 |
| Titel |
Diurnal cycles of ammonia, nitrous acid and nitric acid at a forest site in Finland in summer 2010 |
| VerfasserIn |
Aki Virkkula, Ulla Makkonen, Jenni Mäntykenttä, Hannele Hakola |
| Konferenz |
EGU General Assembly 2011
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250053243
|
|
|
|
|
|
| Zusammenfassung |
| Background
In July – August 2010 a large campaign “Hyytiälä United Measurements of
Photochemistry and Particles in Air - Comprehensive Organic Precursor Emission
Concentration 2010 (HUMPPA – COPEC-10)”, was conducted in a boreal forest at the
SMEAR II station in Hyytiälä, southwestern central Finland. The campaign was organized by
the Max Planck Institute for Chemistry and the University of Helsinki. The general goal was
to study links between gas phase oxidation chemistry and particle properties and
processes.
The Finnish Meteorological Institute contributed to the campaign with an on-line analyzer
MARGA 2S (Ten Brink et al., 2007) for semi-continuous (1-hr time resolution) measurement
of water-soluble gases and ions. Concentrations of gases (HCl, HNO3, HNO2,
NH3, SO2) and major ions in particles (Cl, NO3, SO4, NH4, Na, K, Mg, Ca) were
measured in two size fractions: PM2.5 and PM10. The MARGA has been operational at
SMEAR II since 21 June. Here we discuss data collected until 4 September, 2010,
and restrict the analysis to the nitrogen-containing gases. NH3 plays a key role in
neutralizing acidic atmospheric compounds and in aerosol formation. The concentration of
semi-volatile aerosol species such as ammonium nitrate and ammonium chloride is strongly
dependent on the gas phase precursors, NH3, HNO3 and HCl. HONO is of atmospheric
importance due to its expected significant contribution to the production of OH
radicals.
Results and discussion
The median concentrations of ammonia (NH3), nitrous acid (HONO) and nitric acid
(HNO3) during whole period of 21 June – 4 September were 0.24 ppb, 0.069 ppb and 0.22
ppb, respectively. A very clear diurnal cycle of all these gases was observed, especially in
July. All data were classified according to the measurement hour. In July the highest median
concentration of ammonia, 0.59 ppb was observed in the afternoon at 15:00 and the lowest,
0.17 ppb at 05:00. Similarly, the highest median concentration of nitric acid, 0.32
ppb was observed at 15:00 and the lowest, 0.20 ppb at 04:00. The clear diurnal
cycles of ammonia and nitric acid suggest that they may at least partly be due to
evaporation of ammonium nitrate particles in the hottest time of the warm July 2010 and
condensation on particles at the cooler night. For nitrous acid the diurnal variation was the
opposite: the highest median concentration 0.20 ppb was observed very early in
the morning at 03:00 and the minimum concentration 0.045 ppb in the evening at
18:00, in agreement with the photolysis of HONO. Towards the end of the campaign
both the concentrations and their diurnal variations decreased. In 25 August to 04
September the median concentrations of ammonia, nitrous acid and nitric acid were 0.10
ppb, 0.061 ppb, and 0.18 ppb, respectively. From the 24-hour classification the
medians of daily maximum and minimum concentrations were 0.16 and 0.069 ppb for
ammonia, 0.094 and 0.021 ppb for nitrous acid, and 0.20 and 0.17 ppb for nitric
acid.
Acknowledgement
This work was supported by the Academy of Finland as part or the Centre of Excellence
program (project no 1118615).
Reference
Ten Brink H., Otjes R., Jongejan P., Slanina S. (2007) An instrument for semi-continuous
monitoring of the size-distribution of nitrate, ammonium, sulphate and chloride in aerosol,
Atm. Environ. 41, 2768-2779. |
|
|
|
|
|
|