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: 3.06). 03/2006; 40(9):1619-1632. DOI: 10.1016/j.atmosenv.2005.10.062

ABSTRACT 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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    ABSTRACT: To understand the long-term variations of nonmethane hydrocarbons (NMHCs) and their emission sources, real-time speciated NMHCs have been monitored in Hong Kong since 2005. Data analysis showed that the concentrations of C3–C5 and C6–C7 alkanes slightly increased from 2005 to 2013 at a rate of 0.0015 and 0.0005 μg m−3 yr−1 (p < 0.05), respectively, while aromatics decreased at a rate of 0.006 μg m−3 yr−1 (p < 0.05). Positive Matrix Factorization (PMF) model was applied to identify and quantify the NMHC sources. Vehicular exhaust, gasoline evaporation and liquefied petroleum gas (LPG) usage, consumer product and printing, architectural paints, and biogenic emissions were identified and on average accounted for 20.2 ± 6.2%, 25.4 ± 6.3%, 32.6 ± 5.8%, 21.5 ± 4.5%, and 3.3 ± 1.5% of the ambient NMHC concentrations, respectively. From 2005 to 2013, the contributions of both traffic-related sources and solvent-related sources showed no significant changes, different from the trends in emission inventory. On O3 episode days dominated by local air masses, the increase ratio of NMHC species from non-episode to episode days was found to be a natural function of the reactivity of NMHC species, suggesting that photochemical reaction would significantly change the NMHCs composition between emission sources and the receptors. Effect of photochemical reaction loss on receptor-oriented source apportionment analysis needs to be quantified in order to identify the NMHCs emission sources on O3 episode days.
    Atmospheric Environment 02/2015; 103. DOI:10.1016/j.atmosenv.2014.12.048 · 3.06 Impact Factor
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    ABSTRACT: In the fall and winter of 2007 to 2011, 167 24-h quartz filter-based fine particle (PM2.5) samples were collected at a regional background site in the central Pearl River Delta. The PM2.5 showed an annual reduction trend with a rate of 8.58μgm(-3) (p<0.01). The OC component of the PM2.5 reduced by 1.10μgm(-3)yr(-1) (p<0.01), while the reduction rates of sulfur dioxide (SO2) and sulfate (SO4(2-)) were 10.2μgm(-3)yr(-1) (p<0.01) and 1.72μgm(-3)yr(-1) (p<0.01), respectively. In contrast, nitrogen oxides (NOx) and nitrate (NO(3-)) presented growth trends with rates of 6.73μgm(-3)yr(-1) (p<0.05) and 0.79μgm(-3)yr(-1) (p<0.05), respectively. The PM2.5 reduction was mainly related to the decrease of primary OC and SO4(2-), and the enhanced conversion efficiency of SO2 to SO4(2-) was related to an increase in the atmospheric oxidizing capacity and a decrease in aerosol acidity. The discrepancy between the annual trends of NOx and NO3(-) was attributable to the small proportion of NO3(-) in the total nitrogen budget.
    Science of The Total Environment 08/2014; 497-497:274-281. DOI:10.1016/j.scitotenv.2014.08.008 · 3.16 Impact Factor
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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.
    Environmental Monitoring and Assessment 06/2014; 186(10). DOI:10.1007/s10661-014-3866-7 · 1.68 Impact Factor

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