Nitrate Dynamics in UK Urban Environments
Nitrate Dynamics in UK Urban Environments
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英国城市环境中的硝酸盐动态
DOI：
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
D. Fowler
中科院分区：
文献类型：
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作者：
E. Nemitz;G. Phillips;R. Thomas;C. Marco;Y. S. Tang;H. Coe;J. D. Allan;R. Harrison;D. Fowler
硝酸盐对PM2.5和PM10的浓度有重要贡献，对人类健康和区域气候强迫具有重要意义。这对于欧洲西北部尤其如此，那里大量的NH3和NOx排放联合收割机与极低的温度和高相对湿度相结合，创造了有利于NH 4 NO3生产的条件。尽管它的重要性，大多数大气化学模型仍然没有模拟NH 4 NO3非常好，这表明动态仍然没有正确表示。此外，由于其不断变化的平衡，有在亚网格尺度上运行的过程，因此难以模拟。
在这次演讲中，我们回顾了城市环境中硝酸盐动态的新证据，利用最近的城市实地研究的数据，主要是，但不限于，在英国。这一新的面貌是通过使用新的测量技术实现的，如气溶胶质谱法（AMS）、气溶胶化学化合物的城市涡动协方差通量测量和长期硝酸盐测量。
我们量化的相对贡献NH 4 NO3英国气溶胶，审查现有的英国AMS数据库和数据，从英国和欧洲的扩散管/过滤器网络。
对英国两个城市地区内外的气溶胶浓度进行了成对的长期测量（伦敦和爱丁堡; Tang等人，2008年），提供了关于城市NO3增量的信息。测量结果表明，平均而言：
NO3-（城市）= 1.13 × NO3-（农村）+ 0.58 μg m-3，
在冬季的几个月里比在夏季有更大的增加。
通过气溶胶质谱法测量亚微米非难熔NO3-的尺寸分布经常显示在100至300 nm范围内的NO3-尺寸模式的周期，除了在300至800 nm的累积模式。这表明，NO3-是由冷凝的燃烧模式，这是普遍的交通源附近形成。偶尔观察到的罚款NO3-模式，似乎与寒冷，潮湿的条件和大气逆温。
城市地区在产生NH 4 NO3中的作用进一步得到城市地区上方气溶胶化学化合物的不断增长的数据库的支持，通过气溶胶质谱法（例如Nemitz等人，2008年），这表明大多数城市的NO3-排放量，但在几天之间变化很大（与有机气溶胶的排放不同）。
在REPARTEE活动期间，伦敦市中心上方的垂直梯度测量（将165 m处的电信塔测量值与地面城市背景测量值进行比较）显示塔上的NO3-浓度较高，可能是由于较高高度处的较冷温度将气体/气溶胶平衡向气溶胶相转移。
我们还提出的证据表明，NH 4 NO3的命运是受其解离潜力。在温暖的条件下，NH 4 NO3在沉积过程中挥发到地面附近的半自然植被中，由于沉积，温度升高，NH3和HNO 3的浓度降低。这大大增加了NH 4 NO3气溶胶的有效沉积速率，并大大降低了其在大气中的寿命。由于这种挥发近地面不能解决目前的CTM，它建议，有效的沉积速率需要纳入模型来考虑这种影响。
Nitrate makes a significant contribution to the concentration of PM2.5 and PM10 with important implications for human health and regional climate forcing. This is particularly true for NW Europe, where large emissions of NH3 and NOx combine with comparably low temperatures and high relative humidities to create conditions that favour the production of NH4NO3. Despite its importance, most atmospheric chemistry models are still not modelling NH4NO3 very well, indicating that dynamics are still not represented correctly. In addition, due to its changing equilibrium, there are processes which operated at a sub-grid scale and are therefore difficult to simulate.
In this presentation we review new evidence on nitrate dynamics in urban environments, drawing on data from recent urban field studies, mainly, but not exclusively, in the UK. This new look is enabled through the use of new measurement technology such as Aerosol Mass Spectrometry (AMS), urban eddy-covariance flux measurements of aerosol chemical compounds and long-term nitrate measurements.
We quantify the relative contribution NH4NO3 to the UK aerosol, reviewing the existing UK AMS database and data from UK and European denuder/filter-pack networks.
Paired long-term measurements of aerosol concentrations in and outside of two UK urban areas (London & Edinburgh; Tang et al., 2008), have provided information on the urban NO3- increment. The measurements indicate that, on average:
NO3-(urban) = 1.13 × NO3-(rural) + 0.58 μg m-3,
with somewhat larger increments during the winter months than during summer.
Measurements of the size-distributions of sub-micron non-refractory NO3- by aerosol mass spectrometry frequently show periods of a NO3- size mode in the range 100 to 300 nm, in addition to the accumulation mode at 300 to 800 nm. This suggests that NO3- is formed by condensation on the combustion mode which is prevalent near traffic sources. The fine NO3- mode is sporadically observed, and appears to correlate with cold, humid conditions and atmospheric inversions.
The role of urban areas in producing NH4NO3 is further supported by the growing database of aerosol chemical compounds above urban areas, by aerosol mass spectrometry (e.g. Nemitz et al., 2008), which suggests emission of NO3- from most cities, which is nevertheless highly variable between days (unlike the emission of organic aerosol).
Vertical gradient measurements above the city centre of London during the REPARTEE campaign (comparing measurements on the Telecom tower at 165 m with ground-based urban background measurements) show higher NO3- concentrations on the tower, possibly due to colder temperatures at higher heights shifting the gas/aerosol equilibrium towards the aerosol phase.
We also present evidence that the fate of NH4NO3 is affected by its dissociation potential. In warm conditions, NH4NO3 volatilises during the deposition process to semi-natural vegetation near the ground, where temperatures are raised and concentrations of NH3 and HNO3 lowered due to deposition. This greatly increases the effective deposition rate of NH4NO3 aerosol and greatly decreases its atmospheric lifetime. Since this volatilisation near the ground cannot be resolved by current CTMs, it is suggested that effective deposition rates need to be incorporated into models to account for this effect.