Ice-nucleating particles (INPs) in biomass-burning aerosol (BBA) that affect cloud glaciation, microphysics, precipitation, and radiative forcing were recently found to be driven by the production of mineral phases. BBA experiences extensive chemical aging as the smoke plume dilutes, and we explored how this alters the ice activity of the smoke using simulated atmospheric aging of authentic BBA in a chamber reactor. Unexpectedly, atmospheric aging enhanced the ice activity for most types of fuels and aging schemes. The removal of organic carbon particle coatings that conceal the mineral-based ice-active sites by evaporation or oxidation then dissolution can increase the ice activity by greater than an order of magnitude. This represents a different framework for the evolution of INPs from biomass burning where BBA becomes more ice active as it dilutes and ages, making a larger contribution to the INP budget, resulting cloud microphysics, and climate forcing than is currently considered.

The mineralogical and immersion-mode freezing properties of volcanic ashes from three volcanoes, Volcań de Fuego and Santiaguito in Guatemala, and Soufriere Hills Volcano, in Montserrat, were examined. All ashes (sieved to <37 μm) contained effective ice nuclei, typically freezing over the temperature range of −12 to −25 °C and possessing ice active site densities (n s ) spanning ∼10 1 to 10 5 cm −2 over this temperature range. The high freezing activity of the ashes was determined to likely originate from pyroxene minerals, and the ice nucleation properties of pyroxene minerals are also reported here for the first time for comparison. Ca-and Narich plagioclase feldspars also contributed to the observed freezing properties. Volcanic glass was present in all of the samples and is theorized to be a much weaker ice nucleant, effectively diluting the freezing ability of the crystalline mineral phases. Smaller particle size fractions of the Volcań de Fuego ash were observed to contain more active ice nucleating particles, attributed to an increase in the amount of pyroxene minerals with decreasing particle size fraction. The particle resuspension and size segregated collection process was also observed to increase the ice nucleating ability of all size fractions, likely due to mechanical ablation removing passivated surfaces and exposing fresher and more ice-active mineral surfaces.

Volcanic ash nucleates ice when immersed in supercooled water droplets, giving it the potential to influence weather and climate from local to global scales. This ice nucleation activity (INA) is...

Abstract. A suite of generally applicable statistical methods based on empirical bootstrapping is presented for calculating uncertainty and testing the significance of quantitative differences in temperature and/or ice active site densities between ice nucleation temperature spectra derived from droplet freezing experiments. Such experiments are widely used to determine the heterogeneous ice nucleation properties and ice nucleation particle concentration spectra of different particle samples, as well as in studies of homogeneous freezing. Our methods avoid most of the assumptions and approximations inherent to existing approaches and if used properly can capture the full range of random variability and error in ice nucleation spectra. Applications include calculation of accurate confidence intervals and confidence bands, quantitative statistical testing of differences between observed freezing spectra, accurate subtraction of the background filtered water freezing signal, and calculation of a range of statistical parameters using data from a single droplet array freezing experiment if necessary. By improving the statistical tools available, this work will improve the quality and accuracy of future ice nucleation research and will allow quantitative comparisons of the ice nucleation ability of different particles and surfaces.

Abstract. A suite of generally applicable statistical methods based on empirical bootstrapping is presented for calculating uncertainty and testing the significance of quantitative differences in temperature and/or ice active site densities between ice nucleation temperature spectra derived from droplet freezing experiments. Such experiments are widely used to determine the heterogeneous ice nucleation properties and ice nucleation particle concentration spectra of different particle samples, as well as in studies of homogeneous freezing. Our methods avoid most of the assumptions and approximations inherent to existing approaches, and when sufficiently large sample sizes are used (approximately >150 droplets and >=1000 bootstrap samples in our system), can capture the full range of random variability and error in ice nucleation spectra. Applications include calculation of accurate confidence intervals and confidence bands, quantitative statistical testing of differences between observed freezing spectra, accurate subtraction of the background filtered water freezing signal, and calculation of a range of statistical parameters using data from a single droplet array freezing experiment if necessary. By providing additional statistical tools to the community, this work will improve the quality and accuracy of statistical tests and representations of uncertainty in future ice nucleation research, and will allow quantitative comparisons of the ice nucleation ability of different particles and surfaces.