A point-by-point response to the reviews

We characterize a representative haze event from a series of periodic particulate matter (PM) episodes that occurred in Shanghai during winter 2014. Particle size distribution, hygroscopicity, effective density and effective density single particle mass spectrometry were measured determined online, along with offline analysis of water-soluble inorganic ions and single particle mass spectrometry. Regardless of pollution level, Tthe mass ratio of SNA/PM1.0 (sulfate, nitrate, and ammonium) slightly fluctuated slightly around 0.28, over the whole observation, suggesting that both secondary inorganic compounds and carbonaceous aerosols (including soot and organic matter) contributed substantially to the haze formation, 19 regardless of pollution level. . Nitrate was the most abundant ionic species during hazy periods, indicating that NOx contributed more to haze formation in Shanghai than did SO2. During the representative PM episode, Tthe calculated PM concentration from particle size distribution displayed a variation pattern similar to that of was always consistent with the measured PM1.0, during the representative PM episode, 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 in PM1.0 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 banana-shaped evolutions, indicating that the secondary transformation of NOx and SO2 was one of the most importanta major 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.