the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 18 Apr 2024
Assessing the influence of long-range transport of aerosols on the PM2.5 chemical composition and concentration in the Aburrá Valley
Abstract. Assessing long-range transport (LRT) of pollutants recognizes that multiple sources of varying scale and location can impact air quality. In the Aburrá Valley, Colombia, and other cities in Northern South America, biomass burning (BB), dust, and volcanic degassing have been identified as sources of LRT of aerosols. However, the impact of these sources on air quality and their characterization have yet to be thoroughly studied. This work investigates the influence of these sources on the chemical composition of PM2.5 during annual and intra-annual high-load aerosol events. We identified, tracked, and meteorologically characterized LRT events and evaluated their influence on PM2.5 concentration and chemical composition. We ran a Positive Matrix Factorization (PMF) for each kind of event, identifying high contribution in organic carbon (OC1, OC2), F- and secondary aerosols trace SO42- and NO3- for the BB events, crustal mineral along with Ti and Ca contribution for dust events and SO42-, Na, Al and Ca for volcanic events. The increasing concentration of some ions and toxic heavy metals (Cr, Mn, Cd, and Ni) were also related to BB and volcanic degassing influence. During these LRT events, the BB fraction of PM2.5 dominates by frequency and amount, averaging 11.14 μg / m3 (38 %). On average, dust and volcanic degassing contribute 6.77 μg / m3 (34 %) and 6.46 μg / m3 (30 %) of the concentrations. Of the three, dust events showed fewer affected days. The study highlighted hotspot zones such as the Orinoco and Middle Magdalena Valley for BB aerosols, the Caribbean for dust, and the Nevado del Ruíz volcano for volcanic aerosols. This study gives insights for future chemical transport modeling studies in the region and supports strategies to manage internal and external pollution sources and effects for the Aburrá Valley and the region.
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Status: open (until 30 May 2024)
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RC1: 'Comment on egusphere-2024-695', Anonymous Referee #2, 29 Apr 2024
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Review of Manuscript Entitled: Assessing the influence of long-range transport of aerosols on the PM2.5 chemical composition and concentration in the Aburrá Valley
General comments:
The manuscript presents the results of utilizing multiple tools, from in-situ PM2.5 chemical speciation data, source-receptor models, and back trajectory analysis, to estimate the monthly contribution of LRT to PM2.5 concentration in the Aburrá Valley, in Colombia. Furthermore, a careful characterization of the prevailing meteorological conditions during LRT events from Biomass Burning, Dust, and Volcanic degassing where also shown in the manuscript.
The manuscript is well written (some minor comments below) and advances the current understanding of the contribution of regional an global sources of PM2.5 in the Northern South American region. Particularly, the study points to the relevance of volcanic degassing for the region, an often overlooked source of aerosols, which is shown by the authors to be significant during LRT events.
The figures shown in the manuscript are of great quality.
As an overall recommendation, I would invite the authors to focus less on the importance of their findings for the AV, and rather focus on discussing the broader implications of their work for the region. That could be achieved with relatively ease but would require re-writing some specific parts of the document.
I recommend the manuscript to be published after addressing these minor comments.
Specific comments:
L10. “During these LRT events, the BB fraction of PM2.5 dominates by frequency and amount, averaging 11.14 µg/m3 (38%). On average, dust and volcanic degassing contribute 6.77 µg/m3 (34%) and 6.46 µg/m3 (30%) of the concentrations.” This phrase might be confusing, specially the second part. What the authors really mean is that averaging over LRT events, dust and volcanic degassing contribute 34% and 30% of PM2.5? Is that the total? Something should be said in the abstract to at least provide the reader with an idea of the observed frequency of LRT events, or its typical duration (so those other numbers could be better contextualized).
L12. “Of the three, dust events showed fewer affected days.” I would consider rewriting.
L63. “In Colombia, the Aburrá Valley (AV) has made substantial progress in monitoring and identifying agents of the state of air quality in the territory, managing to report significant affectation driven by external sources (SIATA, 2021).” Consider re-writing or removing altogether.
L64 “In the territory, as on the national scale” To which territory do the authors refer to? Please, consider removing or rewriting.
L65. There are at least 2 relevant studies in the region that could possibly enrich the discussion in the introduction:
- https://doi.org/10.1016/j.atmosenv.2019.01.051 which demonstrate the high concentration of PM2.5 and ozone in the Orinoco river basin during high BB seasons.
- https://doi.org/10.5194/acp-20-7459-2020 which shows the correlation of BB tracers with regional biomass burning activity.
L71. “To the AV, obtaining the …” Consider removing “To the AV”.
L90. It would be useful to qualify this statement with data. For example, how many daily exceedances were observed in a given year? Or what is the annual mean PM2.5 concentration in the AV?
L107. “However, the sampling in this later period was typically between 3 to 14 days. Therefore, while the temporal sampling resolution did decrease with time, we still have periods of intense sampling and measurements across the majority of the period.” Please rephrase as it is confusing.
L123. “Official campaign concentrations of PM2.5 were measured by a Low Volume PM2.5 ambient air sampler”. Could the authors clarify this statement? What are “official” concentrations? How do the Low-vol concentrations differ from the High-volume sampler derived concentrations? Where the latter concentrations not determined at all? Please clarify and correct the manuscript accordingly.
L125. “In addition to the carbonaceous matter, species measured included secondary organic carbon”. Please re-write for clarity. SOC was not measured, but it was inferred from the measurements.
L150. “mean absolute percentage error of 21.5%”. Is this 21.5 percent overestimation relative to the MED-BEME station? Or 21% underestimation?
L187. “Here, if less than four days with values greater than the specified threshold were detected, then they were classed as outliers and removed (i.e., we are focusing on LRT events, which we define as lasting more than half a week”. This is a key point in the manuscript and one that should be subject to a more specific description. Why focus on 4-day events? Dust events from LRT can impact a given location for a single day but contribute over 90% of PM2.5 to that given location on that day. If the decision is due to the sparsity of PM2.5 samples, then it should be clearly stated.
Figure 4. Caption and legend could be improved. No mention is made of the PM2.5 variable there. Is it monthly PM2.5 for the site? Or is ir PM2.5 attributable to LRT events? Similarly, the “All events” bar, which is black, it is not clear if there were any LRT events in which the three sources were impacting the site simultaneously.
L315. Seasonality?
L315. “some non-event days in the different months occur” ?? Please, consider re-writing for clarity.
L353. “On the other hand, the concentration of PM2.5 right after Volcanic-LRT significantly decreases” …. This assertion is hard to see from Figure 7c.
L442. “The lower TCSO2 threshold derived in this study is likely linked to the CAMS product we used”. It is also possible that using SO2 observations (if available from the monitoring network) for the Volcanic-LRT events could help.
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