Cold Air Outbreaks Promote New Particle Formation Off the U.S. East Coast

Abstract

New particle formation (NPF) is the dominant contributor to total particle number concentration and significantly impacts the cloud condensation nuclei (CCN) budget (Kerminen et al., 2018;Merikanto et al., 2009). NPF occurs in diverse regions, ranging across urban, remote, and Arctic and polar areas (Kerminen et al., 2018;Schmale & Baccarini, 2021; Sellegri et al., 2019, and references therein). NPF has been observed in the boundary layer (BL) when influenced by biogenic (Häkkinen et al., 2013;Zhao et al., 2020) and anthropogenic sources (e.g., Siebert et al., 2004), in the free troposphere (FT; 3,000-15,000 m) where low temperatures and cloud processes provide favorable conditions for NPF (Clarke et al., 2013), and at the interface between the BL and FT (Dadashazar et al., 2018;Siebert et al., 2004). Several studies have also reported NPF in the lower FT (∼4,000 m) primarily driven by upward transport from the BL (Bianchi et al., 2016) or convective movement. In contrast to long-term ground-based studies (e.g.,

Dimethylamine in cloud water: a case study over the northwest Atlantic Ocean

“…It has been shown to be higher in winter 2020 ACTIVATE ights compared to summer and thus possibly helpful in explaining why there is more prevalent nucleation (e.g., more precursor concentrations such as SO 2 ). 53 Table 1 reinforces that CO is higher in winter, which is consistent with air mass trajectories being aligned with offshore ow. There was not a major difference in median CO levels between the two winter categories ($0.14 ppm), even though statistically, they were different (winter non-CAO > winter CAO).…”

“…As amines have been linked to new particle formation [116][117][118] it is important to note that winter CAO conditions (lower temperature and humidity) were most conducive to such events during ACTIVATE, 53 especially near clouds, with low temperatures and RH shown to be potentially contributing factors. Amines associated with nucleated particles can grow into sizes sufficiently large to activate into drops and thus be sampled as cloud water.…”

“…This study focuses on cloud water samples collected by the Falcon during the first two deployments in 2020: winter (14 February -12 March 2020) and summer (13 August -30 September 2020). We further divided the winter flights into two categories to isolate data on cold air outbreak (CAO) conditions, as recent work shows unique conditions in those flights affecting aerosol particles and clouds [53][54][55][56] . We used the same methods in recent ACTIVATE studies 53,57 to distinguish CAO days using a combination of Visible Infrared Imaging Radiometer Suite (VIIRS) imagery (NASA Worldview), flight reports, weather forecast data, and King Air dropsonde data.…”

“…Carbon monoxide is a tracer for anthropogenic emissions. It has been shown to be higher in winter 2020 ACTIVATE flights compared to summer and thus possibly helpful in explaining why there is more prevalent nucleation (e.g., more precursor concentrations such as SO 2 ) 53 . Table 1 reinforces that CO is higher in winter, which is consistent with air mass trajectories being aligned with offshore flow.…”

Relationships between supermicrometer particle concentrations and cloud water sea salt and dust concentrations: analysis of MONARC and ACTIVATE data

“…In contrast, ACTIVATE data reveal a drop-off in particle concentration above 1 km owing to the deeper MBL, especially in the wintertime when MBL heights typically exceed those of summertime by a few hundred meters. 49,70,71 Median concentrations were below 1 cm −3 within the MBL regardless of season. Fig.…”