to Chinese haze

Sulfate aerosols exert profound impacts on human and ecosystem health, weather, and climate, but their formation mechanism remains uncertain. Atmospheric models consistently underpredict sulfate levels under diverse environmental conditions. From atmospheric measurements in two Chinese megacities and complementary laboratory experiments, we show that the aqueous oxidation of SO2 by NO2 is key to efficient sulfate formation but is only feasible under two atmospheric conditions: on fine aerosols with high relative humidity and NH3 neutralization or under cloud conditions. Under polluted environments, this SO2 oxidation process leads to large sulfate production rates and promotes formation of nitrate and organic matter on aqueous particles, exacerbating severe haze development. Effective haze mitigation is achievable by intervening in the sulfate formation process with enforced NH3 and NO2 control measures. In addition to explaining the polluted episodes currently occurring in China and during the 1952 London Fog, this sulfate production mechanism is widespread, and our results suggest a way to tackle this growing problem in China and much of the developing world

Benzene Exposure and Cancer Risk from Commercial Gasoline Station Fueling Events Using a Novel Self-Sampling Protocol

Tens of millions of individuals go to gasoline stations on a daily basis in the United States. One of the constituents of gasoline is benzene, a Group 1 carcinogen that has been strongly linked to both occupational and non-occupational leukemias. While benzene content in gasoline is federally regulated, there is approximately a thirty-year data gap in United States research on benzene exposures from pumping gasoline. Using a novel self-sampling protocol with whole air canisters, we conducted a gasoline pumping exposure assessment for benzene, toluene, ethylbenzene, and xylene (BTEX) on Baltimore, MD consumers. Geometric mean exposures (geometric standard deviations) were 3.2 (2.7) ppb,9.5 (3.5) ppb, 2.0 (2.8) ppb, and 7.3 (3.0) ppb, respectively, on 32 samples. Using the benzene exposures, we conducted consumer and occupational probabilistic risk assessments and contextualized the risk with ambient benzene exposure risk. We found that the consumer scenarios did not approach the 1:1,000,000 excess risk management threshold and that the occupational scenario did not exceed the 1:10,000 excess risk management threshold. Further, in all Monte Carlo trials, the ambient risk from benzene exposure exceeded that of pumping risk for consumers, but that in approximately 30% of occupational trials, the pumping risk exceeded the ambient risk

Laboratory Chamber Evaluation of Flow Air Quality Sensor PM2.5 and PM10 Measurements

The emergence of low-cost air quality sensors as viable tools for the monitoring of air quality at population and individual levels necessitates the evaluation of these instruments. The Flow air quality tracker, a product of Plume Labs, is one such sensor. To evaluate these sensors, we assessed 34 of them in a controlled laboratory setting by exposing them to PM10 and PM2.5 and compared the response with Plantower A003 measurements. The overall coefficient of determination (R2) of measured PM2.5 was 0.76 and of PM10 it was 0.73, but the Flows’ accuracy improved after each introduction of incense. Overall, these findings suggest that the Flow can be a useful air quality monitoring tool in air pollution areas with higher concentrations, when incorporated into other monitoring frameworks and when used in aggregate. The broader environmental implications of this work are that it is possible for individuals and groups to monitor their individual exposure to particulate matter pollution

Stationary and portable multipollutant monitors for high-spatiotemporal-resolution air quality studies including online calibration

The distribution and dynamics of atmospheric pollutants are spatiotemporally heterogeneous due to variability in emissions, transport, chemistry, and deposition. To understand these processes at high spatiotemporal resolution and their implications for air quality and personal exposure, we present custom, low-cost air quality monitors that measure concentrations of contaminants relevant to human health and climate, including gases (e.g., O3, NO, NO2, CO, CO2, CH4, and SO2) and size-resolved (0.3–10 μm) particulate matter. The devices transmit sensor data and location via cellular communications and are capable of providing concentration data down to second-level temporal resolution. We produce two models: one designed for stationary (or mobile platform) operation and a wearable, portable model for directly measuring personal exposure in the breathing zone. To address persistent problems with sensor drift and environmental sensitivities (e.g., relative humidity and temperature), we present the first online calibration system designed specifically for low-cost air quality sensors to calibrate zero and span concentrations at hourly to weekly intervals. Monitors are tested and validated in a number of environments across multiple outdoor and indoor sites in New Haven, CT; Baltimore, MD; and New York City. The evaluated pollutants (O3, NO2, NO, CO, CO2, and PM2.5) performed well against reference instrumentation (e.g., r = 0.66–0.98) in urban field evaluations with fast e-folding response times (≤1 min), making them suitable for both large-scale network deployments and smaller-scale targeted experiments at a wide range of temporal resolutions. We also provide a discussion of best practices on monitor design, construction, systematic testing, and deployment

Health Risk Characterization for Transport Users and Workers: Community Health and Cumulative Risk Considerations

69A3551747128We conducted an exposure assessment for consumers to characterize benzene (and other volatile organic compounds) exposure associated with vehicle refueling using modern sampling and analysis methodologies. The consumer exposure assessment data were extended to an occupational setting by developing worker exposure scenarios to estimate excess risk values for gasoline service station attendants and pump attendants. The risk assessment results for the consumers were then put in a holistic health context including an analysis of other individual, community, and socio-economic factors (a cumulative risk characterization). While benzene exposure during refueling was not a major cancer contributor, cancer risk was found to be a concern due to exposures to ambient air toxics. Transportation-related sources contributed to four of the five top air toxic carcinogens identified. Cancer is a major cause of death in all participant communities and half of the study participants resided in communities where challenging socio-economic conditions have potential to increase cancer mortality overall and reduce survival times for cancer patients. This cumulative risk characterization found cancer risk to be a concern in both the ambient environmental and community settings suggesting a management approach targeting both the exposure and community context