EXINPNSA

Accurate and temporally sensitive measurement of arctic ice-nucleating particle (INP) concentrations is a key challenge in understanding arctic aerosol-cloud interactions because they are quite variable depending on ambient conditions. High variability of arctic INPs have been reported in many of previous studies. Further, previous studies also found that the composition of arctic INPs varies, but it typically includes glacial outwash origin dust, dust-related minerals, pollution aerosol, and biogenic nuclei from the ocean and marine microlayers. It is therefore important to comprehensively study a realistic representation of both INP concentration and composition and their relevance to the aerosol-cloud interactions in the Arctic. To date, there are only a few reports of the short-term arctic INP from the Atlantic sector, though systematically assessed INP data are not available (a critical gap I will address). Particularly, we lack reasonably time-resolved data regarding the abundance and composition of atmospheric INPs in the Arctic at temperatures above about -15 ˚C. I propose to fill this gap by using measurements from the Atmospheric Radiation Measurement (ARM) atmospheric observatories. In particular, the detailed ARM and adjacent National Oceanic and Atmospheric Administration (NOAA) Barrow Atmospheric Baseline Observatory (BRW site hereafter) data of aerosol chemical composition speciation, abundance, cloud condensation nuclei (CCN) activity, and hygroscopicity are of the utmost importance for a better understanding of INPs’ mixing state as well as their implications in cloud, precipitation, and regional weather.

To complement the current ARM and NOAA BRW capabilities, I will experimentally characterize abundance and physicochemical properties of ambient INPs at ARM’s North Slope of Alaska (NSA) site during summer-fall 2020 as part of a two-fold study (i.e., the multi-year remote observation campaign will directly follow, and the second campaign would last until 2023). My team will make finely time-resolved online INP measurements (i.e., approximately every 8 min INP data point) at T > -15 °C. Different INP episodes will be assessed to help understand mixed-phase cloud systems typically observed in this region. Further, my field campaign and laboratory analyses will generate the data to understand how particle chemical composition and mixing state influence ambient ice-nucleation propensity at the NSA site. In general, such a data set has long been a missing piece in the study area of cloud microphysics and atmospheric chemistry and is important to improve atmospheric models of cloud feedbacks and determine their impact on the global radiative energy budget. The research questions that I want to address include (but are not limited to):

• Elucidating sources, abundance, chemical composition and ice-nucleation processes of high-temperature INPs at the NSA/BRW site
• Examining if immersion and/or condensation freezing, requiring a water saturation condition or CCN activation prior to ice nucleation, is a more predominant ice-nucleation mechanism at the NSA/BRW site
• Determining what ice nucleation pathway is the most sensitive to the chemical mixing state of ambient aerosol at the NSA/BRW site.

Timeline