Variation in global chemical composition of PM<sub>2.5</sub>: emerging results from SPARTAN
The Surface PARTiculate mAtter Network (SPARTAN) is a long-term project that includes characterization of chemical and physical attributes of aerosols from filter samples collected worldwide. This paper discusses the ongoing efforts of SPARTAN to define and quantify major ions and trace metals f...
| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-08-01
|
| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/16/9629/2016/acp-16-9629-2016.pdf |
| Summary: | The Surface PARTiculate mAtter Network (SPARTAN) is a long-term project that
includes characterization of chemical and physical attributes of aerosols
from filter samples collected worldwide. This paper discusses the
ongoing efforts of SPARTAN to define and quantify major ions and trace
metals found in fine particulate matter (PM<sub>2.5</sub>). Our methods infer the
spatial and temporal variability of PM<sub>2.5</sub> in a cost-effective manner.
Gravimetrically weighed filters represent multi-day averages of PM<sub>2.5</sub>,
with a collocated nephelometer sampling air continuously. SPARTAN
instruments are paired with AErosol RObotic NETwork (AERONET) sun
photometers to better understand the relationship between ground-level
PM<sub>2.5</sub> and columnar aerosol optical depth (AOD).<br><br>We have examined the chemical composition of PM<sub>2.5</sub> at 12 globally
dispersed, densely populated urban locations and a site at Mammoth Cave (US)
National Park used as a background comparison. So far, each SPARTAN location has
been active between the years 2013 and 2016 over periods of 2–26 months,
with an average period of 12 months per site. These sites have collectively
gathered over 10 years of quality aerosol data. The major PM<sub>2.5</sub>
constituents across all sites (relative contribution ± SD) are
ammoniated sulfate (20 % ± 11 %), crustal material (13.4 % ± 9.9 %), equivalent black carbon (11.9 % ± 8.4 %),
ammonium nitrate (4.7 % ± 3.0 %), sea salt (2.3 % ± 1.6 %), trace element oxides (1.0 % ± 1.1 %), water (7.2 % ± 3.3 %) at 35 % RH, and residual matter (40 % ± 24 %).<br><br>Analysis of filter samples reveals that several PM<sub>2.5</sub> chemical
components varied by more than an order of magnitude between sites.
Ammoniated sulfate ranges from 1.1 µg m<sup>−3</sup> (Buenos Aires,
Argentina) to 17 µg m<sup>−3</sup> (Kanpur, India in the dry season). Ammonium
nitrate ranged from 0.2 µg m<sup>−3</sup> (Mammoth Cave, in summer) to 6.8
µg m<sup>−3</sup> (Kanpur, dry season). Equivalent black carbon ranged from
0.7 µg m<sup>−3</sup> (Mammoth Cave) to over 8 µg m<sup>−3</sup> (Dhaka,
Bangladesh and Kanpur, India). Comparison of SPARTAN vs. coincident
measurements from the Interagency Monitoring of Protected Visual
Environments (IMPROVE) network at Mammoth Cave yielded a high degree of
consistency for daily PM<sub>2.5</sub> (<i>r</i><sup>2</sup> = 0.76, slope = 1.12), daily
sulfate (<i>r</i><sup>2</sup> = 0.86, slope = 1.03), and mean fractions of all major
PM<sub>2.5</sub> components (within 6 %). Major ions generally agree well with
previous studies at the same urban locations (e.g. sulfate fractions agree
within 4 % for 8 out of 11 collocation comparisons). Enhanced
anthropogenic dust fractions in large urban areas (e.g. Singapore, Kanpur,
Hanoi, and Dhaka) are apparent from high Zn : Al ratios.<br><br>The expected water contribution to aerosols is calculated via the
hygroscopicity parameter <i>κ</i><sub>v</sub> for each filter. Mean aggregate
values ranged from 0.15 (Ilorin) to 0.28 (Rehovot). The all-site parameter
mean is 0.20 ± 0.04. Chemical composition and water retention in each
filter measurement allows inference of hourly PM<sub>2.5</sub> at 35 % relative
humidity by merging with nephelometer measurements. These hourly PM<sub>2.5</sub>
estimates compare favourably with a beta attenuation monitor (MetOne) at the
nearby US embassy in Beijing, with a coefficient of variation <i>r</i><sup>2</sup> = 0.67 (<i>n</i> = 3167), compared to <i>r</i><sup>2</sup> = 0.62 when <i>κ</i><sub>v</sub> was
not considered. SPARTAN continues to provide an open-access database of
PM<sub>2.5</sub> compositional filter information and hourly mass collected from a
global federation of instruments. |
|---|---|
| ISSN: | 1680-7316 1680-7324 |