Elsevier

Science of The Total Environment

Volume 656, 15 March 2019, Pages 129-139
Science of The Total Environment

Observations of C1–C5 alkyl nitrates in the Yellow River Delta, northern China: Effects of biomass burning and oil field emissions

https://doi.org/10.1016/j.scitotenv.2018.11.208Get rights and content

Highlights

  • The tempo-spatial variations of C1-C5 alkyl nitrates and parent hydrocarbons were examined in the Yellow River Delta.

  • Oil field emissions and biomass burning are important sources of hydrocarbons and alkyl nitrates in this region.

  • Besides parent hydrocarbons, longer alkanes are important precursors of alkyl nitrates in oil fields.

Abstract

Alkyl nitrates (RONO2) are important reservoirs of nitrogen oxides and play key roles in the tropospheric chemistry. Two phases of intensive campaigns were conducted during February–April and June–July of 2017 at a rural coastal site and in open oil fields of the Yellow River Delta region, northern China. C1–C5 alkyl nitrates showed higher concentration levels in summer than in winter-spring (p < 0.01), whilst their parent hydrocarbons showed an opposite seasonal variation pattern. The C3–C5 RONO2 levels in the oil fields were significantly higher than those in the ambient rural air. Alkyl nitrates showed well-defined diurnal variations, elucidating the effects of in-situ photochemical production and regional transport of aged polluted plumes. Backward trajectory analysis and fire maps revealed the significant contribution of biomass burning to the observed alkyl nitrates and hydrocarbons. A simplified sequential reaction model and an observation-based chemical box model were deployed to diagnose the formation mechanisms of C1–C5 RONO2. The C3–C5 RONO2 were mainly produced from the photochemical oxidation of their parent hydrocarbons (i.e., C3–C5 alkanes), whilst C1–C2 RONO2 compounds have additional sources. In addition to parent hydrocarbons, longer alkanes with >4 carbon atoms were also important precursors of alkyl nitrates in the oil fields. This study demonstrates the significant effects of oil field emissions and biomass burning on the volatile organic compounds and alkyl nitrate formation, and provides scientific support for the formulation of control strategies against photochemical air pollution in the Yellow River Delta region.

Introduction

Alkyl nitrates (RONO2) are an important family member of the reactive odd nitrogen (NOy = NO + NO2 + NO3 + N2O5 + HONO + HNO3 + NO3 + PANs + RONO2 + etc.), which are crucial players of atmospheric chemistry and have significant consequences to regional air quality, ecosystem, and climate change (Jenkin and Clemitshaw, 2000). They have relatively low chemical reactivity, and can release NO2 via photolysis (Atkinson et al., 2006; Sommariva et al., 2008). Due to this nature, alkyl nitrates can serve as temporary reservoirs of nitrogen oxides (NOx = NO + NO2) during long-range transport, re-distribute NOx between urban and rural (or remote) areas, and hence affect the regional and even global ozone (O3) formation (Day et al., 2003). Thus, investigation of characteristics and sources of alkyl nitrates is an important step towards better understanding of the formation of regional photochemical pollution.

In the troposphere, alkyl nitrates are mainly formed through photochemical degradation of volatile organic compounds (VOCs) in the presence of NOx (Arey et al., 2001; Atkinson et al., 2006). Briefly, oxidation of hydrocarbons by the hydroxyl radical (OH) produces a RO2 radical, which can then react with NO to yield RONO2 (Arey et al., 2001). For each RONO2 species, there are only a small number of precursor hydrocarbons, the degradation of which can exactly yield the specific RO2 radical (e.g., CH3O2 for methyl nitrate, C2H5O2 for ethyl nitrate, etc.). In general, the longer and more complex is the chain of the RO2 radical, the fewer are the precursor hydrocarbons of the RONO2 species. For instance, the formation of the longer-chain (e.g., ≥C3) RONO2 is usually dominated by the oxidation of parent alkanes (e.g., propane for PrONO2, butane for BuONO2, pentane for PeONO2, etc.), whilst C1–C2 RONO2 can be formed from the other VOCs that can decompose to CH3O2 and C2H5O2 radicals, in addition to their parent alkanes (i.e., methane and ethane) (Russo et al., 2010; Sun et al., 2018). Besides, ambient alkyl nitrates are also subject to primary emissions in specific circumstances. In coastal areas, for example, marine emissions are an important source of shorter-chain RONO2, especially methyl nitrate (Atlas et al., 1993; Blake et al., 2003; Song et al., 2018). Biomass burning has been also recognized as a significant source contributing to the ambient RONO2 (Simpson et al., 2002). Identification of the principal sources and secondary formation mechanisms is fundamental to formulating the control strategies against alkyl nitrate pollution in a specific region.

In recent decades, photochemical air pollution characterized by high concentrations of O3 and other secondary pollutants (such as PANs and RONO2, etc.) has become a major environmental concern in China, as a result of its fast urbanization process (Wang et al., 2006; Wang et al., 2017; Xue et al., 2014a). A number of field studies have been carried out to evaluate the characteristics and formation mechanisms of O3 pollution in the fast developing regions of China, such as the Jing-Jin-Ji region, Pearl River Delta, and Yangtze River Delta (Wang et al., 2017; and references therein), whilst relatively limited efforts have focused on alkyl nitrates (Ling et al., 2016; Lyu et al., 2015; Sun et al., 2018; Wang et al., 2013). The Yellow River Delta region (YelRD) is located in the mouth of the Yellow River in Shandong province, and lies in between the Shandong Peninsula and Beijing-Tianjin area (see Fig. 1). With a population of 10 million, it is home to the second largest oil field (Shengli Oil Field) in China with numerous refinery and petrochemical plants, and now is one of the most economically dynamic regions in China. It is also an important agricultural area and a coastal wetland in northern China. Given the above features, it can be expected that the YelRD region should be suffering from serious air pollution problems, especially photochemical pollution. To the best of our knowledge, however, there have been no previous studies to investigate the photochemical pollution in this region and evaluate the impacts of the oil extraction and petrochemical industries.

To investigate the photochemical air pollution and its formation mechanisms in the YelRD region, intensive field campaigns were conducted at a rural site surrounded by oil fields and directly in the open oil fields during selected months of 2017. A large suite of air pollutants and meteorological parameters were measured in-situ. This paper analyzes the tempo-spatial variations, sources, and secondary formation regimes of C1–C5 RONO2 in the YelRD region. Elevated concentrations of alkyl nitrates were observed in the oil fields, where longer chain alkanes are important RONO2 precursors besides the well-known short chain parent hydrocarbons. Oil field emissions and biomass burning are major sources of alkyl nitrates and photochemical air pollution in the region. Overall, this study provides some new insights into the characterization and sources of alkyl nitrates in the oil-extracting areas, and can support the formulation of control strategies against photochemical pollution in the YelRD region.

Section snippets

Site description

The sampling campaigns were conducted at the Yellow River Delta Ecology Research Station of Coastal Wetland (37°45′N, 118°58′E; 0 m above sea level), Chinese Academy of Sciences. It is a typical rural coastal site located at the mouth of the Yellow River with few local anthropogenic emissions (see Fig. 1). The closest populated area around our site is a small town with a population of 25,000, 16 km to the southwest. The major nearby urban areas are Dongying city (with 2.1 million population)

General characteristics

Table 3 documents the descriptive statistics of C1–C5 RONO2 and related species observed both at the rural site and in open oil fields. Fig. 2 shows the comparisons of the measured RONO2 species in summer versus in winter-spring and between rural area and oil fields. For the rural site, the C1–C5 RONO2 exhibited higher levels in summer (with average ± standard deviation of 204 ± 93 pptv) than in winter-spring seasons (133 ± 53 pptv). On the contrary, their precursors including C1–C5

Summary

Intensive measurements of C1–C5 RONO2 and related parameters were carried out at a rural site and in open oil fields of the Yellow River Delta region during February–April and June–July of 2017. Alkyl nitrates showed higher mixing ratios in summer than in winter-spring, which is opposite to the seasonal pattern of their parent hydrocarbons. Enhanced levels of heavier C3–C5 RONO2 compounds were observed in the oil fields compared to the rural atmosphere. In-situ photochemical production and

Acknowledgments

The authors thank Yang Changli and Li Rui for their help in the field studies. We thank the University of Leeds for providing the Master Chemical Mechanism (version 3.3.1) and the NOAA Air Resources Laboratory for providing the HYSPLIT model. This work was funded by the National Natural Science Foundation of China (No.: 41675118, 41505111 and 41775140), the National Key Research and Development Program of China (No.: 2016YFC0200500), the Special Public Welfare Item (GYHY201406033-05), the Qilu

References (43)

  • T. Wang et al.

    Ozone pollution in China: a review of concentrations, meteorological influences, chemical precursors, and effects

    Sci. Total Environ.

    (2017)
  • D.R. Worton et al.

    Alkyl nitrate photochemistry during the tropospheric organic chemistry experiment

    Atmos. Environ.

    (2010)
  • L.K. Xue et al.

    On the use of an explicit chemical mechanism to dissect peroxy acetyl nitrate formation

    Environ. Pollut.

    (2014)
  • J. Arey et al.

    Alkyl nitrate, hydroxyalkyl nitrate, and hydroxycarbonyl formation from the NOx-air photooxidations of C5–C8 n-alkanes

    J. Phys. Chem.

    (2001)
  • R. Atkinson et al.

    Atmospheric degradation of volatile organic compounds

    Chem. Rev.

    (2003)
  • R. Atkinson et al.

    Evaluated kinetic and photochemical data for atmospheric chemistry: volume II-gas phase reactions of organic species

    Atmos. Chem. Phys.

    (2006)
  • E. Atlas et al.

    Alkyl nitrates, nonmethane hydrocarbons, and halocarbon gases over the equatorial Pacific Ocean during SAGA 3

    J. Geophys. Res. Atmos.

    (1993)
  • S.B. Bertman et al.

    Evolution of alkyl nitrates with air mass age

    J. Geophys. Res. Atmos.

    (1995)
  • N.J. Blake et al.

    Latitudinal, vertical, and seasonal variations of C1–C4 alkyl nitrates in the troposphere over the Pacific Ocean during PEM-Tropics A and B: Oceanic and continental sources

    J. Geophys. Res. Atmos.

    (2003)
  • J.J. Colman et al.

    Description of the analysis of a wide range of volatile organic compounds in whole air samples collected during PEM-Tropics A and B

    Anal. Chem.

    (2001)
  • P.J. Crutzen et al.

    Biomass burning as a source of atmospheric gases CO, H2, N2O, NO, CH3Cl, and COS

    Nature

    (1979)
  • Cited by (17)

    • Worsening ozone air pollution with reduced NO<inf>x</inf> and VOCs in the Pearl River Delta region in autumn 2019: Implications for national control policy in China

      2022, Journal of Environmental Management
      Citation Excerpt :

      Physical processes such as solar radiation, dry deposition, and planetary boundary layer evolution are also considered in the chemical box model. A detailed description of the model setup is provided elsewhere (Xue et al., 2016; Zhang et al., 2019). Within the MCM model, the net rate of Ox production was calculated as the difference between the rate of Ox production (P(Ox)) and rate of Ox loss (L(Ox)), which were quantified using Equations (S1)–(S2) in the SI.

    • Significant impacts of anthropogenic activities on monoterpene and oleic acid-derived particulate organic nitrates in the North China Plain

      2021, Atmospheric Research
      Citation Excerpt :

      The filter sampling and online measurements at the rural site of DY were conducted in both winter (15–23 January) and summer (4 June–9 July) of 2017. Detailed information of the DY site was given by Zhang et al. (2019). The Jinan (JN) site is situated at the Atmospheric Environment Observatory Station in Shandong University (36°40′ N, 117°03′ E), in Jinan, Shandong Province.

    • Atmospheric nitrous acid (HONO) at a rural coastal site in North China: Seasonal variations and effects of biomass burning

      2020, Atmospheric Environment
      Citation Excerpt :

      The time resolution of all the measurements above was 1 min except for HONO at 30 s, meteorological parameters at 5 min, PM2.5 at 30 min, and water-soluble ions in fine particles at 12 h. More details about their detection limits, precisions, and quality assurance and quality control procedures were provided by Xue et al. (2016) and Zhang et al. (2019). Generally, concentrations of air pollutants (except for O3 and K+ in fine particles) were higher in winter-spring than in summer.

    View all citing articles on Scopus
    View full text