Research ArticleENVIRONMENTAL SCIENCE

Reactive nitrogen chemistry in aerosol water as a source of sulfate during haze events in China

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Science Advances  21 Dec 2016:
Vol. 2, no. 12, e1601530
DOI: 10.1126/sciadv.1601530
  • Fig. 1 Characteristic features of a major haze event in Beijing, China (January 2013).

    (A) Sulfate/sulfur dioxide ratio ([SO42−]/[SO2]) and (B) midday ozone (O3) concentrations (10:00 to 15:00 local time) and nitrogen dioxide (NO2) concentrations at different fine-particle (PM2.5) concentration levels. (C) Correlation of the unexplained sulfate concentration (ΔSO42− = observation − model) (see sections M2 and M3) with aerosol droplet solution and AWC (color-coded). (D) Anion-to-cation ratio in PM2.5 as observed in Beijing (solid symbols) and in other studies in northern China (open symbols) (table S1) compared to the characteristic ratios reported for aircraft measurements in the Arctic of outflow from East Asia, Europe, and North America (solid red, blue, and green lines; here, only NH4+, NO3, and SO42− were considered) (87).

  • Fig. 2 Aqueous-phase sulfate production by sulfur dioxide oxidation under characteristic conditions.

    Sulfate production rates for (A) cloud droplets and (B) Beijing haze plotted against pH value.

    Light blue– and gray-shaded areas indicate characteristic pH ranges for cloud water under clean to moderately polluted conditions and aerosol water during severe haze episodes in Beijing, respectively. The colored lines represent sulfate production rates calculated for different aqueous-phase reaction pathways with oxidants: hydrogen peroxide (H2O2), ozone (O3), transition metal ions (TMIs), and nitrogen dioxide (NO2). Characteristic reactant concentrations and model calculations for clouds and haze are taken from the literature and observations, and specified in Materials and Methods (see sections M7 to M9) (12, 21).

  • Fig. 3 Importance of the NO2 reaction pathway for sulfate production in the Beijing haze (January 2013).

    Sulfate production rates calculated for the aqueous-phase NO2 reaction pathway (pH 5.8) and the gas-phase OH reaction pathway compared to the missing source of sulfate. Crosses and circles represent hourly production rates calculated on the basis of measurement data, and the diamonds represent the average missing source (arithmetic mean ± SD) (see sections M3 to M5) (7). The pink-shaded area shows the maximum and minimum sulfate production rates by the NO2 reaction pathway bounded by the aerosol water pH ranging from 5.4 to 6.2 during haze periods.

  • Fig. 4 Conceptual model of sulfate formation in haze events in NCP.

    The traditional OH, H2O2, and O3 reaction pathways in atmospheric gas phase and cloud chemistry are included here, as well as the NO2 reaction pathway in aerosol water with elevated pH and NO2 concentrations proposed in this study.

Supplementary Materials

  • Supplementary material for this article is available at hhttp://advances.sciencemag.org/cgi/content/full/2/12/e1601530/DC1

    fig. S1. Weakened photochemistry by aerosol dimming effects during January 2013 in Beijing.

    fig. S2. Importance of the NO2 reaction pathway for sulfate production in the Beijing haze (January 2013).

    fig. S3. Influence of ionic strength (I) on rate of aqueous sulfate-producing reactions.

    fig. S4. Estimation of Fe3+ and Mn2+ concentrations as a function of aerosol water pH during Beijing hazes.

    fig. S5. Regional pollution across the NCP during January 2013.

    fig. S6. Annual precipitation pH of China in 2013.

    fig. S7. The same as Fig. 2 but with a lower limit of reaction rate constants reported by Lee and Schwartz (18).

    table S1. Previously reported concentrations of cations and anions in PM2.5 during winter for cities in NCP used in Fig. 1D.

    table S2. Summary of field observation and methods in this study.

    table S3. Domain, configurations, and major dynamic and physical options used in WRF v3.5.1.

    table S4. Rate expression and rate coefficients of relevant aqueous-phase reactions.

    table S5. Constants for calculating the apparent Henry’s constant (H*).

    table S6. Summary of suggested activity coefficient (a)–ionic strength (I) dependence.

    table S7. Influence of ionic strength (I) on rate of aqueous sulfate-producing reactions.

    References (108128)

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Weakened photochemistry by aerosol dimming effects during January 2013 in Beijing.
    • fig. S2. Importance of the NO2 reaction pathway for sulfate production in the Beijing haze (January 2013).
    • fig. S3. Influence of ionic strength (I) on rate of aqueous sulfate-producing reactions.
    • fig. S4. Estimation of Fe3+ and Mn2+ concentrations as a function of aerosol water pH during Beijing hazes.
    • fig. S5. Regional pollution across the NCP during January 2013.
    • fig. S6. Annual precipitation pH of China in 2013.
    • fig. S7. The same as Fig. 2 but with a lower limit of reaction rate constants reported by Lee and Schwartz (18).
    • table S1. Previously reported concentrations of cations and anions in PM2.5 during winter for cities in NCP used in Fig. 1D.
    • table S2. Summary of field observation and methods in this study.
    • table S3. Domain, configurations, and major dynamic and physical options used in WRF v3.5.1.
    • table S4. Rate expression and rate coefficients of relevant aqueous-phase reactions.
    • table S5. Constants for calculating the apparent Henry’s constant (H*).
    • table S6. Summary of suggested activity coefficient (a)–ionic strength (I) dependence.
    • table S7. Influence of ionic strength (I) on rate of aqueous sulfate-producing reactions.
    • References (108–128)

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