In situ detection of the chemistry of individual fog droplet residues in the Pearl River Delta region, China

Abstract

We use a single‐particle aerosol mass spectrometer coupled with a ground‐based counterflow virtual impactor to measure the chemical compositions of individual submicron fog droplet residues. This is the first report on single particle mass spectrometry measurements of fog droplet residual particles at ground level in an urban area. We show that most of the fog droplet residues were composed of elemental carbon (EC) (67.7%), followed by K‐rich (19.2%) and mineral dust/metal (12.3%) particles. The predominance of EC‐containing particles demonstrated that these particles could be effective fog nuclei and highlights the important influence of anthropogenic emissions on regional climate system. Compared with interstitial and ambient aerosols, nitrate was enhanced, sulfate was depressed, and ammonium‐ and organics‐containing particles were hardly found in the fog droplet residues during fog events, suggesting that dust and metal particles containing nitrate may be preferentially activated and that ammonium and organics may not play important roles in fog formation in Guangzhou. We also present direct observational evidence that trimethylamine and hydroxymethanesulfonate are not found within fog droplet residues, although we previously observed enhanced gas‐to‐particle partitioning of these compounds by fog processing. Additionally, higher fraction or intensities of [K]+, [Fe]+, and [SiO3]− were found in fog droplet residues than in ambient and interstitial particles.

In situ chemical composition measurement of individual cloud residue particles at a mountain site, southern China

“…The contribution of local anthropogenic origins to aged soot and/or biomass-burning parti-cles in cloud or fog residues has been reported in Schmücke (Roth et al, 2016) and Guangzhou city (Bi et al, 2016). At the North Slope of Alaska, the measurement of biomassburning particles in cloud residues mainly resulted from the local vicinity, or sources as far away as Siberia and Asia (Zelenyuk et al, 2010;Hiranuma et al, 2013).…”

“…The same experimental methods of Bi et al (2016) were used in this study. The size distribution, chemical composition and mixing state of cloud residues during cloud events are discussed.…”

“…This result showed that sulfate-related salts dominated in larger particles. Bi et al (2016) used a groundcounterflow virtual impactor (GCVI) coupled with a realtime single-particle aerosol mass spectrometer (SPAMS) to explore the chemical composition and mixing state of individual fog residual particles at ground level in an urban area of southern China. They found an abundance of ECcontaining particles in fog residues.…”

“…A rainfall detector of the GCVI system was also used to exclude rain droplet contamination. When cloud events occurred without precipitation, sampling was automatically triggered by the GCVI control software (Bi et al, 2016). (72 h) for air masses at 1800 m during the whole sampling period.…”

“…To reliably identify the presence of cloud events, an upperlimit visibility threshold of 5 km and a lower-limit RH threshold of 95 % were set in the GCVI software (Bi et al, 2016). Three long-lasting cloud events occurred during the periods of 16:00 LT 15 January to 07:00 LT 17 January (cloud I), 20:00 LT 18 January to 12:00 LT 19 January (cloud II) and 17:00 LT 19 January to 13:00 LT 23 January (cloud III), as marked in Fig.…”