Fast particulate nitrate formation via N<sub>2</sub>O<sub>5</sub> uptake aloft in winter in Beijing

Abstract

Abstract. Particulate nitrate (pNO − 3 ) is an important component of secondary aerosols in urban areas. Therefore, it is critical to explore its formation mechanism to assist with the planning of haze abatement strategies. Here we report vertical measurements of NO x and O 3 by in situ instruments on a movable carriage on a tower during a winter heavy-haze episode (18 to 20 December 2016) in urban Beijing, China. Based on the box model simulation at different heights, we found that pNO − 3 formation via N 2 O 5 heterogeneous uptake was negligible at ground level due to N 2 O 5 concentrations of near zero controlled by high NO emissions and NO concentration. In contrast, the contribution from N 2 O 5 uptake was large at high altitudes (e.g., > 150 m), which was supported by the lower total oxidant (NO 2 + O 3 ) level at high altitudes than at ground level. Modeling results show the specific case that the nighttime integrated production of pNO − 3 for the high-altitude air mass above urban Beijing was estimated to be 50 µg m −3 and enhanced the surface-layer pNO − 3 the next morning by 28 µg m −3 through vertical mixing. Sensitivity tests suggested that the nocturnal NO x loss by NO 3 -N 2 O 5 chemistry was maximized once the N 2 O 5 uptake coefficient was over 2 × 10 −3 on polluted days with S a at 3000 µm 2 cm −3 in wintertime. The case study provided a chance to highlight the fact that pNO − 3 formation via N 2 O 5 heterogeneous hydrolysis may be an important source of particulate nitrate in the urban airshed during wintertime.

Vertical Characterization of Aerosol Particle Composition in Beijing, China: Insights From 3‐Month Measurements With Two Aerosol Mass Spectrometers

“…The vertical evolutions of aerosol species were much different among severe haze episodes. As shown in Figure , nitrate showed overall higher ratios 260m/ground than other inorganic species during all haze episodes due to the higher formation potential from gas‐particle partitioning (Sun, Du, et al, ) and nighttime heterogeneous reactions at higher altitudes (Wang, Lu, et al, ). The vertical differences in OA factors were more different between POA and SOA factors.…”

“…An explanation for the higher nitrate at 260 m was the lower T that facilitated gas‐particle partitioning (Figure S3). Another reason was the higher nitrate production via heterogeneous reactions of N 2 O 5 at higher heights due to high O 3 and low NO (Wang, Lu, et al, ). Despite all NR‐PM 1 species being consistently higher at ground level than 260 m during HP2, the compositions of NR‐PM 1 were generally similar between the two heights, which mainly comprised of organics (52%–54%), sulfate (14%–16%), and nitrate (14%–15%).…”

Interaction Between Planetary Boundary Layer and PM2.5 Pollution in Megacities in China: a Review

“…For instance, due to the more cooling condition aloft that favors the gas-particle partitioning, the mass fraction and concentration of particulate nitrate were reported higher aloft (e.g., 260 m) than at the ground level in Beijing [29]. The nighttime integrated production of particulate nitrate in the residual layer above can significantly increase the near-surface aerosol concentration in the next morning through vertical mixing [71].…”

Characterization of submicron particles by Time-of-Flight Aerosol Chemical Speciation Monitor (ToF-ACSM) during wintertime: aerosol composition, sources and chemical processes in Guangzhou, China

“…Photochemistry which highly depends on daytime solar radiation is commonly believed to play a dominant role in formation of secondary PM (SPM = ammonium + nitrate + sulfate + OOA); However, recent studies showed that the contribution from aqueous reactions or heterogeneous reactions cannot be ignored. For instances, it has been found that the heterogeneous hydrolysis of N2O5 on the surface of deliquescent aerosols is a 135 significant pathway for nitrate formation during nighttime (Wang et al, 2018;Wen et al, 2018). proposed that the mass concentration of sulfate substantially increased through fog processes.…”