Acid gases and aerosol measurements in the UK (1999–2015): regional distributions and trends
<p>The UK Acid Gases and Aerosol Monitoring Network (AGANet) was established in 1999 (12 sites, increased to 30 sites from 2006), to provide long-term national monitoring of acid gases (HNO<sub>3</sub>, SO<sub>2</sub>, HCl) and aerosol components (NO<sub>3</...
Main Authors: | , , , , , , , , , , , , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2018-11-01
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Series: | Atmospheric Chemistry and Physics |
Online Access: | https://www.atmos-chem-phys.net/18/16293/2018/acp-18-16293-2018.pdf |
Summary: | <p>The UK Acid Gases and Aerosol
Monitoring Network (AGANet) was established in 1999 (12 sites, increased to
30 sites from 2006), to provide long-term national monitoring of acid gases
(HNO<sub>3</sub>, SO<sub>2</sub>, HCl) and aerosol components (NO<sub>3</sub><sup>−</sup>,
SO<sub>4</sub><sup>2−</sup>, Cl<sup>−</sup>, Na<sup>+</sup>, Ca<sup>2+</sup>, Mg<sup>2+</sup>).
An extension of a low-cost denuder-filter pack system (DELTA) that is used to
measure NH<sub>3</sub> and NH<sub>4</sub><sup>+</sup> in the UK National Ammonia Monitoring
Network (NAMN) provides additional monthly speciated measurements for the
AGANet. A comparison of the monthly DELTA measurement with averaged daily
results from an annular denuder system showed close agreement, while the sum
of HNO<sub>3</sub> and NO<sub>3</sub><sup>−</sup> and the sum of NH<sub>3</sub> and
NH<sub>4</sub><sup>+</sup> from the DELTA are also consistent with previous filter pack
determination of total inorganic nitrogen and total inorganic ammonium,
respectively. With the exception of SO<sub>2</sub> and SO<sub>4</sub><sup>2−</sup>, the
AGANet provides, for the first time, the UK concentration fields and seasonal
cycles for each of the other measured species. The largest concentrations of
HNO<sub>3</sub>, SO<sub>2</sub>, and aerosol NO<sub>3</sub><sup>−</sup> and SO<sub>4</sub><sup>2−</sup> are
found in southern and eastern England and smallest in western Scotland and Northern
Ireland, whereas HCl are highest in south-eastern, south-western, and central
England, that may be attributed to dual contribution from anthropogenic (coal
combustion) and marine sources (reaction of sea salt with acid gases to form
HCl). Na<sup>+</sup> and Cl<sup>−</sup> are spatially correlated, with largest
concentrations at coastal sites, reflecting a contribution from sea salt.
Temporally, peak concentrations in HNO<sub>3</sub> occurred in late winter and
early spring attributed to photochemical processes. NO<sub>3</sub><sup>−</sup> and
SO<sub>4</sub><sup>2−</sup> have a spring maxima that coincides with the peak in
concentrations of NH<sub>3</sub> and NH<sub>4</sub><sup>+</sup>, and are therefore likely
attributable to formation of NH<sub>4</sub>NO<sub>3</sub> and (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub> from
reaction with higher concentrations of NH<sub>3</sub> in spring. By contrast,
peak concentrations of SO<sub>2</sub>, Na<sup>+</sup>, and Cl<sup>−</sup> during winter
are consistent with combustion sources for SO<sub>2</sub> and marine sources in
winter for sea salt aerosol. Key pollutant events were captured by the
AGANet. In 2003, a spring episode with elevated concentrations of
HNO<sub>3</sub> and NO<sub>3</sub><sup>−</sup> was driven by meteorology and transboundary
transport of NH<sub>4</sub>NO<sub>3</sub> from Europe. A second, but smaller episode
occurred in September 2014, with elevated concentrations of SO<sub>2</sub>,
HNO<sub>3</sub>, SO<sub>4</sub><sup>2−</sup>, NO<sub>3</sub><sup>−</sup>, and NH<sub>4</sub><sup>+</sup> that was
shown to be from the Icelandic Holuhraun volcanic eruptions. Since 1999,
AGANet has shown substantial decrease in SO<sub>2</sub> concentrations relative
to HNO<sub>3</sub> and NH<sub>3</sub>, consistent with estimated decline in UK
emissions. At the same time, large reductions and changes in the aerosol
components provide evidence of a shift in the particulate phase from
(NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub> to NH<sub>4</sub>NO<sub>3</sub>. The potential for NH<sub>4</sub>NO<sub>3</sub> to
release NH<sub>3</sub> and HNO<sub>3</sub> in warm weather, together with the
surfeit of NH<sub>3</sub> also means that a larger fraction of the reduced and
oxidized N is remaining in the gas phase as NH<sub>3</sub> and HNO<sub>3</sub> as
indicated by the increasing trend in ratios of NH<sub>3</sub> : NH<sub>4</sub><sup>+</sup> and
HNO<sub>3</sub> : NO<sub>3</sub><sup>−</sup> over the 16-year period. Due to different removal
rates of the component species by wet and dry deposition, this change is
expected to affect spatial patterns of pollutant deposition with consequences
for sensitive habitats with exceedance of critical loads of acidity and
eutrophication. The changes are also relevant for human health effects
assessment, particularly in urban areas as NH<sub>4</sub>NO<sub>3</sub> constitutes a
significant fraction of fine particulate matter ( < 2.5 µm) that are
linked to increased mortality from respiratory and cardiopulmonary diseases.</p> |
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ISSN: | 1680-7316 1680-7324 |