The Fukushima Daiichi Nuclear Power Plant accident in Japan resulted in the emission of many radioactive cesium (Cs)-containing particles that have charges on the surface due to self-charging. ...Charged aerosol particles are efficiently deposited inside human airways, leading to adverse health effects. To evaluate these effects, we developed a technique for estimating the charge number (n
p
) of radioactive particles by measuring the surface potentials (V
p
) of individual radioactive particles using Kelvin probe force microscopy. The V
p
values of the individual CsCl particles were highly correlated with the surface n
p
, indicating that V
p
is a measure of the charged aerosol state. To further examine the V
p
-n
p
relationship, a simplified capacitance model was developed to estimate the ratio of V
p
to n
p
per unit area of particles. Although the calculated V
p
was proportional to the n
p
, consistent with our experiment, the calculated ratio was higher than those determined experimentally. The magnitude of this ratio may depend on the conductivity, microphysical properties and chemical composition of the particles. Despite these uncertainties, the experimentally determined V
p
-n
p
relationship of the CsCl particles was used to estimate the n
p
of the radioactive and non-radioactive particles from the measurement of the V
p
of these particles. It was demonstrated that the n
p
of the radioactive particles was much higher than that of the non-radioactive particles, suggesting that radioactive particles are efficiently charged by self-charging. These charged radioactive particles may strongly cause adverse human health effects owing to their efficient deposition in human airways.
Below-cloud scavenging coefficients for ultrafine particles (UFP) exhibit comparatively large uncertainties in part because of the limited availability of observational data sets from which robust ...parameterizations can be derived or that can be used to evaluate output from numerical models. Long time series of measured near-surface UFP size distributions and precipitation intensity from the Midwestern USA are used here to explore uncertainties in scavenging coefficients and test both the generalizability of a previous empirical parameterization developed using similar data from a boreal forest in Finland (Laakso et al., 2003) and whether a more parsimonious formulation can be developed. Scavenging coefficients (λ) over an ensemble of 95 rain events (with a median intensity of 1.56 mm h−1) and 104 particle diameter (Dp) classes (from 10 to 400 nm) indicate a mean value of 3.4 × 10−5 s−1 (with a standard error of 1.1 × 10−6 s−1) and a median of 1.9 × 10−5 s−1 (interquartile range: −2.0 × 10−5 to 7.5 × 10−5 s−1). The median scavenging coefficients for Dp: 10–400 nm computed over all 95 rain events exhibit close agreement with the empirical parameterization proposed by (Laakso et al., 2003). They decline from ∼4.1 × 10−5 s−1 for Dp of 10–19 nm, to ∼1.6 × 10−5 s−1 for Dp of 80–113 nm, and show an increasing tendency for Dp > 200 nm.
•Below-cloud scavenging coefficients derived from long-term particle measurements.•Scavenging coefficients decline by three as diameter goes from 15 nm to 100 nm.•Good agreement with empirical parameterization of Laakso et al. (2003).
Haze particles as a key air pollutant contain high level of toxins, which were hypothesized to inhibit phytoplankton growth when deposited to the ocean, and thus indirectly affect the climate. ...However, field observations have yet to provide conclusive evidence to confirm this hypothesis. Onboard microcosm experiments in the Northwest Pacific Ocean (NWPO) show that haze particles collected at the East Asia continent had an inhibition impact on phytoplankton growth only when at very high particle loading (2 mg/L). In contrast, haze particles at low and medium loadings (0.03–0.6 mg/L) stimulated phytoplankton growth and shifted phytoplankton size structure toward larger cells, primarily due to the supply of inorganic nitrogen nutrients from the particles. Model simulations showed that haze particle loading in NWPO surface seawater was usually more than an order of magnitude lower than 2 mg/L. This indicates that haze particles are unlikely to cause harm but to stimulate phytoplankton growth in the nitrogen‐limited NWPO. Ocean biogeochemical modeling further shows that deposited nitrogen significantly enhanced surface ocean chlorophyll a concentration in the winter and spring of 2014. Overall, these results demonstrate that haze particles stimulate rather than inhibit primary production in the NWPO.
Plain Language Summary
Increasing anthropogenic emissions of air pollutants from fast‐developing East Asia leads to increasing deposition of aerosol particles to the Northwest Pacific Ocean (NWPO). Such particles contain both nutrients such as nitrogen and phosphorus and toxins such as copper and organic pollutants to the marine phytoplankton, which have contrasting effects on marine ecosystems and carbon uptake. However, the actual impact remains unknown. Detailed onboard incubation experiments confirm that Chinese haze particles have an overall stimulation effects on phytoplankton under representative ocean conditions in NWPO. Toxicity to phytoplankton is only observed when the added haze particle concentration is unrealistically high. Simulations suggest that nitrogen in the atmospheric deposition contributes significantly to the surface chlorophyll a concentration in NWPO and enhances carbon fixation, which indirectly offsets global warming.
Key Points
Toxicity of haze particle is observed only at unrealistically high concentrations (2 mg/L) in the seawater
Haze particles at low to medium loading (0.03–0.6 mg/L) stimulated phytoplankton growth and shifted phytoplankton size structure toward larger cells
Deposition of haze particles under realistic environmental conditions stimulates primary production in the Northwest Pacific Ocean
What concentration of ice‐nucleating particles is required to completely glaciate a typical atmospheric supercooled liquid cloud? This seemingly esoteric question has far reaching implications, as ...the ratio of liquid to ice in these clouds governs, for example, their influence on Earth's radiation budget and their precipitation efficiency. Microphysical properties of steady‐state mixed‐phase clouds formed in a laboratory convection chamber are observed using digital holography. It is observed that the ratio of ice to total water content of steady‐state mixed‐phase clouds is determined by the concentration of ice‐nucleating aerosol particles. Existing theory is adapted to show such clouds result from a balance between the thermodynamic forcing (i.e., the source of excess water vapor that is condensing to liquid and ice) and the number and size of particles that become ice (i.e., the ice integral radius). The measurements quantitatively support the Korolev‐Mazin conditions for existence of mixed‐phase clouds.
Key Points
Holographic measurements of steady‐state mixed‐phase clouds are made in a laboratory cloud‐convection chamber
The ice fraction in the cloud is determined by varying the ice‐nucleating particle concentration while holding CCN concentration constant
Measurements are in agreement with an extension of Korolev‐Mazin theory for critical forcing needed for mixed‐phase conditions
A common feature of polar liquid‐bearing clouds (LBCs) is radiatively driven turbulence, which may variously alter cloud lifecycle via vertical mixing, droplet activation, and subsequent feedbacks. ...However, polar LBCs are commonly initiated under stable, nonturbulent conditions. Using long‐term data from the North Slope of Alaska and McMurdo, Antarctica, we show that nonturbulent conditions prevail in ~25% of detected LBCs, surmised to be preferentially early in their lifecycle. We conclude that nonturbulent LBCs are likely common over the polar regions owing primarily to atmospheric temperature and stability. Such stable environments are known to support gravity wave activity. Using large‐eddy simulations, we find that short to intermediate period gravity waves may catalyze turbulence formation when aerosol particles available for activation are sufficiently small. We posit that the frequent occurrence of nonturbulent LBCs over the polar regions has implications for polar aerosol‐cloud interactions and their parameterization in large‐scale models.
Plain Language Summary
The presence of turbulent mixing in liquid‐containing polar clouds is commonly presupposed, but here, we show that a quarter of all liquid‐containing clouds over the North Slope of Alaska and McMurdo Station, Antarctica, are nonturbulent. Many of these nonturbulent clouds are likely in the first stages of their lifecycle after forming in stable, nonturbulent atmospheric layers. Unlike their often more mature counterparts, these nonturbulent clouds are frequently not very efficient at cooling themselves by radiating thermal energy, which among other factors, prolongs the time required to develop turbulence. Using model simulations, we show that oscillating vertical motions of air that are common under stable atmospheric conditions may enhance the formation and growth of cloud droplets such that the cloud radiative cooling efficiency becomes higher, which ultimately hastens turbulence formation. We conclude that it is likely necessary to properly represent a number of atmospheric parameters that control the concentration of cloud droplets, as well as the regional properties of the oscillating vertical air motions, to faithfully represent the polar atmosphere in regional and global models.
Key Points
Nonturbulent conditions occur in a quarter of liquid‐bearing clouds over the North Slope of Alaska and McMurdo, Antarctica
Nonturbulent clouds are likely common over polar regions owing to atmospheric stability, which also supports gravity wave (GW) activity
When aerosol particles available to be activated are relatively small, GWs can enhance droplet numbers and turbulence formation
Previous studies have revealed a negative correlation between the East Asian winter monsoon and wintertime haze‐fog events in China. The winter monsoon reduces haze‐fog by advecting away aerosol ...particles and supplying clean air through cold waves. However, it is found that the frequency of haze‐fog events on subseasonal time scales displays no correlation with typical winter monsoon indices. The results show that the accumulating and maintaining effects of calm weather related to the Siberian High, which is also a part of the monsoon circulation system, are equally important for the development of haze‐fog events during winter. Correlation analysis indicates that subseasonal variations in haze‐fog are closely related to the intensity of the Siberian High (r = 0.49). The Siberian High may increase the occurrence of haze‐fog events by reducing the near surface wind speed and enhancing the stratification stability. To quantify the contribution of these diverse effects of the winter monsoon on the variations in haze‐fog events, we analyzed haze‐fog events during periods of cold wave activity and calm weather separately and contrasted the relative contributions of these two effects on different time scales. On the subseasonal scale, the effect of the Siberian High was 2.0 times that of cold waves; on the interannual scale, the effect of cold waves was 2.4 times that of the Siberian High. This study reveals the dual effects of the East Asian winter monsoon on wintertime haze‐fog variations in eastern China and provides a more comprehensive understanding of the relationship between the monsoon and haze‐fog events.
Key Points
The Siberian High and cold waves have opposite effects on wintertime haze‐fog variations
The Siberian High is the dominant factor that controls monthly haze‐fog variations
The influence of the Siberian High on haze‐fog events will become more important in the future
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