Effects of continental emissions on cloud condensation nuclei (CCN) activity in the northern South China Sea during summertime 2018

Abstract

Abstract. Aerosol particles in marine atmosphere have been shown to significantly affect cloud formation, atmospheric optical properties, and climate change. However, high temporally and spatially resolved atmospheric measurements over the sea are currently sparse, limiting our understanding of aerosol properties in marine atmosphere. In this study, a ship-based cruise campaign was conducted over the northern South China Sea (SCS) region during summertime 2018. The chemical composition of non-refractory PM1 (NR-PM1), the particle number size distribution (PNSD), and size-resolved cloud condensation nuclei (CCN) activity were measured by a time-of-flight aerosol chemical speciation monitor (ToF-ACSM) and the combination of a cloud condensation nuclei counter (CCNc) and a scanning mobility particle sizer (SMPS). Overall, aerosol particles exhibited a unimodal distribution centering at 60–80 nm and the chemical composition of the NR-PM1 was dominated by sulfate (∼ 46 %), which likely originated from anthropogenic emissions rather than dimethyl sulfide (DMS) oxidation. Two polluted episodes (P1 and P2) were observed, and both were characterized by high particle number concentrations (NCN) which originated from local emissions and from emissions in inland China via long-range transport. The concentrations of trace gases (i.e., O3, CO, NOx) and particles (NCN and NCCN at ss = 0.34 %) were elevated during P2 at the end of the campaign and decreased with offshore distance, further suggesting important impacts of anthropogenic emissions from the inland Pearl River Delta (PRD) region. Two relatively clean periods (C1 and C2) prior to and after tropical storm Bebinca were classified and the air was affected by air masses from the southwest and from the Indo-Chinese Peninsula, respectively. Chemical composition measurements showed an increase in organic mass fraction during P2 compared to C2; however, no obviously different κ values were obtained from the CCNc measurements, implying that the air masses carried pollutants from local sources during long-range transport. We report an average value of about 0.4 for the aerosol hygroscopicity parameter κ, which falls within the literature values (i.e., 0.2–1.0) for urban and remote marine atmosphere. In addition, our results showed that the CCN fraction (NCCN∕NCN, tot) and the κ values had no clear correlation either with the offshore distance or with concentrations of the particles. Our study highlights dynamical variations in particle properties and the impact of long-range transport from continental China and the Indo-Chinese Peninsula on the northern SCS region during summertime.

Contribution of New Particle Formation to Cloud Condensation Nuclei Activity and its Controlling Factors in a Mountain Region of Inland China

“…In Thüringer Mountain (Germany), both high and low values of hygroscopicity (a hygroscopic growth factor of around 1.4-1.55 and 1.2-1.35, respectively) were reported for particles with a size range of 25-45 nm during NPF events (Wu et al, 2013). An average value of about 0.4 for the aerosol hygroscopicity parameter was recently reported in northern South China Sea region, indicating influence of continental emissions on CCN activity (M. Cai et al, 2020). Hence, the mechanism of nucleation and growth of nanoparticles can be different under different environments depending on participant species in the processes and currently large uncertainties on the N CCN prediction exist from measurements of NPF events.…”

Evaluation of the contribution of new particle formation to cloud droplet number concentration in the urban atmosphere

“…The number size distribution of particles in the size range from 10 to 550 nm (scanned range) was measured with a time resolution of 5 min by a scanning mobility particle sizer (SMPS; Wang and Flagan, 1990;Collins et al, 2002), which consists of a differential mobility analyzer (DMA, model 3081L, TSI Inc.) to classify particles with different sizes of particles, and a condensation particle counter (CPC, model 3772, TSI Inc.) to detect the size-classified particles. The sampled particles were dried to a relative humidity < 30 % before entering the DMA.…”

The important roles of surface tension and growth rate in the contribution of new particle formation (NPF) to cloud condensation nuclei (CCN) number concentration: evidence from field measurements in southern China

“…( 9). The formation rate (J k ) described the flux through a certain diameter (k) during NPF events, and it is calculated based on the formula given in Cai and Jiang (2017),…”