scholarly journals High atmospheric oxidation capacity drives wintertime nitrate pollution in the eastern Yangtze River Delta of China

2021 ◽  
Author(s):  
Han Zang ◽  
Yue Zhao ◽  
Juntao Huo ◽  
Qianbiao Zhao ◽  
Qingyan Fu ◽  
...  
Keyword(s):  
Gas Phase ◽  
Urban Areas ◽  
Yangtze River ◽  
Eastern China ◽  
Yangtze River Delta ◽  
Atmospheric Oxidation ◽  
Formation Mechanisms ◽  
Oxidation Capacity ◽  
Haze Pollution ◽  
Nitrate Aerosol

Abstract. Nitrate aerosol plays an increasingly important role in wintertime haze pollution in China. Despite intensive research on the wintertime nitrate chemistry in recent years, quantitative constraints on the formation mechanisms of nitrate aerosol in the Yangtze River Delta (YRD), one of the most developed and densely populated regions in eastern China, remain inadequate. In this study, we identify the major nitrate formation pathways and their key controlling factors during the winter haze pollution period in the eastern YRD using two-year (2018–2019) field observations and detailed observation-constrained model simulations. We find that the high atmospheric oxidation capacity, coupled with high aerosol liquid water content (ALWC), made both the heterogeneous hydrolysis of dinitrogen pentoxide (N2O5) and the gas-phase OH oxidation of nitrogen dioxide (NO2) important pathways for wintertime nitrate formation in this region, with contribution percentages of 69 % and 29 % in urban areas and 63 % and 35 % in suburban areas, respectively. We further find that the gas-to-particle partitioning of nitric acid (HNO3) was very efficient so that the rate-determining step in the overall formation process of nitrate aerosol was the oxidation of NOx to HNO3 through both heterogeneous and gas-phase processes. The atmospheric oxidation capacity (i.e., the availability of O3 and OH radicals) was the key factor controlling the production rate of HNO3 from both processes. During the COVID-19 lockdown (January–February 2020), the enhanced atmospheric oxidation capacity greatly promoted the oxidation of NOx to nitrate and hence weakened the response of nitrate aerosol to the emission reductions in urban areas. Our study sheds light on the detailed formation mechanisms of wintertime nitrate aerosol in the eastern YRD and highlights the demand for the synergetic regulation of atmospheric oxidation capacity and NOx emissions to mitigate wintertime nitrate and haze pollution in eastern China.

scholarly journals Contribution of nitrous acid to the atmospheric oxidation capacity in an industrial zone in the Yangtze River Delta region of China

2020 ◽  
Vol 20 (9) ◽  
pp. 5457-5475
Author(s):  
Jun Zheng ◽  
Xiaowen Shi ◽  
Yan Ma ◽  
Xinrong Ren ◽  
Halim Jabbour ◽  
...  
Keyword(s):  
Nitrous Acid ◽  
Yangtze River ◽  
Yangtze River Delta ◽  
River Delta ◽  
Atmospheric Oxidation ◽  
Formation Mechanisms ◽  
The Yangtze River ◽  
Industrial Zone ◽  
Oxidation Capacity ◽  
The Yangtze River Delta

Abstract. A suite of instruments was deployed to simultaneously measure nitrous acid (HONO), nitrogen oxides (NOx = NO + NO2), carbon monoxide (CO), ozone (O3), volatile organic compounds (VOCs – including formaldehyde, HCHO) and meteorological parameters near a typical industrial zone in Nanjing in the Yangtze River Delta (YRD) region of China from 1 to 31 December 2015. High levels of HONO were detected using a wet-chemistry-based method. HONO ranged from 0.03 to 7.04 ppbv with an average of 1.32±0.92 ppbv. Elevated daytime HONO was frequently observed with a minimum of several hundred parts per trillion by volume (pptv) on average, which cannot be explained by the homogeneous OH + NO reaction (POH+NO) and primary emissions (Pemission), especially during periods with high particulate matter (PM2.5) loadings. HONO chemistry and its impact on the atmospheric oxidation capacity in the study area were further investigated using a Master Chemical Mechanism (MCM) box model. The results show that the average hydroxyl radical (OH) production rate was dominated by the photolysis of HONO (7.13×106 molec. cm−3 s−1), followed by the ozonolysis of alkenes (3.94×106 molec. cm−3 s−1), the photolysis of O3 (2.46×106 molec. cm−3 s−1) and the photolysis of HCHO (1.60×106 molec. cm−3 s−1) during the campaign period, especially within plumes that originated from the industrial zone. Model simulations indicated that heterogeneous chemistry played an important role in HONO formation. The average nighttime NO2 to HONO conversion rate was determined to be ∼0.8 % h−1. A good correlation between nocturnal HONO∕NO2 and the product of particle surface area density (S∕V) and relative humidity (RH), S/V⋅RH, supports the heterogeneous NO2∕H2O reaction mechanism. The other HONO source, designated as Punknonwn, was about twice as high as POH+NO on average and displayed a diurnal profile with an evidently photo-enhanced feature, i.e., photosensitized reactions of NO2 may be an important daytime HONO source. Nevertheless, our results suggest that daytime HONO formation was mostly due to the light-induced conversion of NO2 on aerosol surfaces, whereas heterogeneous NO2 reactions on the ground surface dominated nocturnal HONO production. Our study indicated that an elevated PM2.5 level during haze events can promote the conversion of NO2 to HONO by providing more heterogeneous reaction sites, thereby increasing the atmospheric oxidation capacity, which may further promote the formation of secondary air pollutants. Highlights: High levels of HONO, with an average of 1.32±0.92 ppbv, were observed near one of the largest industrial zones in the YRD region of China. HONO photolysis and alkene ozonolyses contributed the most to OH production and, hence, the atmospheric oxidation capacity. High loading of PM2.5 provided additional reaction surfaces for HONO formation. Heterogeneous formation mechanisms were the most important daytime HONO sources and were further enhanced by sunlight.

scholarly journals The optical properties, physical properties and direct radiative forcing of urban columnar aerosols in the Yangtze River Delta, China

2018 ◽  
Vol 18 (2) ◽  
pp. 1419-1436 ◽  
Author(s):  
Bingliang Zhuang ◽  
Tijian Wang ◽  
Jane Liu ◽  
Huizheng Che ◽  
Yong Han ◽  
...  
Keyword(s):  
Optical Properties ◽  
Physical Properties ◽  
Yangtze River ◽  
Eastern China ◽  
Yangtze River Delta ◽  
River Delta ◽  
Transfer Model ◽  
Size Distributions ◽  
Haze Pollution ◽  
The Yrd

Abstract. The optical and physical properties as well as the direct radiative forcings (DRFs) of fractionated aerosols in the urban area of the western Yangtze River Delta (YRD) are investigated with measurements from a Cimel sun photometer combined with a radiation transfer model. Ground-based observations of aerosols have much higher temporal resolutions than satellite retrievals. An initial analysis reveals the characteristics of the optical properties of different types of fractionated aerosols in the western YRD. The total aerosols, mostly composed of scattering components (93.8 %), have mean optical depths of 0.65 at 550 nm and refractive index of 1.44 + 0.0084i at 440 nm. The fine aerosols are approximately four times more abundant and have very different compositions from coarse aerosols. The absorbing components account for only  ∼  4.6 % of fine aerosols and 15.5 % of coarse aerosols and have smaller sizes than the scattering aerosols within the same mode. Therefore, fine particles have stronger scattering than coarse ones, simultaneously reflecting the different size distributions between the absorbing and scattering aerosols. The relationships among the optical properties quantify the aerosol mixing and imply that approximately 15 and 27.5 % of the total occurrences result in dust- and black-carbon-dominating mixing aerosols, respectively, in the western YRD. Unlike the optical properties, the size distributions of aerosols in the western YRD are similar to those found at other sites over eastern China on a climatological scale, peaking at radii of 0.148 and 2.94 µm. However, further analysis reveals that the coarse-dominated particles can also lead to severe haze pollution over the YRD. Observation-based estimations indicate that both fine and coarse aerosols in the western YRD exert negative DRFs, and this is especially true for fine aerosols (−11.17 W m−2 at the top of atmosphere, TOA). A higher absorption fraction leads directly to the negative DRF being further offset for coarse aerosols (−0.33 W m−2) at the TOA. Similarly, the coarse-mode DRF contributes to only 13.3 % of the total scattering aerosols but > 33.7 % to the total absorbing aerosols. A sensitivity analysis states that aerosol DRFs are not highly sensitive to their profiles in clear-sky conditions. Most of the aerosol properties and DRFs have substantial seasonality in the western YRD. The results further reveal the contributions of each component of the different size particles to the total aerosol optical depths (AODs) and DRFs. Additionally, these results can be used to improve aerosol modelling performance and the modelling of aerosol effects in the eastern regions of China.

scholarly journals Contribution of HONO to the atmospheric oxidation capacity in an industrial zone in the Yangtze River Delta region of China

2019 ◽  
Author(s):  
Jun Zheng ◽  
Xiaowen Shi ◽  
Yan Ma ◽  
Xinrong Ren ◽  
Halim Jabbour ◽  
...  
Keyword(s):  
Yangtze River ◽  
Yangtze River Delta ◽  
River Delta ◽  
Atmospheric Oxidation ◽  
The Yangtze River ◽  
Industrial Zone ◽  
Delta Region ◽  
Oxidation Capacity ◽  
Yangtze River Delta Region ◽  
The Yangtze River Delta

Abstract. A suite of instruments were deployed to simultaneously measure nitrous acid (HONO), nitrogen oxides (NOx = NO + NO2), carbon monoxide (CO), ozone (O3), volatile organic compounds (VOCs, including formaldehyde (HCHO)) and meteorological parameters near a typical industrial zone in Nanjing of the Yangtze River Delta region, China. High levels of HONO were detected using a wet chemistry-based method. HONO ranged from 0.03–7.04 ppbv with an average of 1.32 ± 0.92 ppbv. Elevated daytime HONO was frequently observed with a minimum of several hundreds of pptv on average, which cannot be explained by the homogeneous OH + NO reaction (POH+NO) alone, especially during periods with high loadings of particulate matters (PM2.5). The HONO chemistry and its impact on atmospheric oxidation capacity in the study area were further investigated using a MCM-box model. The results show that the average hydroxyl radical (OH) production rate was dominated by the photolysis of HONO (7.13×106 molecules cm−3 s−1), followed by ozonolysis of alkenes (3.94×106 molecules cm−3 s−1), photolysis of O3 (2.46×106 molecules cm−3 s−1) and photolysis of HCHO (1.60×106 molecules cm−3 s−1), especially within the plumes originated from the industrial zone. The observed similarity between HONO/NO2 and HONO in diurnal profiles strongly suggests that HONO in the study area was likely originated from NO2 heterogeneous reactions. The average nighttime NO2 to HONO conversion rate was determined to be ~ 0.9 % hr−1. Good correlation between nocturnal HONO/NO2 and the products of particle surface area density (S/V) and relative humidity (RH), S/V·RH, supports the heterogeneous NO2/H2O reaction mechanism. The other HONO source, designated as Punknonwn, was about twice as much as POH+NO on average and displayed a diurnal profile with an evidently photo-enhanced feature, i.e., photosensitized reactions of NO2 may be an important daytime HONO source. Nevertheless, our results suggest that daytime HONO formation was mostly due to the light-induced conversion of NO2 on aerosol surfaces but heterogeneous NO2 reactions on ground surface dominated nocturnal HONO production. Concurred elevated HONO and PM2.5 levels strongly indicate that high HONO may increase the atmospheric oxidation capacity and further promote the formation of secondary aerosols, which may in turn synergistically boost NO2/HONO conversion by providing more heterogeneous reaction sites.

Sign in / Sign up

Export Citation Format

Share Document