A proxy for atmospheric daytime gaseous sulfuric acid concentration in urban Beijing

Abstract

Abstract. Gaseous sulfuric acid (H2SO4) is known as one of the key precursors for atmospheric new particle formation (NPF) processes, but its measurement remains challenging. Therefore, a proxy method that is able to derive gaseous sulfuric acid concentrations from parameters that can be measured relatively easily and accurately is highly desirable for the atmospheric chemistry community. Although such methods are available for clean atmospheric environments, a proxy that works well in a polluted atmosphere, such as that found in Chinese megacities, is yet to be developed. In this study, the gaseous sulfuric acid concentration was measured in February–March 2018, in urban Beijing using a nitrate based – long time-of-flight chemical ionization mass spectrometer (LToF-CIMS). A number of atmospheric parameters were recorded concurrently including the ultraviolet radiation B (UVB) intensity, the concentrations of O3, NOx (sum of NO and NO2), SO2, and HONO, and aerosol particle number size distributions. A proxy for atmospheric daytime gaseous sulfuric acid concentration was derived via a statistical analysis method using the UVB intensity, [SO2], the condensation sink (CS), [O3], and [HONO] (or [NOx]) as the predictor variables, where square brackets denote the concentrations of the corresponding species. In this proxy method, we considered the formation of gaseous sulfuric acid from reactions of SO2 and OH radicals during the daytime, and the loss of gaseous sulfuric acid due to its condensation onto the preexisting particles. In addition, we explored the formation of OH radicals from the conventional gas-phase photochemistry using O3 as a proxy and from the photolysis of HONO using HONO (and subsequently NOx) as a proxy. Our results showed that the UVB intensity and [SO2] are dominant factors in the production of gaseous sulfuric acid, and that the simplest proxy could be constructed with the UVB intensity and [SO2] alone. When the OH radical production from both homogenously and heterogeneously formed precursors were considered, the relative errors were reduced by up to 20 %.

Variation of size-segregated particle number concentrations in wintertime Beijing

“…High concentrations of SO 2 have been ascribed to regional pollution and an anthropogenic condensation sink even in semipristine environments (Dada et al, 2017). Earlier observations report that the main sources of SO 2 are power plants, traffic and industry, so SO 2 can be used as a tracer for regional pollution Lu et al, 2010). Generally, as shown in Fig.…”

Sources and sinks driving sulfuric acid concentrations in contrasting environments: implications on proxy calculations

“…Sulfuric acid (H 2 SO 4 ), which has a very low saturation vapor pressure and strong hydrogen bonding capability (Zhang et al, 2011), has been found to be the major precursor of atmospheric NPF (Weber et al, 1996;Kulmala et al, 2004;Sihto et al, 2006;Sipilä et al, 2010;Erupe et al, 2011;Lehtipalo et al, 2018;Ma et al, 2019) and is often used in global models for simulating the occurrence and intensity of new particle formation events (Dunne et al, 2016). However, atmospheric measurements of gas-phase sulfuric acid are rare, mainly due to its low concentration (10 6 -10 7 molecules cm −3 or below) that can only be measured using state-of-the-art instruments (Mikkonen et al, 2011), such as the chemical ionization atmospheric-pressure interface time-of-flight spectrometer (CI-APi-ToF) (Eisele and Tanner, 1993;Jokinen et al, 2012).…”

Investigating three patterns of new particles growing to the size of cloud condensation nuclei in Beijing's urban atmosphere

“…Class III can be further classified into three growth patterns, which will be detailed in later sections. In addition to particle size, various factors such as chemical composition, particle mixing states, and meteorological conditions may also largely affect CCN activation of aerosols with D pg beyond 70 nm (Ma et al, 2016;Rose et al, 2017;Lee et al, 2019). Although new particles in class III can grow to CCN size, the CCN activation of grown new particles has been reported to vary case by case (Wiedensohler et al, 2009;Yue et al, 2011;Li et al, 2015;Ma et al, 2016).…”

“…Modeling studies have also proposed that approximately 50 % of the CCN population is attributable to NPF events in the troposphere (Yu and Luo, 2009;Yu et al, 2014;Gordon et al, 2017). Nevertheless, reported observations have also shown that newly formed particles with diameters less than 40-50 nm can be activated as CCN only under high supersaturation (SS), such as > 0.6 % (Li et al, 2015;Ma et al, 2016). When newly formed particles grow to a geometric median diameter of larger than 70 nm, they significantly contribute to the CCN population at SS ≤ 0.2 % (Wiedensohler et al, 2009;Yue et al, 2011;Li et al, 2015;Ma et al, 2016;Zhu et al, 2019).…”

“…Nevertheless, reported observations have also shown that newly formed particles with diameters less than 40-50 nm can be activated as CCN only under high supersaturation (SS), such as > 0.6 % (Li et al, 2015;Ma et al, 2016). When newly formed particles grow to a geometric median diameter of larger than 70 nm, they significantly contribute to the CCN population at SS ≤ 0.2 % (Wiedensohler et al, 2009;Yue et al, 2011;Li et al, 2015;Ma et al, 2016;Zhu et al, 2019). In addition, field observations have also shown that in most NPF events, the maximum geometric median diameter (D pgmax ) of newly grown particles is less than 40-50 nm before new particle signals drop to a negligible level (Zhu et al, 2014(Zhu et al, , 2017Man et al, 2015;Yu et al, 2019).…”