We report the first measurement of target single spin asymmetries in the semi-inclusive ${}^3\mathrm{He}(e,e^{\prime }{\pi }^{\pm })X$ reaction on a transversely polarized target. The experiment, conducted at Jefferson Lab using a 5.9 GeV electron beam, covers a range of $0.16<x<0.35$ with $1.4<Q^2<2.7{\mathrm{GeV}}^2$. The Collins and Sivers moments were extracted from the azimuthal angular dependence of the measured asymmetries. The ${\pi }^{\pm }$ Collins moments for ${}^3\mathrm{He}$ are consistent with zero, except for the ${\pi }^{+}$ moment at $x=0.35$, which deviates from zero by $2.3\sigma$. While the ${\pi }^{-}$ Sivers moments are consistent with zero, the ${\pi }^{+}$ Sivers moments favor negative values. The neutron results were extracted using the nucleon effective polarization and measured cross section ratios of proton to ${}^3\mathrm{He}$, and are largely consistent with the predictions of phenomenological fits and quark model calculations.

We report a new, high-precision measurement of the proton elastic form factor ratio μpGE/GM for the four-momentum transfer squared Q2=0.3–0.7(GeV/c)2. The measurement was performed at Jefferson Lab (JLab) in Hall A using recoil polarimetry. With a total uncertainty of approximately 1%, the new data clearly show that the deviation of the ratio μpGE/GM from unity observed in previous polarization measurements at high Q2 continues down to the lowest Q2 value of this measurement. The updated global fit that includes the new results yields an electric (magnetic) form factor roughly 2% smaller (1% larger) than the previous global fit in this Q2 range. We obtain new extractions of the proton electric and magnetic radii, which are 〈rE2〉1/2=0.875±0.010 fm and 〈rM2〉1/2=0.867±0.020 fm. The charge radius is consistent with other recent extractions based on the electron–proton interaction, including the atomic hydrogen Lamb shift measurements, which suggests a missing correction in the comparison of measurements of the proton charge radius using electron probes and the recent extraction from the muonic hydrogen Lamb shift

We report new measurements of the parity-violating asymmetry $A_{\mathrm{PV}}$ in elastic scattering of 3 GeV electrons off hydrogen and ${}^4\mathrm{He}$ targets with $⟨{\theta }_{\mathrm{lab}}⟩\approx 6.0°$. The ${}^4\mathrm{He}$ result is $A_{\mathrm{PV}}=\mathbf{(}+6.40\pm 0.23(\mathrm{stat})\pm 0.12(\mathrm{syst})\mathbf{)}\times {10}^{-6}$. The hydrogen result is $A_{\mathrm{PV}}=\mathbf{(}-1.58\pm 0.12(\mathrm{stat})\pm 0.04(\mathrm{syst})\mathbf{)}\times {10}^{-6}$. These results significantly improve constraints on the electric and magnetic strange form factors $G_E^s$ and $G_M^s$. We extract $G_E^s=0.002\pm 0.014\pm 0.007$ at $⟨Q^2⟩=0.077{\mathrm{GeV}}^2$, and $G_E^s+0.09G_M^s=0.007\pm 0.011\pm 0.006$ at $⟨Q^2⟩=0.109{\mathrm{GeV}}^2$, providing new limits on the role of strange quarks in the nucleon charge and magnetization distributions.

Brown carbon (BrC) is an organic aerosol material that preferentially absorbs light of shorter wavelengths. Global‐scale radiative impacts of BrC have been difficult to assess due to the lack of BrC observational data. To address this, aerosol filters were continuously collected with near pole‐to‐pole latitudinal coverage over the Pacific and Atlantic basins in three seasons as part of the Atmospheric Tomography Mission. BrC chromophores in filter extracts were measured. We find that globally, BrC was highly spatially heterogeneous, mostly detected in air masses that had been transported from regions of extensive biomass burning. We calculate the average direct radiative effect due to BrC absorption accounted for approximately 7% to 48% of the top of the atmosphere clear‐sky instantaneous forcing by all absorbing carbonaceous aerosols in the remote atmosphere, indicating that BrC from biomass burning is an important component of the global radiative balance.

The electric form factor of the neutron was determined from studies of the reaction ${\mathrm{}}^3\overrightarrow{\mathrm{He}}(\overrightarrow{e},e^{\prime }n)pp$ in quasielastic kinematics in Hall A at Jefferson Lab. Longitudinally polarized electrons were scattered off a polarized target in which the nuclear polarization was oriented perpendicular to the momentum transfer. The scattered electrons were detected in a magnetic spectrometer in coincidence with neutrons that were registered in a large-solid-angle detector. More than doubling the $Q^2$ range over which it is known, we find $G_E^n=0.0236\pm 0.0017(\mathrm{stat})\pm 0.0026(\mathrm{syst})$, $0.0208\pm 0.0024\pm 0.0019$, and $0.0147\pm 0.0020\pm 0.0014$ for $Q^2=1.72$, 2.48, and $3.41{\mathrm{GeV}}^2$, respectively.

Wildfires inject large amounts of black carbon (BC) particles into the atmosphere, which can reach the lowermost stratosphere (LMS) and cause strong radiative forcing. During a 14-month period of observations on board a passenger aircraft flying between Europe and North America, we found frequent and widespread biomass burning (BB) plumes, influencing 16 of 160 flight hours in the LMS. The average BC mass concentrations in these plumes (∼140 ng·m ⁻³ , standard temperature and pressure) were over 20 times higher than the background concentration (∼6 ng·m ⁻³ ) with more than 100-fold enhanced peak values (up to ∼720 ng·m ⁻³ ). In the LMS, nearly all BC particles were covered with a thick coating. The average mass equivalent diameter of the BC particle cores was ∼120 nm with a mean coating thickness of ∼150 nm in the BB plume and ∼90 nm with a coating of ∼125 nm in the background. In a BB plume that was encountered twice, we also found a high diameter growth rate of ∼1 nm·h ⁻¹ due to the BC particle coatings. The observed high concentrations and thick coatings of BC particles demonstrate that wildfires can induce strong local heating in the LMS and may have a significant influence on the regional radiative forcing of climate.