Chemical and Light Extinction Characteristics of Atmospheric Aerosols in Suburban Nanjing, China
Abstract
:1. Introduction
2. Methodology
2.1. Aerosol Sampling
2.2. Chemical Analysis
2.3. Data Analysis
2.3.1. IMPROVE Formula
2.3.2. Koschmieder’s Formula
2.3.3. Backward Trajectory and Clustering Analysis
3. Results and Discussion
3.1. Chemical Characteristics of Atmospheric Aerosol
3.1.1. Size-Segregated Mass Concentrations
3.1.2. Seasonal Differences
3.1.3. Day–Night Differences
3.2. Light Extinction Estimated by the IMPROVE Formula
3.2.1. Reconstruction of PM2.5 Mass
3.2.2. Estimation of Extinction Coefficients
3.3. Variations of Chemical and Light Extinction Characteristics under Different Circumstances
3.3.1. Influences of Different Pollution Levels
3.3.2. Influences of Different Air Masses
4. Conclusions
- PM2.5 dominated the aerosol pollution, with its highest mass concentration in winter, followed by summer, spring, and autumn. Concentrations of most chemical components were highest in winter too, except that the highest SO42− concentration occurred in summer, K+ and Mg2+ peaked in spring while Ca2+ reached its maximum in autumn. Mass concentrations of PM2.5 and most major species were higher during nighttime than daytime due to unfavorable conditions for pollutant diffusion. For NO3−, its loading was much lower during daytime, owing to its semi-volatile behavior and/or possible nocturnal heterogeneous production. However, SO42− concentration was higher during daytime, indicating the significant photochemical production.
- The measured species can reconstruct the total PM2.5 mass well, and OM, (NH4)2SO4, and NH4NO3 comprised the majority of PM2.5 (75.6%) with another significant component of FS contributing ~18%, and two minor components of SS and EC both occupying ~3%. The IMPROVE formula could estimate the aerosol light extinction reasonably well, with (NH4)2SO4, NH4NO3, and OM contributing 33.2%, 25.1%, and 24.9%, respectively. The light extinction was dominated by the SNA, indicating a significant role of secondary ions in visibility degradation.
- Mass concentrations of PM2.5 and all species increased gradually with the increase of haze pollution levels. The increase of SNA was particularly remarkable, and NO3− appeared to arise most rapidly among all species. Regarding the light extinction, the contribution from OM continuously decreased, while SNA, in particular nitrate contribution, increased with the increase of pollution levels, indicating a significant role of secondary species in haze formation and also underscoring the priority of reduction of vehicular NO2 emissions in Nanjing.
- Four clusters of air masses were identified, with differing chemical and light extinction characteristics. The local air mass and air mass originated from Bohai, but travelled through Shandong Province and north of Jiangsu Province appeared to be heavily polluted. The local air mass had high mass loadings of OC and EC and, correspondingly with OM, contributing most to the light extinction. The air mass from Bohai was contributed mainly by the SNA in terms of both mass concentration and light extinction. The air parcel from Huanghai was relatively clean, but with significant light extinction contributed by SO42−. The air mass starting from the northwest was the cleanest and clearest, and carbonaceous aerosols seemed to contribute most to its light extinction.
Supplementary Materials
Acknowledgments
Author Contributions
Conflicts of Interest
References
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Components | Mean ± SD | |||
---|---|---|---|---|
Winter (Number = 79) | Spring (Number = 108) | Summer (Number = 123) | Autumn (Number = 132) | |
PM2.5 | 166.0 ± 96.3 | 97.4 ± 35.9 | 100.4 ± 40.8 | 85.3 ± 44.4 |
SO42− | 23.3 ± 19.6 | 15.7 ± 8.32 | 24.3 ± 9.51 | 14.5 ± 7.89 |
NO3− | 29.0 ± 22.8 | 10.9 ± 7.85 | 12.2 ± 11.3 | 13.3 ± 12.0 |
NH4+ | 16.7 ± 8.37 | 9.18 ± 4.12 | 13.1 ± 5.36 | 12.5 ± 7.45 |
Na+ | 0.73 ± 0.30 | 0.55 ± 0.26 | 0.59 ± 0.78 | 0.36 ± 0.11 |
K+ | 1.99 ± 1.02 | 2.03 ± 2.17 | 1.60 ± 1.40 | 1.01 ± 0.43 |
Mg2+ | 0.09 ± 0.04 | 0.10 ± 0.07 | 0.06 ± 0.05 | 0.08 ± 0.04 |
Ca2+ | 0.75 ± 0.60 | 1.06 ± 0.55 | 0.50 ± 0.28 | 1.43 ± 0.75 |
F- | 0.11 ± 0.08 | 0.08 ± 0.09 | 0.07 ± 0.06 | 0.06 ± 0.03 |
Cl− | 3.55 ± 2.15 | 1.36 ± 1.41 | 1.15 ± 1.59 | 1.39 ± 1.44 |
OC | 21.5 ± 12.9 | 15.0 ± 7.54 | 13.6 ± 8.24 | 12.7 ± 6.87 |
EC | 5.10 ± 3.30 | 3.95 ± 2.72 | 2.88 ± 1.50 | 2.06 ± 1.00 |
SOC | 6.66 ± 6.61 | 4.23 ± 4.38 | 5.06 ± 4.82 | 4.44 ± 4.16 |
SOC/OC | 28.9 ± 16.1% | 27.4 ± 19.2% | 33.7 ± 18.4% | 32.8 ± 16.0% |
Season | Time | Temperature/°C | Relative Humidity (%) | Wind Velocity (m·s−1) | Mixed Layer Height (m) 1 | Rainfall (mm) 2 |
---|---|---|---|---|---|---|
Winter | Day | 6.3 | 49.0 | 1.8 | 962.3 | 116.8 |
Night | 2.4 | 66.8 | 1.0 | 153.3 | ||
Spring | Day | 22.2 | 36.3 | 2.0 | 1384.7 | 136.4 |
Night | 17.3 | 51.4 | 1.7 | 135.2 | ||
Summer | Day | 27.8 | 59.8 | 1.4 | 1361.2 | 405.5 |
Night | 24.0 | 78.9 | 1.1 | 147.3 | ||
Autumn | Day | 20.1 | 56.2 | 1.7 | 1194.1 | 170.6 |
Night | 15.9 | 78.5 | 1.2 | 155.3 |
Haze Grades | Distinguishing Criteria | Day (Proportion, %) | PM2.5 (μg·m−3) | NH4+ (μg·m−3) | NO3− (μg·m−3) | SO42− (μg·m−3) | OC (μg·m−3) | EC (μg·m−3) | RH 1 (%) | WS (m·s−1) | MLH (m) |
---|---|---|---|---|---|---|---|---|---|---|---|
Non_haze | V > 10.0 2 | 18 (27.7) | 69.9 | 7.25 | 6.58 | 9.66 | 9.27 | 2.06 | 56.3 | 2.29 | 1082.2 |
Slight | 5.0 ≤ V < 10.0 | 32 (49.2) | 98.0 | 11.9 | 12.4 | 17.9 | 14.5 | 3.16 | 62.3 | 1.35 | 1279.9 |
Mild | 3.0 ≤ V < 5.0 | 11 (16.9) | 132.8 | 19.2 | 22.3 | 25.5 | 16.6 | 3.31 | 69.7 | 1.37 | 1041.0 |
Moderate | 2.0 ≤ V < 3.0 | 3 (4.6) | 165.4 | 23.2 | 34.6 | 30.9 | 20.4 | 4.25 | 66.6 | 1.68 | 841.7 |
Severe | V < 2.0 | 1 (1.5) | 383.7 | 23.8 | 80.3 | 72.7 | 45.5 | 9.44 | 75.4 | 0.38 | 772.0 |
Mass Source | PM2.5 (μg·m−3) | NH4+ (μg·m−3) | NO3− (μg·m−3) | SO42− (μg·m−3) | OC (μg·m−3) | EC (μg·m−3) | RH (%) | WS (m·s−1) | MLH (m) |
---|---|---|---|---|---|---|---|---|---|
1 | 94.3 | 12.4 | 12.7 | 19.1 | 12.1 | 2.52 | 68.0 | 1.48 | 1227.1 |
2 | 119.7 | 14.3 | 17.9 | 19.4 | 18.8 | 4.06 | 56.3 | 1.39 | 1079.4 |
3 | 120.1 | 13.4 | 17.9 | 21.5 | 15.6 | 3.37 | 65.1 | 1.39 | 1147.5 |
4 | 86.2 | 7.90 | 8.41 | 10.2 | 13.2 | 3.30 | 48.3 | 2.48 | 1391.4 |
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Wu, D.; Zhang, F.; Ge, X.; Yang, M.; Xia, J.; Liu, G.; Li, F. Chemical and Light Extinction Characteristics of Atmospheric Aerosols in Suburban Nanjing, China. Atmosphere 2017, 8, 149. https://doi.org/10.3390/atmos8080149
Wu D, Zhang F, Ge X, Yang M, Xia J, Liu G, Li F. Chemical and Light Extinction Characteristics of Atmospheric Aerosols in Suburban Nanjing, China. Atmosphere. 2017; 8(8):149. https://doi.org/10.3390/atmos8080149
Chicago/Turabian StyleWu, Dan, Fan Zhang, Xinlei Ge, Meng Yang, Junrong Xia, Gang Liu, and Fengying Li. 2017. "Chemical and Light Extinction Characteristics of Atmospheric Aerosols in Suburban Nanjing, China" Atmosphere 8, no. 8: 149. https://doi.org/10.3390/atmos8080149