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Abstract Ice‐nucleating particles (INPs) play a key role in ice formation and cloud microphysics and thus significantly impact the water cycle and the climate. However, our understanding of atmospheric INPs, particularly their sources, emissions, and spatiotemporal variability, is incomplete. While the enhancement of atmospheric INP concentrations with rainfall has been previously shown, a mechanistic understanding of the process is lacking. Here, we link detailed precipitation observations with near‐surface atmospheric INP concentrations at a semiarid grassland site in Colorado. Considering the during‐precipitation air samples, INP concentrations positively correlate with cumulative rainfall kinetic energy and amount, suggesting that INP aerosolization is induced by raindrop and hailstone impact. By additionally analyzing the INP content of precipitation water, terrestrial source samples, and heat‐treated samples, we demonstrate that local plants are the most plausible source of rain‐induced INPs during a precipitation event. Should INPs aerosolized by precipitation rise to cloud height, they could influence cloud ice fraction and initiate precipitation resulting in an aerosol‐cloud‐precipitation feedback.
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Best practices for precipitation sample storage for offline studies of ice nucleation in marine and coastal environments
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.
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- Award ID(s):
- 1801971
- PAR ID:
- 10232158
- Date Published:
- Journal Name:
- Atmospheric Measurement Techniques
- Volume:
- 13
- Issue:
- 12
- ISSN:
- 1867-8548
- Page Range / eLocation ID:
- 6473 to 6486
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/amt-13-6473-2020
