Insight into winter haze formation mechanisms based on aerosol hygroscopicity and effective density measurements

Abstract

Abstract. We characterize a representative particulate matter (PM) episode that occurred in Shanghai during winter 2014. Particle size distribution, hygroscopicity, effective density, and single particle mass spectrometry were determined online, along with offline analysis of water-soluble inorganic ions. The mass ratio of SNA / PM 1.0 (sulfate, nitrate, and ammonium) fluctuated slightly around 0.28, suggesting that both secondary inorganic compounds and carbonaceous aerosols contributed substantially to the haze formation, regardless of pollution level. Nitrate was the most abundant ionic species during hazy periods, indicating that NO x contributed more to haze formation in Shanghai than did SO 2 . During the representative PM episode, the calculated PM was always consistent with the measured PM 1.0 , indicating that the enhanced pollution level was attributable to the elevated number of larger particles. The number fraction of the near-hydrophobic group increased as the PM episode developed, indicating the accumulation of local emissions. Three "banana-shaped" particle evolutions were consistent with the rapid increase of PM 1.0 mass loading, indicating that the rapid size growth by the condensation of condensable materials was responsible for the severe haze formation. Both hygroscopicity and effective density of the particles increased considerably with growing particle size during the bananashaped evolutions, indicating that the secondary transformation of NO x and SO 2 was one of the most important contributors to the particle growth. Our results suggest that the accumulation of gas-phase and particulate pollutants under stagnant meteorological conditions and subsequent rapid particle growth by secondary processes were primarily responsible for the haze pollution in Shanghai during wintertime.

Distinct Ultrafine‐ and Accumulation‐Mode Particle Properties in Clean and Polluted Urban Environments

“…The H‐TDMA can measure the GF probability distribution function (GF‐PDF) for particles with a specified diameter. Detailed information on the aerosol hygroscopicity conveyed in the measurements of the H‐TDMA can be used to study aerosol sources (Y. Wang et al, ; Xie et al, ). This is because the GF‐PDF pattern depends on aerosol chemical composition and the mixing state, both of which are highly related to aerosol formation and aging processes (Liu et al, ; Wang et al, ).…”

“…LH‐ and MH‐mode particles thus represent different aerosol sources and chemical processes. Implied aerosol chemical information from the GF‐PDF/ κ ‐PDF can be used to analyze particle formation processes for particles of different sizes, which is necessary to study the haze formation mechanism (X. Wang et al, ; Xie et al, ).…”

“…Implied aerosol chemical information from the GF-PDF/κ-PDF can be used to analyze particle formation processes for particles of different sizes, which is necessary to study the haze formation mechanism (X. Xie et al, 2017).…”

Non-polar organic compounds in autumn and winter aerosols in a typical city of eastern China: size distribution and impact of gas–particle partitioning on PM<sub>2.5</sub> source apportionment

“…China has experienced numerous severe and long-lasting haze episodes since winter in 2013, which has affected over 600 million local residents and covered a quarter of the country's land area (Huang et al, 2014;Hao and Liu, 2015). In essence, a haze episode is caused by the distribution of particulate matter with different sizes in atmosphere, leading to a decrease in visibility (Xie et al, 2017). Carbonaceous aerosols contain a large amount of particulate matter, accounting for 30-50 % of PM 2.5 mass concentrations (Yadav et al, 2013;Wang et al, 2016;Ma et al, 2018).…”

“…Because non-polar organic compounds (NPOCs) can provide specific information on the identification of aerosol sources, they are now of special interest to researchers (Rajput and Sarin, 2014;Wang et al, 2016). n-Alkanes, polycyclic aromatic hydrocarbons (PAHs), hopanes and steranes are four typical NPOC species and are frequently used to apportion sources of ambient particulate matter (Xu et al, 2013;Zhao et al, 2016). n-Alkanes are emitted from natural and anthropogenic activities, including particulate abrasion products from leaf surfaces of vegetation and fossil fuel combustion.…”