| 摘要: | 摘要： In this study, we investigated the seasonal, diurnal, and episodic characteristics of aerosol nitrate concentrations in PM2.5 at a suburban receptor site in Hong Kong using an hourly MARGA sampled dataset. At the site, large spikes in the NO3− concentration have been observed in all seasons, and are easily overlooked in datasets examining 24 h average concentrations. As a key component to PM2.5, nitrate constituted between 5 and 12% of the mass concentration on average per month, but contributed up to 25% during some episodic cases spanning only a few hours. Seasonal variations of PM2.5 nitrate concentrations at the site were driven by temperature and excess [NH4+] in the aerosol, defined as the amount of ammonium in excess of that required for satisfying [NH4+]/[SO42−] = 1.5. The vast majority of winter nitrate data was associated with ammonium-rich aerosols ([NH4+]/[SO42−] > 1.5), with the diurnal variation tracking the availability of excess [NH4+]. Distinctly different than winter conditions, the summer nitrate data was in ammonium-poor regime and tracked nitric acid concentrations, a photochemical tracer. A regression analysis of measured nitrate with the excess [NH4+] shows good correlation in spring, summer and winter (R2: 0.72–0.81), with slopes greater than 0.7 indicating the majority of excess NH4+ is associated with PM2.5 nitrate. It was found that measured nitrate exceeded excess [NH4+] in samples of low excess [NH4+] availability, leading to our finding that nitric acid attaching to sea salt and crustal particles in the fine mode is a non-negligible route (constituting up to ∼20% of the PM2.5 nitrate in this study) to assimilate nitrate into the PM2.5 aerosol. Accounting for both this minor route and the ammonia + nitric acid route may prove useful in modeling efforts to capture PM2.5 nitrate measurement fluctuations, particularly during events of a large influx of alkali particles, such as dust storms. [Display omitted] •Seasonal, diurnal, and episodic PM2.5 nitrate trends are characterized.•PM2.5 nitrate seasonal and diurnal trends track NH4+ availability and temperature.•Episodic nitrate events occur throughout sampling period but persist more in winter.•HNO3 adding to dust/sea salt particles is found to be important to PM2.5 nitrate.
出版者： Elsevier Ltd
出版日期： 2015-12
出處： Atmospheric environment (1994), 2015-12, Vol.122, p.864-875
資源來源： Elsevier ScienceDirect Journals Complete - Autoholdings
版權： 2015 Elsevier Ltd
識別號： ISSN: 1352-2310
識別號： EISSN: 1873-2844
識別號： DOI: 10.1016/j.atmosenv.2015.02.009 |
