Aerosol high water contents favor sulfate and secondary organic aerosol formation from fossil fuel combustion emissions

Abstract

Fine-particle pollution associated with high sulfate and secondary organic aerosol (SOA) contents still occurs in winter, despite considerable reductions in precursor emissions in China. The chemical mechanisms involved are consistently acknowledged to be linked with aerosol water but remain poorly understood. Here, we present findings demonstrating that the synergistic effect of elevated aerosol water content and particles originating from fossil fuel combustion significantly enhanced the rapid formation of sulfate and SOAs under high humidity conditions during winter in northern China. The presence of high aerosol water content promoted the aging process of particles containing elemental carbon (EC) and facilitated the formation of SOAs. Evidence from single particles reveals an increased potential for SOA formation from primary organic aerosols (POAs) originating from fossil fuel combustion, in the presence of increasing aerosol water. Under conditions of relative humidity exceeding 85%, the multiphase oxidation of SO2 by in-particle nitrite/nitrous acid, generated through reactions involving aged EC-containing and iron-rich particles, as well as aqueous-phase formation of hydroxymethanesulfonate (HMS), led to a substantial increase in sulfate production. This study emphasizes the critical role of aerosol water in the aerosol chemistry concerning sulfate and SOAs, highlighting the urgent necessity to mitigate primary emissions from fossil fuel combustion.

Relaxation of Spring Festival Firework Regulations Leads to a Deterioration in Air Quality

“…The number fraction of particles containing a specific ion in total particles was obtained through a conventional ion search procedure with COCO v1.4 software. The particle size detected by SPAMS was not scaled by a scanning mobility particle sizer for potential deviations caused by size-dependent particle transmission of the aerodynamic lens employed in SPAMS; − nevertheless, it still captured the underlying trend of particle size evolution. ,, …”

“…Subsequently, we manually identified and classified the particle types into six primary groups, comprising a total of 21 subtypes (Figures S1−S3) based on the combined signatures of dominant marker ions in both positive and negative mass spectra together with the particle sizes. 29 The abundance of sulfate was quantified by determining the combined sum of the relative peak area (RPA) for m/z −80 and −97 across all the particles; nitrate, by the RPA for m/z −62 and −46; ammonium, by the RPA of m/z +18; and chloride (Cl), by the RPA for m/z −35 and −37. The number fraction of particles containing a specific ion in total particles was obtained through a conventional ion search procedure with COCO v1.4 software.…”

“…The particle size detected by SPAMS was not scaled by a scanning mobility particle sizer for potential deviations caused by size-dependent particle transmission of the aerodynamic lens employed in SPAMS; 30−32 nevertheless, it still captured the underlying trend of particle size evolution. 29,33,34 WRF-CMAQ Model Simulation and Quantification of Meteorological Contribution. The weather research and forecasting (WRF v3.7) and community multiscale air quality (CMAQ v5.0.2) models were employed to simulate the air quality during the SFs of 2022 and 2023, under the corresponding meteorological conditions without considering fireworks (termed the base case).…”

“…ECsul, bareEC, and NaKECCN particles were freshly emitted from fireworks, as indicated by their low intensity of nitrate. 29 KOC particles displayed noticeable OC peaks at m/z +27, +37, +43, +50, +51, +61 ∼ 63, +74, and +77 and strong peaks corresponding to nitrate and sulfate. The abundance of this particle type increased rapidly during firework displays, reaching 11.0% at 01:00 on NYE and 12.9% at 21:00 on LF (Figure S3), contributing 7.5%, on average, to the total particles.…”

“…After being released from fireworks, the particles exhibited a broader size distribution over time (Figure S10a). Fresh particles, with a lower intensity of nitrate in the mass spectrum, 29 constituted 40% of the total single particles during high-intensity fireworks (FW, from 20:00 to 2:00 on NYE, NYDN and LFN) (Figure 4a). This proportion decreased to 35% during postfirework hours (post-FW, from 3:00 to 13:00 following the fireworks) and further declined to 25% during pollution after LF (from 14:00 on Feb. 6 to 17:00 on Feb. 8).…”