Abstract. Biogenic organic precursors play an important role inatmospheric new particle formation (NPF). One of the major precursor speciesis α-pinene, which upon oxidation can form a suite of productscovering a wide range of volatilities. Highly oxygenated organic molecules(HOMs) comprise a fraction of the oxidation products formed. While it isknown that HOMs contribute to secondary organic aerosol (SOA) formation,including NPF, they have not been well studied in newly formed particles dueto their very low mass concentrations. Here we present gas- and particle-phase chemical composition data from experimental studies of α-pinene oxidation, including in the presence of isoprene, at temperatures(−50 and −30 ∘C) and relativehumidities (20 % and 60 %) relevant in the upper free troposphere. Themeasurements took place at the CERN Cosmics Leaving Outdoor Droplets (CLOUD)chamber. The particle chemical composition was analyzed by a thermaldesorption differential mobility analyzer (TD-DMA) coupled to a nitratechemical ionization–atmospheric pressure interface–time-of-flight(CI-APi-TOF) mass spectrometer. CI-APi-TOF was used for particle- and gas-phase measurements, applying the same ionization and detection scheme. Ourmeasurements revealed the presence of C8−10 monomers and C18−20dimers as the major compounds in the particles (diameter up to∼ 100 nm). Particularly, for the system with isoprene added,C5 (C5H10O5−7) and C15 compounds(C15H24O5−10) were detected. This observation is consistentwith the previously observed formation of such compounds in the gas phase. However, although the C5 and C15 compounds do not easily nucleate,our measurements indicate that they can still contribute to the particlegrowth at free tropospheric conditions. For the experiments reported here,most likely isoprene oxidation products enhance the growth of particleslarger than 15 nm. Additionally, we report on the nucleation rates measuredat 1.7 nm (J1.7 nm) and compared with previous studies, we found lowerJ1.7 nm values, very likely due to the higher α-pinene andozone mixing ratios used in the present study.
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Temperature effects on sulfuric acid aerosol nucleation and growth: initial results from the TANGENT study
Abstract. New particle formation (NPF) consists of two steps: nucleation andsubsequent growth. At present, chemical and physical mechanisms that governthese two processes are not well understood. Here, we report initial resultsobtained from the TANGENT (Tandem Aerosol Nucleation and Growth EnvironmentTube) experiments. The TANGENT apparatus enables us to study these twoprocesses independently. The present study focuses on the effects oftemperature on sulfuric acid nucleation and further growth. Our results showthat lower temperatures enhance both the nucleation and growth rate.However, under temperatures below 268 K the effects of temperature on thenucleation rate become less significant and the nucleation rate becomes lessdependent on relative humidity, indicating that particle formation in the conditions of ourflow tube takes place via barrierless nucleation at lower temperatures. Wealso examined the growth of newly formed particles under differingtemperature conditions for nucleation and further growth. Our results showthat newly nucleated clusters formed at low temperatures can indeed surviveevaporation and grow in a warmer environment in the presence of SO2 andozone and potentially other contaminant vapors. These results implythat some heterogeneous reactions involving nanoparticles affect nucleationand growth of newly formed particles.
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- NSF-PAR ID:
- 10137143
- Date Published:
- Journal Name:
- Atmospheric Chemistry and Physics
- Volume:
- 19
- Issue:
- 13
- ISSN:
- 1680-7324
- Page Range / eLocation ID:
- 8915 to 8929
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/acp-19-8915-2019
