Abstract
Abstract. Atmospheric new-particle formation (NPF) is a worldwide-observed phenomenon that affects the human health and the global climate. With a growing network of global atmospheric measurement stations, efforts towards investigating NPF have increased. In this study, we present an automated method to classify days into four categories including NPF events, non-events and two classes in between, which then ensures reproducibility and minimizes the hours spent on manual classification. We applied our automated method to 10 years of data collected at the SMEAR II measurement station in Hyytiälä, southern Finland using a Neutral cluster and Air Ion Spectrometer (NAIS). In contrast to the traditionally applied classification methods, which categorize days into events and non-events and ambiguous days as undefined days, our method is able to classify the undefined days as it accesses the initial steps of NPF at sub-3 nm sizes. Our results show that, on ∼24 % of the days in Hyytiälä, a regional NPF event occurred and was characterized by nice weather and favourable conditions such as a clear sky and low condensation sink. Another class found in Hyytiälä is the transported event class, which seems to be NPF carried horizontally or vertically to our measurement location and it occurred on 17 % of the total studied days. Additionally, we found that an ion burst, wherein the ions apparently fail to grow to larger sizes, occurred on 18 % of the days in Hyytiälä. The transported events and ion bursts were characterized by less favourable ambient conditions than regional NPF events and thus experienced interrupted particle formation or growth. Non-events occurred on 41 % of the days and were characterized by complete cloud cover and high relative humidity. Moreover, for regional NPF events occurring at the measurement site, the method identifies the start time, peak time and end time, which helps us focus on variables within an exact time window to better understand NPF at a process level. Our automated method can be modified to work in other measurement locations where NPF is observed.
Highlights
New-particle formation (NPF) is an atmospheric phenomenon that results in a big addition to aerosol load in the global troposphere (Spracklen et al, 2010; Kerminen et al, 2018)
REs, or regional new-particle formation (NPF) events, are those which are initiated over a large area, including the measurement location, and the particles continue to grow to bigger sizes
The type IB, or ion bursts, is an attempt at NPF, during which clusters form in Hyytiälä; they do not grow beyond www.atmos-chem-phys.net/18/17883/2018/
Summary
New-particle formation (NPF) is an atmospheric phenomenon that results in a big addition to aerosol load in the global troposphere (Spracklen et al, 2010; Kerminen et al, 2018). With a growing number of global stations (Kulmala, 2018), an automatic method is needed to classify the days into events and non-events. We present an automated method which classifies days into four classes according to the observed characteristics of 2–4 nm sized air ions and 7–25 nm sized particles. The original classification method of days as events, non-events and undefined days was proposed by Dal Maso et al (2005), later modified by Kulmala et al (2012) and is based on particle measurements starting from about 3 nm in particle mobility diameter, missing the initial steps of NPF. Our automated method identifies the start, peak and end times of daytime regional events or ion bursts. By identifying the start and end times, we are able to concentrate on the conditions present during the actual NPF time window
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