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

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

Atmospheric Measurements of Submicron Aerosols at the California-Mexico Border and in Houston, Texas

Using an innovative arrangement of instruments to obtain a comprehensive set of properties, we present a description of the submicron aerosol properties for two distinct regions. During the 2009 SHARP/SOOT campaign in Houston, TX, the average effective density was 1.54 ± 0.07 g cm^-3, consistent with a population comprised largely of sulfates and organics Even in low concentrations (0.31 ± 0.22 µg m^-3), black carbon concentration has a significant impact on the overall density and optical properties. Under prevailing northerly winds, the average black carbon concentration increases from 0.26 ± 0.18 µg m^-3 to 0.60 ± 0.21 µg m^-3. Throughout the campaign, aerosols are often internally mixed, with one peak in the effective density distribution located at 1.55 ± 0.07 g cm^-3. In addition, we conclude that in this region the meteorology has a discernible impact on the concentration and properties of aerosols. After a frontal passage, there is a significant shift in the size distribution as the concentration of <100 nm particles increase and the average effective density decreases to 1.43 ± 0.08 g cm^-3. In Tijuana, Mexico, the submicron aerosols are heavily influenced by vehicle emissions. We observe an average single scattering albedo of 0.75. This average SSA is lower than observed in many US urban environments, and indicates a high concentration of black carbon. The average black carbon concentration is 2.71 ± 2.65 g cm^-3. The aerosol size distributions reveal a high concentration of small particles (< 100 nm) during the day, which are frequently associated with vehicle emissions. Overall, 46 and 81 nm particles are hydrophobic, have an average effective near 1.30 g cm^-3, a higher volatile growth factors than the larger particles, and exhibit a distinct diurnal cycle, which, on average, ranges between 0.80 during the afternoon and 1.70 g cm^-3 overnight. 46 and 81 nm distributions indicate a uniform aerosol composition. 151 and 240 nm aerosols are less cyclical, and the hygroscopicity, volatility, and effect density distributions all exhibit a bimodal distribution, which indicates an external mixture of aerosols. Black carbon and vehicle and industrial organic emissions appear to be the main components of the external mixture

Measurements of Submicron Aerosols at the California-Mexico Border during the Cal-Mex 2010 Field Campaign

We present measurements of submicron aerosols in Tijuana, Mexico during the Cal-Mex 2010 field campaign. A suite of aerosol instrumentations were deployed, including a hygroscopic-volatility tandem differential mobility analyzer (HV-TDMA), aerosol particle mass analyzer (APM), condensation particle counter (CPC), cavity ring-down spectrometer (CRDS), and nephelometer to measure the aerosol size distributions, effective density, hygroscopic growth factors (HGF), volatility growth factors (VGF), and optical properties. The average mass concentration of PM0.6 is 10.39 +/- 7.61 1.mu g m(-3), and the derived average black carbon (BC) mass concentration is 2.87 +/- 2.65 mu g m(-3). There is little new particle formation or particle growth during the day, and the mass loading is dominated by organic aerosols and BC, which on average are 37% and 27% of PM1.0, respectively. For four particle sizes of 46, 81,151, and 240 nm, the measured particle effective density, HGFs, and VGFs exhibit distinct diurnal trends and size-dependence. For smaller particles (46 and 81 mm), the effective density distribution is unimodal during the day and night, signifying an internally mixed aerosol composition. In contrast, larger particles (151 and 240 nm) exhibit a bi-modal effective density distribution during the daytime, indicating an external mixture of fresh BC and organic aerosols, but a unimodal distribution during the night, corresponding to an internal mixture of BC and organic aerosols. The smaller particles show a noticeable diurnal trend in the effective density distribution, with the highest effective density (1.70 g cm(-3)) occurring shortly after midnight and the lowest value (0.90 g cm(-3)) occurring during the afternoon, corresponding most likely to primary organic aerosols and BC, respectively. Both HGFs and VGFs measured are strongly size-dependent. HGFs increase with increasing particle size, indicating that the largest particles are more hygroscopic. VGFs decrease with increasing particle size, indicating that larger particles are more volatile. The hygroscopicity distributions of smaller particles (46 and 81 nm) are unimodal, with a HGF value close to unity. Large particles typically exhibit a bi-modal distribution, with a non-hygroscopic mode and a hygroscopic mode. For all particle sizes, the VGF distributions are bimodal, with a primary non-volatile mode and a secondary volatile mode. The average extinction, scattering, and absorption coefficients are 86.04, 63.07, and 22.97 Mm(-1), respectively, and the average SSA is 0.75. Our results reveal that gasoline and diesel vehicles produce a significant amount of black carbon particles in this US Mexico border region, which impacts the regional environment and climate. Published by Elsevier Ltd

Measurements of submicron aerosols at the California-Mexico border during the Cal-Mex 2010 field campaign

We present measurements of submicron aerosols in Tijuana, Mexico during the Cal-Mex 2010 field campaign. A suite of aerosol instrumentations were deployed, including a hygroscopic-volatility tandem differential mobility analyzer (HV-TDMA), aerosol particle mass analyzer (APM), condensation particle counter (CPC), cavity ring-down spectrometer (CRDS), and nephelometer to measure the aerosol size distributions, effective density, hygroscopic growth factors (HGF), volatility growth factors (VGF), and optical properties. The average mass concentration of PM0.6 is 10.39 +/- 7.61 1.mu g m(-3), and the derived average black carbon (BC) mass concentration is 2.87 +/- 2.65 mu g m(-3). There is little new particle formation or particle growth during the day, and the mass loading is dominated by organic aerosols and BC, which on average are 37% and 27% of PM1.0, respectively. For four particle sizes of 46, 81,151, and 240 nm, the measured particle effective density, HGFs, and VGFs exhibit distinct diurnal trends and size-dependence. For smaller particles (46 and 81 mm), the effective density distribution is unimodal during the day and night, signifying an internally mixed aerosol composition. In contrast, larger particles (151 and 240 nm) exhibit a bi-modal effective density distribution during the daytime, indicating an external mixture of fresh BC and organic aerosols, but a unimodal distribution during the night, corresponding to an internal mixture of BC and organic aerosols. The smaller particles show a noticeable diurnal trend in the effective density distribution, with the highest effective density (1.70 g cm(-3)) occurring shortly after midnight and the lowest value (0.90 g cm(-3)) occurring during the afternoon, corresponding most likely to primary organic aerosols and BC, respectively. Both HGFs and VGFs measured are strongly size-dependent. HGFs increase with increasing particle size, indicating that the largest particles are more hygroscopic. VGFs decrease with increasing particle size, indicating that larger particles are more volatile. The hygroscopicity distributions of smaller particles (46 and 81 nm) are unimodal, with a HGF value close to unity. Large particles typically exhibit a bi-modal distribution, with a non-hygroscopic mode and a hygroscopic mode. For all particle sizes, the VGF distributions are bimodal, with a primary non-volatile mode and a secondary volatile mode. The average extinction, scattering, and absorption coefficients are 86.04, 63.07, and 22.97 Mm(-1), respectively, and the average SSA is 0.75. Our results reveal that gasoline and diesel vehicles produce a significant amount of black carbon particles in this US Mexico border region, which impacts the regional environment and climate.</p