Abstract
Quantitative simulation of an aerosol’s lifecycle by regional-scale and global-scale atmospheric models is mandatory for unbiased analysis and prediction of aerosol radiative forcing and ...climate change. Globally, aerosol deposition is dominated by the rainout process, which is mostly triggered by activation of aerosols to liquid droplets in supersaturated domains of precipitating clouds. However, the actual environmental supersaturation value that aerosols experience in precipitating clouds is difficult for models to predict, and it has never been constrained by observations; as a result, there is large uncertainty in atmospheric aerosol simulations. Here, by a particle-tracer analysis of 37 rainfall events in East Asia, near the largest source region of anthropogenic aerosols in the northern hemisphere, we observed that the environmental supersaturation actually experienced by the removed aerosols in precipitating clouds averaged 0.08 ± 0.03% and ranged from 0.03 to 0.2%. Simulations by a mixing-state-resolved global aerosol model showed that the simulated long-range transport efficiency and global atmospheric burden of black carbon aerosols can be changed by a factor of two or three as a result of a change in the environmental supersaturation in precipitating clouds within just 0.08 ± 0.03%. This result is attributable to the fact that the sensitivity of an aerosol’s rainout efficiency to environmental supersaturation is higher for the less-aged black carbon concentrated near source regions. Our results suggest that observational constraints of environmental supersaturation in precipitating clouds, particularly near source regions, are of fundamental importance for accurate simulation of the atmospheric burden of black carbon and other aerosols.
We demonstrate a new method to measure refractive indices
m of small nonspherical particles by simultaneous measurement of particle volume and light-scattering cross section. In contrast to ...traditional methods, this method can suppress uncertainties due to unknown particle shape. As demonstration of the method, laboratory experiments using an aerosol particle mass analyzer (APM) and single-particle soot photometer (SP2) have been conducted to determine the refractive indices of seven types of commercial black carbon particles and ambient soot at 1064
nm wavelength. Difference in measured |(
m
2−1)/(
m
2+2)| values among the seven commercial black carbon samples is consistent with the difference in their crystalline structures identified by a transmission electron microscope. The complex refractive index
m=(
n,
k) of ambient soot particles in Tokyo urban area was determined to be
m=(2.26±0.13, 1.26±0.13).
Black carbon (BC) particles cause adverse health effects and contribute to the heating of the atmosphere by absorbing visible solar radiation. Efforts have been made to reduce BC emissions, ...especially in urban areas; however, long-term measurements of BC mass concentration (MBC) are very limited in Japan. We report MBC measurements conducted in Tokyo from 2003 to 2017, showing that MBC decreased by a factor of 3 from 2003 to 2010 and was stable from 2010 to 2017. Fine particulate concentrations (PM2.5) decreased by a much smaller factor during 2003–2010. The diurnal variations of BC size distributions suggest that the BC in Tokyo originates mainly from local sources, even after 2010. Our three-dimensional model calculations show that BC from the Asian continent contributes a small portion (about 20%) of the annual average MBC in the Kanto region of Japan, which includes Tokyo. This indicates that continued reduction of BC emissions inside Japan should be effective in further decreasing MBC.
Reliable measurement of the size-resolved number concentration (size distribution) of solid particles dispersed in water or melted ice is of critical importance in many geoscientific observational ...studies. Because physical and chemical properties of particles can be measured more unambiguously and accurately in rarefied media (air) than in condensed media (water), particle measurement after aerosolization using a nebulizer is a significant method for the observation of solid particles dispersed in water. We propose a mathematical theory for estimating the original size distribution of solid particles in water from the measured size distribution of aerosolized particles. We assume that the size distribution of water droplets produced by a nebulizer is given. The size distribution of solid particles in water can be estimated by solving a system of nonlinear equations. The complexity in solving the equations increases rapidly with the computational resolution of particle size and the assumed maximum number of particles within each droplet. For such a system of equations, we found rigorous error bounds of a true solution using INTLAB, an interval arithmetic package. Our theoretical framework will be useful in many fields in geoscience as a fundamental scheme to quantify solid particles in water. In particular, an application of the proposed theoretical method is shown to be useful for the quantitative observations of the size distribution of black carbon particles in rainwater.
•Accurate measurement of size distribution of solid particles in water.•We assume a use of nebulizer to aerosolize solid particles in water.•We model the stochastic agglomerations of particles upon nebulization.
Black carbon (BC) plays an important role in the climate system because of its strong warming effect, yet the magnitude of this effect is highly uncertain owing to the complex mixing state of ...aerosols. Here we build a unified theoretical framework to describe BC's mixing states, linking dynamic processes to BC coating thickness distribution, and show its self-similarity for sites in diverse environments. The size distribution of BC-containing particles is found to follow a universal law and is independent of BC core size. A new mixing state module is established based on this finding and successfully applied in global and regional models, which increases the accuracy of aerosol climate effect estimations. Our theoretical framework links observations with model simulations in both mixing state description and light absorption quantification.
Long-term measurements of atmospheric mass concentrations
of black carbon (BC) are needed to investigate changes in its emission,
transport, and deposition. However, depending on instrumentation, ...parameters
related to BC such as aerosol absorption coefficient (babs) have been
measured instead. Most ground-based measurements of babs in the Arctic
have been made by filter-based absorption photometers, including particle
soot absorption photometers (PSAPs), continuous light absorption photometers
(CLAPs), Aethalometers, and multi-angle absorption photometers (MAAPs). The
measured babs can be converted to mass concentrations of BC (MBC) by
assuming the value of the mass absorption cross section (MAC; MBC= babs/ MAC). However, the accuracy of conversion of babs to MBC
has not been adequately assessed. Here, we introduce a systematic method for
deriving MAC values from babs measured by these instruments and
independently measured MBC. In this method, MBC was measured with a
filter-based absorption photometer with a heated inlet (COSMOS).
COSMOS-derived MBC (MBC (COSMOS)) is traceable to a rigorously
calibrated single particle soot photometer (SP2), and the absolute accuracy
of MBC (COSMOS) has been demonstrated previously to be about 15 % in
Asia and the Arctic. The necessary conditions for application of this method
are a high correlation of the measured babs with independently measured
MBC and long-term stability of the regression slope, which is denoted
as MACcor (MAC derived from the correlation). In general,
babs–MBC (COSMOS) correlations were high (r2= 0.76–0.95 for
hourly data) at Alert in Canada, Ny-Ålesund in Svalbard, Barrow (NOAA Barrow Observatory) in
Alaska, Pallastunturi in Finland, and Fukue in Japan and stable for up to
10 years. We successfully estimated MACcor values (10.8–15.1 m2 g−1 at a wavelength of 550 nm for hourly data) for these instruments,
and these MACcor values can be used to obtain error-constrained
estimates of MBC from babs measured at these sites even in the past,
when COSMOS measurements were not made. Because the absolute values of
MBC at these Arctic sites estimated by this method are consistent with
each other, they are applicable to the study of spatial and temporal
variation in MBC in the Arctic and to evaluation of the performance of
numerical model calculations.
Abstract
When meteorites impact the Earth’s atmosphere, they fractionalize and ablate, generating aerosol particles containing extraplanetary materials. Meteoritic materials have been identified ...among aerosol particles using elemental markers (iron and magnesium); however, their shapes and mixing states are largely unknown. Here we demonstrate the presence of meteoritic materials collected by a research aircraft from the troposphere over the western Pacific using transmission electron microscopy. The distribution of meteoritic elements within individual particles coincided with sulfur, indicating that they were in forms of sulfates, i.e., water-soluble. Enhanced number fractions of sulfate particles with meteoritic materials were observed during tropopause-folding events, suggesting that they originated from the stratosphere. We also estimated the potential contributions of the Chelyabinsk meteorite event, which occurred 5 months prior to the sampling and represents the largest meteorite event in the past century. This study provides unique observational evidence for the linkage between extraplanetary materials and tropospheric aerosols.
We conducted a detailed evaluation of a method for measuring the mass concentrations and size distributions of black carbon (BC) particles in rainwater and snow. The method uses an ultrasonic ...nebulizer (USN) and a single particle soot photometer (SP2). The USN disperses sample water into micron-size droplets at a constant rate and then dries them to release BC particles into the air. The masses of individual BC particles are measured by the SP2, using the laser-induced incandescence technique. The loss of BC particles during the extraction from liquid water to air depends on their sizes. We determined the size-dependent extraction efficiency using polystyrene latex (PSL) spheres with 12 different diameters between 107 and 1025 nm. The PSL concentrations in water were measured by the light extinction at 532 nm. The extraction efficiency of the USN showed a broad maximum of about 10% in the diameter range 200-500 nm and decreased substantially at larger sizes. The accuracy and reproducibility of the measured mass concentration of BC in sample water after long-term storage were about ±25% and ±35%, respectively. We tested the method by analyzing rainwater and surface snow samples collected in Okinawa and Sapporo, respectively. The measured number size distributions of BC in these samples showed negligible contributions of BC particles larger than 300 nm to the total number of BC particles. A dominant fraction of BC mass in these samples was observed in the diameter range 100-500 nm.
Copyright 2013 American Association for Aerosol Research
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