Evaluating measurements of new particle concentrations, source rates, and spatial scales during coastal nucleation events using condensation particle counters

Abstract

Condensation particle counters (CPCs), used to examine particle production in the coastal environment, are evaluated for their ability to differentiate ultrafine sizes between 3 and 10 nm, along with their ability to count high total particle number concentrations encountered during coastal nucleation events. Four ultrafine particles counters, with a 3 nm detection limit, were deployed in a spatial array comprising a triangular distribution with nodes approximately 100 m apart (two at 3 m height, one at 10 m). A fourth node was deployed at 20 m. The 10 m and 20 m node comprised additional CPCs with detection limits of 5 and 10 nm. Size cutoff efficiency calibrations were performed in the field, and all CPCs were found to be within the manufacturer's specifications. During the nucleation events it was found that peak particle concentrations of the order of 180,000 cm−3 were encountered, and as a result, coincidence calibrations were also performed in the laboratory. It was found that, at concentrations over 100,000 cm−3, the CPCs significantly underestimated the true concentrations by a factor of about 5–6. Total particle concentrations were also measured using a 30‐times dilution system and an ultrafine CPC, along with integrated total concentration derived from the ultrafine Differential Mobility Particle Sizer (DMPS). Comparison of laboratory‐derived corrections for coincidence and both the diluted CPC total concentrations and DMPS concentrations revealed very good agreement and confirmed that peak particle concentrations during coastal nucleation bursts result in new particle concentrations as high as 1.2 × 106 cm−3. The DMPS total concentration was somewhat lower than the diluted CPC concentration, suggesting that the recommended method of measuring such high concentrations is to dilute the sample significantly. The lower concentrations from the DMPS are partially due to the 10 min integration time being insufficient to resolve peaks seen by the CPC operated at 1 Hz. Taking the corrected concentrations in account, 3 nm particle source rates were calculated to be >105 cm−3 s−1. The spatial array of CPCs revealed that within the general coastal nucleation plume, there are numerous microplumes with spatial scales of the order of 10–100 m when sampling is conducted near the source region. Further from the source region these microplumes merge into the general coastal plume.