Variations of cloud condensation nuclei (CCN) and aerosol activity during fog–haze episode: a case study from Shanghai

Abstract

Abstract. Measurements of cloud condensation nuclei (CCN), condensation nuclei (CN) and aerosol chemical composition were performed simultaneously at an urban site in Shanghai from 6 to 9 November 2010. The variations of CCN number concentration (N CCN ) and aerosol activity (activated aerosol fraction, N CCN /N CN ) were examined during a fog-haze co-occurring event. Anthropogenic pollutants emitted from vehicles and unfavorable meteorological conditions such as low planetary boundary layer (PBL) height exerted a great influence on PM 2.5 and black carbon (BC) loadings. N CCN at 0.2 % supersaturation (SS) mostly fell in the range of 994 to 6268 cm −3 , and the corresponding N CCN /N CN varied between 0.09 and 0.57. N CCN and N CCN /N CN usually were usually higher in the hazy case due to increased aerosol concentration in the accumulation mode (100-500 nm), and lower in the foggy-hazy and clear cases. The BC mass concentration posed a strong positive effect on N CCN in the foggy-hazy and hazy cases, whereas it poorly correlated with N CCN in the clear case. N CCN /N CN was weakly related with BC in both foggy-hazy and hazy cases. By using a simplified particle hygroscopicity (κ), the calculated critical dry size (CDS) of activated aerosol did not exceed 130 nm at 0.2 % SS in spite of diverse aerosol chemical compositions. The predicted N CCN at 0.2 % SS was very successful compared with the observed N CCN in clear case (R 2 = 0.96) and foggy-hazy/hazy cases (R 2 = 0.91). In addition, their corresponding ratios of predicted to observed N CCN were on average 0.95 and 0.92, respectively. More organic matter is possibly responsible for this closure difference between foggy-hazy/hazy and clear cases. These results reveal that the particulate pollutant burden exerts a significant impact on N CCN , especially N CCN /N CN promotes effectively during the polluted periods.

Insights into a historic severe haze event in Shanghai: synoptic situation, boundary layer and pollutants

“…It tends to reduce cloud droplet size and then suppress the wet precipitation in shallow and shortlived clouds (Lohmann and Feichter, 2005). Previous studies in Shanghai have found that CCN number concentration (N CCN ) and aerosol activity promotes effectively during the polluted periods (Leng et al, 2013(Leng et al, , 2014a. In north India, Ritesh et al (2007) observed a significant impact of winter haze on N CCN .…”

“…When 80 % < RH < 90 %, the event is referred to as a complex of haze-fog co-occurring or transition (Leng et al, 2014a), and it is also classified as hazy episode in the present study. Figure 1a depicts the temporal variations of hourly PM 2.5 , PM 10 , atmospheric visibility and meteorological factors from 1 to 10 December 2013.…”

“…The instrument has been calibrated for SS using standard (NH 4 ) 2 SO 4 particles every 3 months since 2010. According to the instrument operation manual, regular calibrations were also performed for temperature gradient, input and shear airflows and pressure to maintain stable SS (Leng et al, 2013(Leng et al, , 2014a. Periodic zero checks were done to ensure counting accuracy for optical particle counter (OPC) inside the CCN counter.…”

Measurements of PM10 ions and trace gases with the online system MARGA at the research station Melpitz in Germany – A five-year study

“…Observations of linearity between sulphate and nitrate in PM (2009 to 2011) Leng et al (2014a) Shanghai, CN Role of new particle formation on aerosol cloud condensation nuclei (CCN) activity (2012) Leng et al (2014b) Shanghai, CN Variations of CCN and aerosol activity during fog and haze events (2010) Makkonen et al (2014) Hyytiälä, FI Temporal cycles of NH 3 , HONO and HNO 3 at a boreal forest site (2010 to 2011) Rumsey et al (2014) North Carolina, US Performance study of the MARGA (US Environmental Protection Agency's Clean Air Status and Trends Network, CASTnet) (2010) Shi et al (2014) Shanghai, CN Investigation on PM 1 (variability, formation/dissociation, impacts on visibility) (2012) Zhou et al (2014) Shanghai, CN Measuring and modelling aerosols for haze events (2008 to 2010) a net radiometer CNR1 (Kipp&Zonen, The Netherlands) and a digital barometer (Vaisala, Germany), respectively.…”

Long‐Term Fog Variation and Its Impact Factors Over Polluted Regions of East China

“…Some studies (Ding & Liu, ; F. Niu, Li, et al, ) investigated the relations between fog and haze or aerosols but did not study the role of aerosols as cloud condensation nuclei. Therefore, we analyze fog‐aerosol relationships from the perspective of aerosol‐cloud interactions because fog can be viewed as near‐surface clouds (Leng et al, ; Zhu & Guo, ). This analysis can help to reveal how anthropogenic activities influence cloud physics.…”