Enhanced Nitrate Fraction: Enabling Urban Aerosol Particles to Remain in a Liquid State at Reduced Relative Humidity

Y. C. Liu; Z. J. Wu; Y. T. Qiu; P. Tian; Q. Liu; Y. Chen; M. Song; M. Hu

doi:10.1029/2023gl105505

Enhanced Nitrate Fraction: Enabling Urban Aerosol Particles to Remain in a Liquid State at Reduced Relative Humidity

Y. C. Liu, Z. J. Wu^*, Y. T. Qiu, P. Tian, Q. Liu, Y. Chen, M. Song, M. Hu

^*Corresponding author for this work

Geography, Earth and Environmental Sciences

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Abstract

Nitrate has become the primary inorganic compound in urban aerosol particles, but its effects on particle phase state, which is crucial in multiphase chemistry, remains largely unknown. Herein, particle rebound measurements were conducted to explore the relationship between the liquid–phase–transition threshold relative humidity (RH_threshold) and the inorganic compounds mass fraction in dry particles (F_inorg). Results revealed negative correlations between RH_threshold and F_inorg, with more nitrate leading to lower RH_threshold. Even with RH < 20%, particles with ∼50% nitrate mass fraction remained in non‐solid state. Taking Beijing as an example, decreases were observed in RH_threshold from 64% in 2015 to below 53% nowadays during the moderate‐pollution periods (PM_2.5 = 35–75 μg/m³) due to an enhanced nitrate fraction. This allowed urban aerosol particles to exist in liquid state at lower RH, and consequently, kinetic limitation by bulk diffusion in nitrate‐dominated particles might be negligible, making them key seeds for secondary aerosol formation through multiphase reactions.

Original language	English
Article number	e2023GL105505
Number of pages	11
Journal	Geophysical Research Letters
Volume	50
Issue number	21
Early online date	6 Nov 2023
DOIs	https://doi.org/10.1029/2023gl105505
Publication status	Published - 16 Nov 2023

Bibliographical note

Acknowledgments:
This work is supported by the following projects: National Natural Science Foundation of China (Grants 42205102 and 91844301) and the Fine Particle Research Initiative in East Asia Considering National Differences (FRIEND) Project (NRF-2020M3G1A1114548).

Keywords

phase state
diffusion coefficient
particulate nitrate
urban aerosol
liquid water content

UN SDGs

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title = "Enhanced Nitrate Fraction: Enabling Urban Aerosol Particles to Remain in a Liquid State at Reduced Relative Humidity",

abstract = "Nitrate has become the primary inorganic compound in urban aerosol particles, but its effects on particle phase state, which is crucial in multiphase chemistry, remains largely unknown. Herein, particle rebound measurements were conducted to explore the relationship between the liquid–phase–transition threshold relative humidity (RHthreshold) and the inorganic compounds mass fraction in dry particles (Finorg). Results revealed negative correlations between RHthreshold and Finorg, with more nitrate leading to lower RHthreshold. Even with RH < 20%, particles with ∼50% nitrate mass fraction remained in non‐solid state. Taking Beijing as an example, decreases were observed in RHthreshold from 64% in 2015 to below 53% nowadays during the moderate‐pollution periods (PM2.5 = 35–75 μg/m3) due to an enhanced nitrate fraction. This allowed urban aerosol particles to exist in liquid state at lower RH, and consequently, kinetic limitation by bulk diffusion in nitrate‐dominated particles might be negligible, making them key seeds for secondary aerosol formation through multiphase reactions.",

keywords = "phase state, diffusion coefficient, particulate nitrate, urban aerosol, liquid water content",

author = "Liu, {Y. C.} and Wu, {Z. J.} and Qiu, {Y. T.} and P. Tian and Q. Liu and Y. Chen and M. Song and M. Hu",

note = "Acknowledgments: This work is supported by the following projects: National Natural Science Foundation of China (Grants 42205102 and 91844301) and the Fine Particle Research Initiative in East Asia Considering National Differences (FRIEND) Project (NRF-2020M3G1A1114548). ",

year = "2023",

month = nov,

day = "16",

doi = "10.1029/2023gl105505",

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T2 - Enabling Urban Aerosol Particles to Remain in a Liquid State at Reduced Relative Humidity

AU - Liu, Y. C.

AU - Wu, Z. J.

AU - Qiu, Y. T.

AU - Tian, P.

AU - Liu, Q.

AU - Chen, Y.

AU - Song, M.

AU - Hu, M.

N1 - Acknowledgments: This work is supported by the following projects: National Natural Science Foundation of China (Grants 42205102 and 91844301) and the Fine Particle Research Initiative in East Asia Considering National Differences (FRIEND) Project (NRF-2020M3G1A1114548).

PY - 2023/11/16

Y1 - 2023/11/16

N2 - Nitrate has become the primary inorganic compound in urban aerosol particles, but its effects on particle phase state, which is crucial in multiphase chemistry, remains largely unknown. Herein, particle rebound measurements were conducted to explore the relationship between the liquid–phase–transition threshold relative humidity (RHthreshold) and the inorganic compounds mass fraction in dry particles (Finorg). Results revealed negative correlations between RHthreshold and Finorg, with more nitrate leading to lower RHthreshold. Even with RH < 20%, particles with ∼50% nitrate mass fraction remained in non‐solid state. Taking Beijing as an example, decreases were observed in RHthreshold from 64% in 2015 to below 53% nowadays during the moderate‐pollution periods (PM2.5 = 35–75 μg/m3) due to an enhanced nitrate fraction. This allowed urban aerosol particles to exist in liquid state at lower RH, and consequently, kinetic limitation by bulk diffusion in nitrate‐dominated particles might be negligible, making them key seeds for secondary aerosol formation through multiphase reactions.

AB - Nitrate has become the primary inorganic compound in urban aerosol particles, but its effects on particle phase state, which is crucial in multiphase chemistry, remains largely unknown. Herein, particle rebound measurements were conducted to explore the relationship between the liquid–phase–transition threshold relative humidity (RHthreshold) and the inorganic compounds mass fraction in dry particles (Finorg). Results revealed negative correlations between RHthreshold and Finorg, with more nitrate leading to lower RHthreshold. Even with RH < 20%, particles with ∼50% nitrate mass fraction remained in non‐solid state. Taking Beijing as an example, decreases were observed in RHthreshold from 64% in 2015 to below 53% nowadays during the moderate‐pollution periods (PM2.5 = 35–75 μg/m3) due to an enhanced nitrate fraction. This allowed urban aerosol particles to exist in liquid state at lower RH, and consequently, kinetic limitation by bulk diffusion in nitrate‐dominated particles might be negligible, making them key seeds for secondary aerosol formation through multiphase reactions.

KW - phase state

KW - diffusion coefficient

KW - particulate nitrate

KW - urban aerosol

KW - liquid water content

U2 - 10.1029/2023gl105505

DO - 10.1029/2023gl105505

M3 - Article

SN - 0094-8276

VL - 50

JO - Geophysical Research Letters

JF - Geophysical Research Letters

IS - 21

M1 - e2023GL105505

ER -

Enhanced Nitrate Fraction: Enabling Urban Aerosol Particles to Remain in a Liquid State at Reduced Relative Humidity

Abstract

Bibliographical note

Keywords

UN SDGs

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