Seasonal and diurnal variations of particulate nitrate and organic matter at the IfT research station Melpitz

Abstract

Ammonium nitrate and several organic compounds such as dicarboxylic acids (e.g. succinic acid, glutaric acid), some Polycyclic Aromatic Hydrocarbon (PAHs) or some <i>n</i>-alkanes are semi-volatile. The transition of these compounds between the gas and particulate phase may significantly change the aerosol particles radiative properties, the heterogeneous chemical properties, and, naturally, the total particulate mass concentration. To better assess these time-dependent effects, three intensive field experiments were conducted in 2008–2009 at the Central European EMEP research station Melpitz (Germany) using an Aerodyne Aerosol Mass Spectrometer (AMS). Data from all seasons highlight organic matter as being the most important particulate fraction of PM<sub>1</sub> in summer (59%) while in winter, the nitrate fraction was more prevalent (34.4%). The diurnal variation of nitrate always showed the lowest concentration during the day while its concentration increased during the night. This night increase of nitrate concentration was higher in winter (ΔNO<sub>3</sub><sup>−</sup> = 3.6 μg m<sup>−3</sup>) than in summer (ΔNO<sub>3</sub><sup>−</sup> = 0.7 μg m<sup>−3</sup>). The variation in particulate nitrate was inherently linked to the gas-to-particle-phase equilibrium of ammonium nitrate and the dynamics of the atmosphere during day. The results of this study suggest that during summer nights, the condensation of HNO<sub>3</sub> and NH<sub>3</sub> on pre-existing particles represents the most prevalent source of nitrate, whereas during winter, nighttime chemistry is the predominant source of nitrate. During the summer 2008's campaign, a clear diurnal evolution in the oxidation state of the organic matter became evident (Organic Mass to Organic Carbon ratio (<i>OM/OC</i>) ranging from 1.65 during night to 1.80 during day and carbon oxidation state (OSc) from −0.66 to −0.4), which could be correlated to hydroxyl radical (OH) and ozone concentrations, indicating a photochemical transformation process. In summer, the organic particulate matter seemed to be heavily influenced by regional secondary formation and transformation processes, facilitated by photochemical production processes as well as a diurnal cycling of the substances between the gas and particulate phase. In winter, these processes were obviously less pronounced (<i>OM/OC</i> ranging from 1.60 to 1.67 and OSc from −0.8 to −0.7), so that organic matter apparently originated mainly from aged particles and long range transport

Analysis of exceedances in the daily PM<sub>10</sub> mass concentration (50 μg m<sup>−3</sup>) at a roadside station in Leipzig, Germany

“…The summer data reveals two peculiarities: First, nitrate is largely absent in PM 10 , which is very likely due to the partitioning into the gas phase at high temperatures (Flechard and Fowler, 1998). Aerosol mass spectrometric measurements in Melpitz (Poulain et al, 2011) confirmed that the gas phase partitioning of nitrate is mainly a temperature-driven effect and does occur not only on a seasonal cycle but also on a diurnal cycle.…”

Transformations of Aerosol Particles from an Outdoor to Indoor Environment

“…During winter, proportionally lower percentages of NR-organics were observed outdoors (winter: 36%; summer: 51%); this can be attributed to the increases in concentrations of other inorganic species such as NO 3 -and NH 4 + during this period. The outdoor share of NO 3 -significantly decreased from winter to summer (winter: 32%; summer: 13%); this can be explained by the lower temperatures in winter supporting the aerosol phase of NH 4 NO 3 over the gaseous phase (Stelson and Seinfeld, 1982;Huang et al, 2004;Poulain et al, 2011). In addition, this phase transformation was responsible for the low concentrations of NO 3 -observed indoors during both seasons, with higher constant average temperatures indoors, lower relative humidity, and HNO 3 acid-surface reactions all acting to increase dissociation rates (Hering and Cass, 1999;Smolík et al, 2008).…”

“…Moreover, outdoor aerosol composition affects indoor particle concentration and composition (Brauer et al, 1991;Vette et al, 2001;Morawska et al, 2003;Hussein et al, 2006) with stable compounds such as elemental carbon and SO 4 2-favoured over semivolatile polycylic aromatic hydrocarbons and NO 3 -A Talbot et al, Aerosol and Air Quality Research, 17: 653-665, 2017 654 (Huang et al, 2007;Lunden et al, 2008;Poulain et al, 2011;Zhu et al, 2012;Han et al, 2016). In addition, seasonal variability influences outdoor aerosol composition (Poulain et al, 2011;Talbot et al, 2016) which adds further uncertainties to indoor measurements because of the influence of the phase shift of semivolatile species and the water content of hydrophilic particles (Li and Hopke, 1993;Tsai et al, 2012).…”

Seasonal variations in high time-resolved chemical compositions, sources, and evolution of atmospheric submicron aerosols in the megacity Beijing

“…S3-S5) of the results between the AMS and other instruments also prove the reliability of CEs used here. Pieber et al (2016) found that the CO + 2 interference related to NH 4 NO 3 sampling on the vaporizer showed a median of +3.4 % relative to nitrate, and highly varied between instruments and with operation history (percentiles P 10−90 = +0.4 to +10.2 %). The effect of NH 4 NO 3 on CO + 2 ion signal was quite limited (about 1-2 %) and not considered here.…”