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Abstract Wildfires in the western United States are large sources of particulate matter, and the area burned by wildfires is predicted to increase in the future. Some particles released from wildfires can affect cloud formation by serving as ice‐nucleating particles (INPs). INPs have numerous impacts on cloud radiative properties and precipitation development. Wildfires are potentially important sources of INPs, as indicated from previous measurements, but their abundance in the free troposphere has not been quantified. The Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen campaign sampled free tropospheric immersion‐freezing INPs from smoke plumes near their source and downwind, along with widespread aged smoke. The results indicate an enhancement of INPs in smoke plumes relative to out‐of‐plume background air, but the magnitude of enhancement was both temperature and fire dependent. The majority of INPs were inferred to be predominately organic in composition with some contribution from biological sources at modest super cooling, and contributions from minerals at deeper super cooling. A fire involving primarily sagebrush shrub land and aspen forest fuels had the highest INP concentrations measured in the campaign, which is partially attributed to the INP characteristics of lofted, uncombusted plant material. Electron microscopy analysis of INPs also indicated tar balls present in this fire. Parameterization of the plume INP data on a per‐unit‐aerosol surface area basis confirmed that smoke is not an efficient source of INPs. Nevertheless, the high numbers of particles released from, and ubiquity of western US wildfires in summertime, regionally elevate INP concentrations in the free troposphere.
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Ice-nucleating particle concentration measurements from Ny-Ålesund during the Arctic spring–summer in 2018
Abstract. In this study, we present atmospheric ice-nucleating particle (INP)concentrations from the Gruvebadet (GVB) observatory in Ny-Ålesund(Svalbard). All aerosol particle sampling activities were conducted in April–August 2018. Ambient INP concentrations (nINP) were measured for aerosolparticles collected on filter samples by means of two offline instruments:the Dynamic Filter Processing Chamber (DFPC) and the West Texas CryogenicRefrigerator Applied to Freezing Test system (WT-CRAFT) to assesscondensation and immersion freezing, respectively. DFPC measured nINPs for aset of filters collected through two size-segregated inlets: one fortransmitting particulate matter of less than 1 µm (PM1), theother for particles with an aerodynamic diameter of less than 10 µmaerodynamic diameter (PM10). Overall, nINPPM10 measured by DFPC ata water saturation ratio of 1.02 ranged from 3 to 185 m−3 attemperatures (Ts) of −15 to −22 ∘C. On average, the super-micrometer INP (nINPPM10-nINPPM1) accounted forapproximately 20 %–30 % of nINPPM10 in spring, increasing in summer to45 % at −22 ∘C and 65 % at −15 ∘C. This increase in super-micrometer INP fraction towards summer suggests that super-micrometeraerosol particles play an important role as the source of INPs in theArctic. For the same T range, WT-CRAFT measured 1 to 199 m−3. Althoughthe two nINP datasets were in general agreement, a notable nINP offset wasobserved, particularly at −15 ∘C. Interestingly, the results ofboth DFPC and WT-CRAFT measurements did not show a sharp increase in nINPfrom spring to summer. While an increase was observed in a subset of ourdata (WT-CRAFT, between −18 and −21 ∘C), the spring-to-summernINP enhancement ratios never exceeded a factor of 3. More evident seasonal variability was found, however, in our activated fraction (AF) data, calculated by scaling the measured nINP to the total aerosol particleconcentration. In 2018, AF increased from spring to summer. This seasonal AFtrend corresponds to the overall decrease in aerosol concentration towardssummer and a concomitant increase in the contribution of super-micrometer particles. Indeed, the AF of coarse particles resulted markedly higher thanthat of sub-micrometer ones (2 orders of magnitude). Analysis of low-traveling back-trajectories and meteorological conditions at GVB matched to our INP data suggests that the summertime INP population isinfluenced by both terrestrial (snow-free land) and marine sources. Ourspatiotemporal analyses of satellite-retrieved chlorophyll a, as well as spatial source attribution, indicate that the maritime INPs at GVB may comefrom the seawaters surrounding the Svalbard archipelago and/or in proximityto Greenland and Iceland during the observation period. Nevertheless,further analyses, performed on larger datasets, would be necessary to reachfirmer and more general conclusions.
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- Award ID(s):
- 1941317
- PAR ID:
- 10329922
- Date Published:
- Journal Name:
- Atmospheric Chemistry and Physics
- Volume:
- 21
- Issue:
- 19
- ISSN:
- 1680-7324
- Page Range / eLocation ID:
- 14725 to 14748
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)Abstract. Ice-nucleating particles (INPs) are efficiently removed fromclouds through precipitation, a convenience of nature for the study of thesevery rare particles that influence multiple climate-relevant cloudproperties including ice crystal concentrations, size distributions andphase-partitioning processes. INPs suspended in precipitation can be used toestimate in-cloud INP concentrations and to infer their originalcomposition. Offline droplet assays are commonly used to measure INPconcentrations in precipitation samples. Heat and filtration treatmentsare also used to probe INP composition and size ranges. Many previousstudies report storing samples prior to INP analyses, but little is knownabout the effects of storage on INP concentration or their sensitivity totreatments. Here, through a study of 15 precipitation samples collected at acoastal location in La Jolla, CA, USA, we found INP concentration changes upto > 1 order of magnitude caused by storage to concentrations ofINPs with warm to moderate freezing temperatures (−7 to−19 ∘C). We compared four conditions: (1) storage at roomtemperature (+21–23 ∘C), (2) storage at +4 ∘C, (3) storage at −20 ∘C and (4) flash-freezing samples with liquid nitrogen prior to storage at −20 ∘C. Results demonstrate that storage can lead to bothenhancements and losses of greater than 1 order of magnitude, withnon-heat-labile INPs being generally less sensitive to storage regime, butsignificant losses of INPs smaller than 0.45 µm in all tested storageprotocols. Correlations between total storage time (1–166 d) and changesin INP concentrations were weak across sampling protocols, with theexception of INPs with freezing temperatures ≥ −9 ∘C in samples stored at room temperature. We provide thefollowing recommendations for preservation of precipitation samples fromcoastal or marine environments intended for INP analysis: that samples bestored at −20 ∘C to minimize storage artifacts, thatchanges due to storage are likely an additional uncertainty in INPconcentrations, and that filtration treatments be applied only to freshsamples. At the freezing temperature −11 ∘C, average INPconcentration losses of 51 %, 74 %, 16 % and 41 % were observed foruntreated samples stored using the room temperature, +4, −20 ∘C, and flash-frozen protocols, respectively.Finally, the estimated uncertainties associated with the four storage protocolsare provided for untreated, heat-treated and filtered samples for INPsbetween −9 and −17 ∘C.more » « less
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/acp-21-14725-2021
