Reply to "Comment on 'Long-term atmospheric measurements of C-1-C-5 alkyl nitrates in the Pearl River Delta region of southeast China'"

National Center for Atmospheric Research, Boulder, CO 80307, USA
Atmospheric Environment (Impact Factor: 3.28). 03/2006; 40(9):1619-1632. DOI: 10.1016/j.atmosenv.2005.10.062


Mixing ratios of seven C1–C5 alkyl nitrates (RONO2) were measured during a 16-month study (August 2001–December 2002) at Tai O, a coastal site 30km west of central Hong Kong in the Pearl River Delta, the fastest-growing industrial region in the world. The C3–C4 (rather than C1–C2) RONO2 were most abundant throughout the study, showing the importance of photochemical (rather than marine) RONO2 production in the sampled air. A lack of methyl nitrate (MeONO2) enhancement during summer, when the prevailing winds are from the ocean, indicates that the South China Sea is not a region of strong RONO2 emissions. By contrast, MeONO2 levels during pollution episodes (up to 25 parts per trillion by volume (pptv)) were the highest that our group has recorded during urban photochemical RONO2 production, as opposed to marine emissions or biomass burning. The highest summed RONO2 level of the study (204pptv) was measured in the afternoon of 7 November 2002, during an intense pollution episode that captured the highest ozone (O3) level ever recorded in Hong Kong (203ppbv). During pollution episodes, the average ratio of O3 to summed RONO2 was roughly 1000:1 in freshly polluted air (ethyne/CO∼3–5pptv/ppbv) and 500:1 in very freshly polluted air (ethyne/CO∼6–8pptv/ppbv). Ozone and RONO2 share a common photochemical source, and their good correlation in pollution plumes shows that RONO2 can be used as a tracer of photochemical O3 production. Even MeONO2 showed similar diurnal variations as the C2–C5 RONO2, indicating a strong photochemical source despite its very slow photochemical production from methane oxidation. The decomposition of longer-chain alkoxy radicals also does not explain the high MeONO2 levels, and rough calculations show that methoxy radical reaction with NO2 appears to be a viable alternate pathway for MeONO2 production in polluted atmospheres, though further measurements and modeling are required to confirm this mechanism.

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    • "Among all of the RONO 2 , 2-PrONO 2 and 2-BuONO 2 were the most abundant at the two sites, consistent with the results observed in different environments (Blake et al., 2003; Simpson 15 et al., 2006; Russo et al., 2010; Wang et al., 2013). The relatively higher levels of 2- PrONO 2 and 2-BuONO 2 were expected due to the balance of increased branching ratios for photochemical RONO 2 formation and the decreased lifetime of both parent alkanes and RONO 2 with increasing carbon numbers (Arey et al., 2001; Simpson et al., 2006; Russo et al., 2010). The average RONO 2 mixing ratios at TMS were much higher 20 than those measured in forest areas in coastal New England (Russo et al., 2010) and in tropospheric air influenced by Asian outflow during the airborne TRACE-P mission (Simpson et al., 2003), where the levels of parent hydrocarbons were lower. "
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    ABSTRACT: Alkyl nitrates (RONO2) were measured concurrently at a mountain site (TMS) and an urban site (TW) at the foot of the same mountain in Hong Kong from September to November 2010, when high O3 mixing ratios were frequently observed. The abundance and temporal patterns of five C1–C4 RONO2 and their parent hydrocarbons (RH), the RONO2/RH ratios and photochemical age of air masses at TMS differed from those at TW, reflecting different contributions of direct emissions and secondary formation of RONO2 at the two sites. Relative to 2-BuONO2/n-butane, the measured ratios of C1–C2 RONO2/RH at the two sites exhibited significant positive deviations from pure photochemical (PP) curves and background initial ratio (BIR) curves obtained from laboratory kinetic data, suggesting that background mixing ratios had a significant influence on the RONO2 and RH distributions. In contrast to the C1–C2 RONO2/RH ratios, the evolution for the measured ratios of C3 RONO2/RH to 2-BuONO2/n-butane agreed well with the ratio distributions in the PP and BIR curves at the two sites. Furthermore, the ratios of 1-/2-PrONO2 and yields of 1- and 2-PrONO2 suggested that the C3 RONO2 were mainly from secondary formation at TMS, whereas secondary formation and other additional sources had a significant influence on C3 RONO2 mixing ratios at TW. The source apportionment results confirmed that secondary formation was the dominant contributor to all the RONO2 at TMS, while most of the RONO2 at TW were from secondary formation and biomass burning. The findings of the source apportionments and photochemical evolution of RONO2 are helpful to evaluate photochemical processing in Hong Kong using RONO2 as an indicator.
    Full-text · Article · Aug 2015 · Atmospheric Chemistry and Physics
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    • "The trace gases were re-volatilized using a hot water bath and then reproducibly split into five streams for detection. Generally, organic nitrates have been measured by high-resolution (HR) gas chromatography (GC) with electron capture detection (ECD) (De Kock and Anderson 1994; Moschonas and Glavas 2000; Glavas 2001; Glavas and Moschonas 2001; Fischer et al. 2002; Simpson et al. 2006; Russo et al. 2010; Zhang et al. 2013) and a combination of GC-ECD and GC-MS (Luxenhofer et al. 1994, 1996; Schneider et al. 1998; Schneider and Ballschmiter 1999; Fischer et al. 2000). Both traditional injections of a concentrated extract (De Kock and Anderson 1994; Luxenhofer et al. 1994, 1996; Schneider et al. 1998; Schneider and Ballschmiter 1999), as well as thermal desorption from adsorption traps and cryo-trapping, have been applied in the "
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    ABSTRACT: The daily and seasonal atmospheric concentrations, deposition fluxes and emission sources of a few C3-C9 gaseous alkyl nitrates (ANs) at the Belgian coast (De Haan) on the Southern North Sea were determined. An adapted sampler design for low- and high-volume air-sampling, optimized sample extraction and clean-up, as well as identification and quantification of ANs in air samples by means of gas chromatography mass spectrometry, are reported. The total concentrations of ANs ranged from 0.03 to 85 pptv and consisted primarily of the nitro-butane and nitro-pentane isomers. Air mass backward trajectories were calculated by the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model to determine the influence of main air masses on AN levels in the air. The shorter chain ANs have been the most abundant in the Atlantic/Channel/UK air masses, while longer chain ANs prevailed in continental air. The overall mean N fluxes of the ANs were slightly higher for summer than those for winter-spring, although their contributions to the total nitrogen flux were low. High correlations between AN and HNO2 levels were observed during winter/spring. During summer, the shorter chain ANs correlated well with precipitation. Source apportionment by means of principal component analysis indicated that most of the gas phase ANs could be attributed to traffic/combustion, secondary photochemical formation and biomass burning, although marine sources may also have been present and a contributing factor.
    Full-text · Article · Jun 2014 · Environmental Monitoring and Assessment
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    • "ANs are usually considered to be the temporary reservoir of reactive nitrogen species and they can regenerate NO x through photolysis and oxidation. [5] [45] Because compared to NO x they have relatively long atmospheric lifetimes, ranging from several days to weeks, [22] [46] [47] ANs may be transported large distances to remote regions of the atmosphere, potentially providing a source of NO x to these areas and influencing O 3 chemistry. Therefore, ANs play a significant role in the NO x –O 3 –HO x cycle in both polluted and remote atmospheres. "
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    ABSTRACT: Alkyl nitrates (ANs) are important nitrogen-containing organic compounds and are usually considered to be temporary reservoirs of reactive nitrogen NOx (NO2 and NO) in the atmosphere, although their atmospheric fates are incompletely understood. Here a laboratory study of the gas-phase photolysis and OH-initiated reactions of methyl nitrate (CH3ONO2) and ethyl nitrate (C2H5ONO2), as models of atmospheric ANs, is reported with a focus on elucidating the detailed photochemical reaction mechanisms of ANs in the atmosphere. A series of intermediate and end products were well characterised for the first time from the photochemical reactions of methyl and ethyl nitrate conducted under simulated atmospheric conditions. Notably, for both the photolysis and OH-initiated reactions of CH3ONO2 and C2H5ONO2, unexpectedly high yields of HNO3 (photochemically non-reactive nitrogen) were found and also unexpectedly high yields of peroxyacyl nitrates (RC(O)OONO2, where R = H, CH3, CH3CH2,...) (reactive nitrogen) have been found as CH3C(O)OONO2 in the C2H5ONO2 reaction or proposed as HC(O)OONO2 in the CH3ONO2 reaction. Although the yields of HNO3 from the ANs under ambient conditions are likely variable and different from those obtained in the laboratory experiments reported here, the results imply that the ANs could potentially serve as a sink for reactive nitrogen in the atmosphere. The potential for this dual role of organic nitrates in the nitrogen cycle should be considered in the study of air quality and nitrogen exchange between the atmosphere and surface. Finally, an attempt was made to estimate the production of HNO3 and peroxyacyl nitrates derived from NOx by ANs as intermediates in the atmosphere.
    Full-text · Article · Nov 2011 · Environmental Chemistry
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