This poster presents immersion freezing efficiencies of ambient particles collected from different latitudes between 79 °N and 75 °S. We collected particles using aerosol impactors at five different geographic locations, including i) the Atlantic sector of the Arctic, ii) an urban area in Europe, iii) a rural location in the U.S., iv) a mid-latitude agricultural site in the U.S., and v) the Antarctica peninsula area around Weddell Sea, representing unique particle episodes and atmospheric conditions. Then, we used an offline droplet-freezing assay instrument to measure fine-temperature-resolved ice-nucleating particle (INP) concentrations at T > -25 °C (with a detection capability of >0.0001 per L of air) for each region. Our preliminary results show INP concentrations in polar regions are - as expected - lower compared to mid-latitudes. Low concentrations of high-latitude INPs have been reported in other previous studies (e.g., Bigg et al., 2001; Rogers, 1996; Fountain and Ohtake, 1985; Mason et al., 2015; Ardon-Dryer and Levin, 2014; Belosi and Santachiara, 2014). Another important observation is the high variability of mid-latitude INP concentrations. A difference in the aerosol episode and properties may be key for such a high variability in the mid-latitude region. The composition of INPs varies, but it typically includes dust-related minerals, pollution aerosol, biogenic nuclei and marine microlayers. It is therefore important to comprehensively study realistic representation of both INP concentration and composition (ultimately for model parameterization) and their relevance to the aerosol-cloud interactions with a better temporal resolution under different atmospheric states and a wider spatial coverage of INP sampling sites (see Fig. 1). References: Ardon-Dryer, K. and Levin, Z.: Atmos. Chem. Phys., 14, 5217-5231, 2014. Belosi, F., and Santachiara, G.: Atmos. Res., 145–146, 105–111, 2014. Bigg, E. K.: Tellus B, 48, 223–233, 1996. Fountain, A. G., and Ohtake, T.: 1985: Climate Appl. Meteor., 24, 377–382, 1985. Mason, R. H. et al.: Atmos. Chem. Phys., 16, 1637–1651, 2016. Rogers, D. C. et al.: J. Atmos. Oceanic Technol., 18, 725–741, 2001.

Background: Asthma exacerbations, a common reason for Pediatric Emergency Department (PED) referral, can be triggered by multiple factors, including infections, air pollution and allergens. Lockdown measures and other public health interventions during the SARS-CoV-2 pandemic determined radical changes to behavioral and social habits, that were reflected by a reduction in the transmission of all respiratory pathogens and in the emissions of relevant air pollution anthropogenic sources. Objective: This study aims to describe how restrictions during SARS-CoV-2 pandemic impacted the PED referral for asthma exacerbations and their potentially associated environmental triggers in densely populated urban areas. Methods: PED referrals for acute asthma from 2015 to 2020 were compared to air pollution and pollen data. To this purpose, historical daily concentration records of PM2.5, PM10 (including specific chemical tracers), as well as NO2, C6H6, tree, grass and weed pollen were analyzed. Results: In 2020, asthma-related PED referrals decreased up to 85%, compared to the average referral rate of the previous 5 years (P<0.01). The drastic drop in PED referrals was associated with a reduction of high-priority cases by 50-60%, unlike PED referrals for overall diagnoses, showing a larger contribution for severe outcomes. A concomitant diminished contribution of traffic-related air pollution was shown. Conclusions: The lower rate of asthma exacerbations in childhood can be related to synergic interactions of the multiple effects of lockdown measures which induced lower viral infection rates and decreased exposure to outdoor allergens. The reduction of traffic-related air pollution determined a weakening of inflammatory properties of urban PM.