Increased atmospheric PM2.5 events due to open waste burning in Qaanaaq, Greenland, summer of 2022

High levels of particulate matter (PM) are relevant to severe air pollution and can adversely impact human health. Maintaining healthy air quality for the residents of the Arctic region is essential to satisfy the no‐one‐left‐behind policy of the Sustainable Development Goals (SDGs) by the United Nations. In this study, we installed a PM2.5 measurement system in Qaanaaq, Greenland, and obtained the first continuous PM2.5 measurements from July 20, 2022 to August 13, 2022. We observed several increased PM2.5 events; relatively high PM2.5 levels persisted from August 8, 2022. On the same day, visible black smoke emitted from the Qaanaaq dump site originated from open waste burning. By confirming less transboundary air pollution contributions from remote aerosol source regions to Qaanaaq during the measurement period using NOAA's HYSPLIT backward trajectory analysis and NASA's MERRA‐2 aerosol re‐analysis, we confirmed that the increased PM2.5 was primarily due to local open waste burning with less contributions from transboundary air pollution. However, small contributions from biomass burning outside Greenland were plausible during the early measurement period. Additionally, NOAA's HYSPLIT dispersion calculations suggested possible aerosol depositions from local open waste burning to nearby sea areas, such as Baffin Bay. Although the hourly mean PM2.5 mass concentration was not alarmingly high during the measurement period, future studies should incorporate longer‐term continuous PM2.5 measurements along with other atmospheric chemical analyses to identify possible local air pollution sources in detail to ensure clean ambient air for the future in the Arctic. Our study provides quantitative evidence of the impact of open waste burning on air quality at a study site in Greenland, which could be crucial in developing air quality policies for this region in the Arctic.

Globally, ambient air pollutants were associated with 3.3 million premature deaths in 2010 (Lelieveld et al., 2015).Mortality rates due to ambient air pollution increased to 4.2 million in 2019, according to the World Health Organization (WHO) (https://www.who.int/news-room/factsheets/detail/ambient-(outdoor)-air-quality-and-health).A recent study estimated 2.89 million premature deaths globally due to PM 2.5 in 2019, with China and India accounting for 40% and 23% of these deaths, respectively (Yang et al., 2022).Lelieveld et al. (2015) projected that these mortality rates could double by 2050 compared with those estimated for 2010.
Particulate matter (PM) and ozone are major air pollutants (Lelieveld et al., 2015) associated with respiratoryand cardiovascular-related diseases (Brunekreef & Holgate, 2002).PM, comprising many different aerosols, has been associated with both air quality and climate change, though its chemical components and overall impacts on climate change require further investigation (Fuzzi et al., 2015).The latest model-based study, using bias-corrected simulations of PM 2.5 (defined as suspended particles in aerodynamic diameters smaller than 2.5 μm: WHO, 2006a), reported a global estimate of 7.7 million premature deaths as of 2015 (Im et al., 2023).This was consistent with PM 2.5 -related mortality rates estimated from 41 cohort studies (corresponding to 16 countries) using the Global Exposure Mortality Model (Burnett et al., 2018).However, as one of the short-lived climate forcers, atmospheric aerosols also impact climate via changes in radiative forcing (IPCC, 2021).Therefore, PM is an important factor in environmental, atmospheric, and climate research, particularly owing to its worldwide impact.
PM 2.5 environmental standards (ES) have been established to allow the objective assessment of their impacts on human health, corresponding to both long-term (i.e., annual mean ES: 10 μg m À3 ) and short-term (24-h mean ES, i.e., daily mean: 25 μg m À3 ) PM 2.5 exposures (WHO, 2006b).These exposure ES thresholds have been updated to stricter values as per the new guidelines (5 and 15 μg m À3 , respectively) in 2021 (WHO, 2021).The WHO PM 2.5 ESs (WHO, 2006b(WHO, , 2021) ) are stricter than those determined by some national agencies such as the US Environmental Protection Agency (https://www.epa.gov/pm-pollution/national-ambient-air-quality-standardsnaaqs-pm) and the Japan Ministry of the Environment (https://www.env.go.jp/kijun/taiki4.html).
Many PM 2.5 observations have been conducted, but most are concentrated in the mid-latitudes, especially in the northern hemisphere (Lary et al., 2014;WHO, 2016).However, the high latitudes of the Arctic and surrounding regions frequently experience summer wildfires that emit aerosols, such as carbonaceous aerosols (BC: black carbon; OC: organic carbon) (Yasunari et al., 2018(Yasunari et al., , 2021(Yasunari et al., , 2022)).Recently, wildfire-weather interactions due to the aerosol radiative effect (Huang et al., 2023) and BC's heating effect have been reported to change local meteorological conditions (Tan et al., 2022;Wang et al., 2023).Even during winter, increased PM 2.5 has been observed in Alaska, along with the development of an inversion layer (Tran & Mölders, 2011).The "noone-left-behind" policy of the Sustainable Development Goals (SDGs) by the United Nations for 2030 (https:// sdgs.un.org/2030agenda) includes improvements in air quality (SDG targets 3.9.1,7.1.2,and 11.6.2;https://www.who.int/teams/environment-climate-change-and-health/airquality-and-health/policy-progress/sustainable-developmentgoals-air-pollution).Therefore, to avoid neglecting populations at high latitudes and ensure timely policy implementation for improved air quality, more groundbased PM 2.5 assessments are needed in the Arctic and surrounding regions.
In this study, we installed portable PM 2.5 measurement and meteorological instruments in Qaanaaq, northwestern Greenland, during a short summer period to assess local air quality variations based on PM 2.5 levels.In West Greenland, atmospheric aerosol characteristics, such as number concentrations and compositions are influenced by wind system (Kikuchi et al., 1996).Previous research has highlighted that light-absorbing aerosols, including BC, are significant contributors to snow in Greenland due to biomass burnings (Hegg et al., 2009(Hegg et al., , 2010;;McConnell et al., 2007).Qaanaaq is a small village in northwestern Greenland (Figure S1) with a population of approximately 600 people.Northwestern Greenland, including Qaanaaq, was previously under-monitored (Aoki et al., 2014) and is expected to exhibit evident impacts of global warming, such as changes in temperature and surface mass balance of the ice sheet (Fettweis et al., 2013;Rae et al., 2012).Over the past decade, numerous natural and social science studies have been conducted (Sugiyama et al., 2021) under three national Japanese Arctic projects: GRENE (Green Network of Excellence) Arctic Climate Change Research Project, 2011-2016 (https://www.nipr.ac.jp/grene/e/index.html);ArCS (Arctic Challenge for Sustainability) project, 2015-2020 (https://www.nipr.ac.jp/arcs/e/index.html);and ArCS II (Arctic Challenge for Sustainability II), 2020present (https://www.nipr.ac.jp/arcs2/e/).Extensive research has been conducted in Qaanaaq, as previously mentioned; however, there has been little focus on air quality (ambient air pollution).To our knowledge, this study represents the first assessment of ambient PM 2.5 levels in Qaanaaq.The preliminary results of our research shed light on the PM 2.5 characteristics of the ambient environment in this small Arctic community during the summer.These findings highlight crucial research targets for future studies, particularly in the fields of atmospheric and environmental sciences.

| Study site, equipment, and data treatments
We installed a commercial model of the PM 2.5 measurement system (Tanaka Co., Ltd., Hokkaido, Japan: http:// kktanaka.co.jp/products) on the roof of Qaanaaq Club House (QCH-N; Figure 1a,b) to obtain measurements from July 20, 2022 to August 13, 2022 (Table 1).The commercial model is based on the prototype developed by Yasunari et al. (2022) (the PM 2.5 sensor by Nakayama et al. (2018) for the system must be obtained separately), to which some major updates were made, including a waterproof fan (T-MDP825-24L-G; Oriental Motor, Co., Ltd., Tokyo, Japan: https://www.orientalmotor.co.jp/ja/ products/detail?hinmei=T-MDP825-24L-G), and the addition of rain covers (elbows), a converter, handle, and outdoor paint to the insulation box.The air inlet and outlet of the measurement system were placed on the sea and Qaanaaq Ice Cap (QIC) sides, respectively (Figure 1b and Table 1).The threshold temperature of the inbuilt heating system was set to 5 C, as also similarly set by Yasunari et al. (2022).To confirm the functioning of the heating system, we measured the internal temperature at 10-s intervals using an Ondotori TR-74Ui-S (Table S1), which also measured internal relative humidity.PM 2.5 data were also recorded at 10-s intervals.We calculated and obtained the PM 2.5 mass concentrations after multiplying the coefficient of 1.3 by the raw measured data, as suggested by Nakayama et al. (2018).Hourly mean data were calculated when 80% of the raw data were collected for each targeted hour.We used the hourly mean data from both the Kestrel and Ondotori instruments for analysis.
We installed a Kestrel 5500 Weather Meter (Table S2) at 1.2 m above the ground in the yard on the southwest side of QCH-N on July 25 to measure ambient air temperature, relative humidity, atmospheric pressure, wind direction, and wind speed at 1-min intervals.Weather observations by the Kestrel system started at 10:05 p.m. on July 20, and the measurements were taken until 8:05 p.m. on July 25 at a place where the instrument could avoid rainfall (different from the location shown in Table S2).However, overall measurement items at the location during the above period might have been considerably affected by the structure and human activities.Therefore, Kestrel weather data before 8:05 p.m. on July 25 were excluded from the analysis.As wind speed and direction still could have been affected by the proximity of the Kestrel instrument to the QCH-N, we also compared our wind data with mean wind speed and direction data (10 min collected before the target hour and 10-degree intervals in wind direction: Qaanaaq AFIS, 2023, personal communication) recorded at Qaanaaq Airport (APT), located approximately 4 km northwest of QCH-N (Figure S1).The wind data for APT (available in SYNOP data format; station name: Mittarfik Qaanaaq; also see Jensen, 2022) was made available through the Integrated Surface Database (ISD) of the National Oceanic and Atmospheric Administration's (NOAA) National Centers for Environmental Information (NCEI) (NOAA/ NCEI, 2001).The acquired ISD data were collected from 00:00:01 on July 20, 2022 to 00:00:01 on August 14, 2022 (LST); missing or erroneous data were removed based on the ISD quality code.
We used Welch's t-test with SciPy (version 1.6.2) in Python 3 (version 3.8.8) to judge the statistical significance of the mean differences.

| MERRA-2 analyses of aerosols and PM 2.5
To examine the contribution of aerosols transported from remote sources to local air quality, we used the hourly means of NASA's Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2; https://gmao.gsfc.nasa.gov/reanalysis/MERRA-2/)reanalysis data (Table 1).The data assimilation of satellite and in-situ measurements of aerosol optical depth allows MERRA-2 to accurately reproduce atmospheric aerosol (dust, BC, OC, sea salt, and sulfate) distribution (Buchard et al., 2017;Randles et al., 2017).The time series for the MERRA-2 aerosol data was extracted for the grid cell nearest to the QCH-N (Table 1).However, the corresponding grid cell of the MERRA-2 data includes both the QCH-N and APT locations because of the horizontal resolution.The hourly mean PM 2.5 data were calculated using eq. 1 of Buchard et al. (2016), in which they sum up the surface mass concentrations of five aerosol components, with OC treated as particulate organic matter (POM) and sulfate as ammonium sulfate.The analysis was similar to Figure 1 of Yasunari et al. (2021), except for the hourly mean time-series data covering the measurement period.

| Calculating air mass origins and relative deposition distributions of PM 2.5
To discuss the air mass origins of PM 2.5 and its possible deposition distributions, we performed 3-day (72 h) backward trajectory and forward dispersion analyses using the NOAA's HYSPLIT model (online) with the archived global GFS data in 0.25-degree horizontal resolution (https://www.ready.noaa.gov/HYSPLIT.php)(Rolph et al., 2017;Stein et al., 2015).The backward trajectories (ensemble trajectories) were started from each focused start time (see Section 3) at the QCH-N location (Table 1; Figure S1) at 50 m above ground level (a.g.l.).The forward dispersion calculations for 3.5 days (84 h) were started from the waste dump site (DS) in Qaanaaq (Figure S1) because of the maximum total duration of the HYSPLIT forward dispersion (84 h) and the reason mentioned in Section 3.2.We used one mass quantity and set a dispersion height of 0-50 m a.g.l.In addition, the dispersion calculations were implemented with three different dry deposition velocities of 0.0003 (based on Emerson et al., 2018, expecting BC dry deposition velocity), 0.001, and 0.01 m s À1 , respectively (covering the different sizes and characters of emitted particles) to make the discussion of the particle deposition patterns robust.

| RESULTS AND DISCUSSION
3.1 | Characteristics of PM 2.5 and meteorological measurements in Qaanaaq in the summer of 2022 We observed several events of increased PM 2.5 mass concentrations (Figure 2).Although the hourly mean PM 2.5 was 0.0-21.4μg m À3 , the maximum mass concentration in the 10 Às interval data reached 120.9 μg m À3 and exceeded 25 μg m À3 at multiple points.Except for these PM 2.5 -increased events, the background mass concentration levels of PM 2.5 were relatively low in late July compared with those in August.The maximum mass concentration fluctuated more within each hour than the hourly mean data.In August, the maximum concentration within each hour and the background concentration gradually increased with time.The period of greatest pollution was observed between August 8 and 13, suggesting continuous air pollution during this period.We mainly focused on the highly increased PM 2.5 events in August F I G U R E 2 Variations in PM 2.5 at QCH-N from July 20 to August 13, 2022.Black and red lines denote the hourly mean data, calculated if raw data were available for more than 80% of each hour, and the maximum PM 2.5 mass concentration per hour, respectively.Bars shaded in light gray and gray denote periods with no PM 2.5 measurement or those with <80% data available (i.e., "missing"), respectively.
F I G U R E 3 (a) Variations in hourly mean meteorological and PM 2.5 data and (b) Windrose diagram.Temperature data in red and black were measured using the Kestrel (outside) and Ondotori instruments (inside the PM 2.5 measurement system), respectively.Similarly, the blue and black lines indicate relative humidity (RH) measured by the Kestrel (outside) and Ondotori instruments (inside the measurement system), respectively.Pressure relates to sea level pressure.Wind speeds and directions shown in purple lines and yellow dots correspond to QCH-N (QCH), while those in dark blue lines and brown dots correspond to Qaanaaq Airport (APT).The hourly mean PM 2.5 data are similar to those represented by the black line in Figure 2. Except for the data measured by the Ondotori and PM 2.5 measurement systems and those obtained from APT, the Kestrel instrument measured all the other data.See more detailed information on the Ondotori and Kestrel measurements in Tables S1 and S2.
in the following sections; the other PM 2.5 characteristics in July were mentioned in the SI Text as additional cases, also mentioning Figure 1c,d.
Air temperatures were consistently higher than the freezing point (Figure 3a).Unfortunately, meteorological data measured by the Kestrel instrument were only available from approximately July 26.Variations in temperature and relative humidity were strongly correlated between the inside and outside of the PM 2.5 measurement system, indicating that variations in these variables both inside and outside the PM 2.5 measurement system were consistent with each other, except when the internal temperature of the system was below the set threshold (5 C, see Section 2.1).When the outside temperature was close to freezing (July 28 to 29 and August 5 to 6), the temperature differences between the inside and outside of the PM 2.5 measurement system indicated that the internal heating system worked properly.Although Yasunari et al. (2022) confirmed the performance of the heating system at À25 C, our results also verified the functioning of the heating system under ambient air conditions in Greenland.Other characteristics of air temperature and relative humidity are summarized in the SI Text.
The atmospheric pressure variations from July 25 onward were relatively stable compared with the other meteorological variables (Figure 3a).The relatively high pressure continued until August 3, following which it tended to decrease.The diurnal cycles of wind speed at both APT and QCH-N were clear (Figure 3a).However, the wind speed at QCH-N was lower than that at the airport (Figure 3a).The wind direction at QCH-N was mainly from the North-Northeast, which is from the DS direction, and also more stable than that at the airport (Figure 3b).This unusual behavior of the wind measured by the Kestrel instrument implies that wind speed and direction at QCH-N were probably affected by the building, as mentioned in Section 2.1.The prevailing winds at APT were primarily from West and North-West, mainly from the seaside direction (Figure 3b).Considering the geographical location of QCH-N (Figure S1) and the prevailing westerly winds at APT (Figure 3b), the PM 2.5 measurement system installed at QCH-N (Figure 1b) is also likely affected by the main wind directions from the sea.
The wind directions at APT around the peak wind speed in the diurnal cycles were often $270 (i.e., westerly winds from the sea) (Figure 3a,b).Some outlier days of strong wind speeds were observed on July 22 and 23 and August 8, 9, 12, and 13, corresponding to low-pressure events.On these days, wind directions were often <135 (Figure 3a,b) (i.e., southeasterly winds originating inland, for example, from the QIC and Greenland ice sheet; Figure S1).Although wind directions are associated with the PM 2.5 increases, as in Figure 3, it is also worth noting that higher PM 2.5 mass concentrations tended to be observed on strong-wind days compared to weak-wind days.

| Open waste burning and its impact on local air quality and possible depositions over the nearby sea
As shown in Figure 2, continuous air pollution was observed from August 8.Clear peaks in daily and hourly PM 2.5 concentrations were observed with elevated surface pollutant levels and strong diurnal variations (Figure 4).Each day, the 75th percentile of the PM 2.5 data was lower than 10 μg m À3 .The highest hourly mean PM 2.5 was observed on August 12.We observed three poor air quality periods (Figure 4b): (1) three successive days from July 20 to 22; (2) a single day on July 27; (3) and five consecutive days from August 8 to 12. Most of the air pollution was observed in the afternoon (Figure 4c), especially during the first and third periods (Figure 4a).Air pollution for the second period was concentrated between 5:00 and 7:00 a.m.(Figure 4a).During the third period of air pollution starting from August 8, air quality was relatively better in the early morning and nighttime from August 9 to 12; however, ambient air pollution was the worst on August 12, during which air quality continuously deteriorated from before noon to the late evening (approximately 11:00 p.m. to 0:00 a.m.) (Figure 4a).Therefore, our subsequent analysis focused on the most prolonged third air pollution period.
On August 8, we observed clear black smoke from the waste DS in Qaanaaq (Figures 1e,5,S1,and S3), located between APT and QCH-N (also the center of Qaanaaq) (Figure S1).Videos of the air pollution event were taken at five locations from QCH-N walking toward the DS (Figure S3 and Videos S1-S5).Black smoke was dispersed with considerable heterogeneity but nevertheless covered a wide area over Qaanaaq (Figure 5a,b).Furthermore, although the intensity of the smoke was low, we could still confirm the emission of smoke from the DS on August 11 (Figure 1f), implying that open waste burning continues for at least a few days.
To discuss the cause of the increased PM 2.5 in Qaanaaq on August 8 (Figures 2 and 4), we also assessed the contributions of aerosols from remote origins outside  b) and (c) were statistically analyzed without regard to the ratio of unmeasured or missing periods.Therefore, each daily or hourly statistic calculated with a missing rate exceeding 20% is presented with a cross mark.
MERRA-2 showed low hourly mean PM 2.5 mass concentrations from July 20 to August 14 (Figure 6).However, some increases were observed on July 20 to 22, with a maximum of 2.67 μg m À3 , which was still relatively very low.We did not observe any distinct increases in PM 2.5 concentrations in the MERRA-2 data on or around August 8.
The MERRA-2 aerosol data are produced based on the aerosols simulated by a global model, also considering the data assimilation method with satellite-observed aerosol optical depth (AOD) data from MODIS and MISR instruments but not from VIIRS (Randles et al., 2017).
However, the MODIS AOD failed to detect fires in northwest Greenland on August 8 (Table S3; https://firms.modaps.eosdis.nasa.gov/map/#m:advanced;d:2022-08-08;@-67.4,76.5,7.0z).These results imply that the MERRA-2 data did not include local fire-related aerosol emissions.Furthermore, persistently low MERRA-2-based PM 2.5 mass concentrations at the grid near Qaanaaq suggest that the aerosol contributions from remote regions to the observed PM 2.5 from August 8 to 13 were minimal.
Our additional analyses further suggested that most of the high PM 2.5 events occurred due to local air pollution, as confirmed by the following: (1) the main air mass origins of the top five increased PM 2.5 were either from the sea nearby Qaanaaq or from the inland of Greenland (Figure S5); (2) the correlation between the calculated hourly mean MERRA-2 PM 2.5 and the observed hourly mean PM 2.5 data were extremely low, suggesting the sources increasing PM 2.5 in the observation were not considered in the MERRA-2 data (i.e., local emission sources) (Figure S6).
Based on the MERRA-2 and HYSPLIT results with photo and video evidence (Figure 5 and Videos S1), we conclude that the increased PM 2.5 mass concentrations from August 8 were caused by the local open waste burning at the DS.
To further assess the possibility of the relative contributions of the emitted PM 2.5 -sized aerosols from the open waste burning to the surrounding areas of Greenland as aerosol depositions, we also ran the NOAA's HYSPLIT model for forward dispersion calculations (see Section 2.3).Based on Figures 4 and 5a, we assumed the continuity of the open waste burning to be at least 3.5 days within the maximum total release duration (84 h = 3.5 days) in the HYSPLIT setting (see Section 2.3).We started the dispersion calculations at 11:57 UTC, August 8, with three different dry deposition velocities covering various particulate nature and size characteristics.In any of the three cases, the accumulated relative deposition patterns looked similar (Figure S7), in which most of the aerosol depositions were concentrated in the sea around Qaanaaq, including Baffin Bay.In the observed PM 2.5 (Figures 4 and 5), we can consider the continuity of the open waste burning for up to 4.5 days.However, due to the limitation of the model setting, we could only consider a total particle release duration of 3.5 days.Therefore, more continuous depositions than our estimated depositions were expected.These deposition patterns imply some possible aerosol depositions from the open waste burning in Qaanaaq to the sea surface in the surrounding areas and raise future scientific research targets on the impacts of local aerosol emissions from Greenland to the nearby ocean.
"The incineration plant in Qaanaaq was out of operation from 2012 to 2022.That is why they had open burnings with the Greenland government's permission.After that, the burnings outside stopped, and the waste burnings have been carried out generally once a week at the incineration facility in Qaanaaq (a house with a chimney called Forbraendingsanlaeg)" (Karen M. Gadegaard, 2023, personal communication).
Therefore, no more open waste burning, as observed in the present study in Qaanaaq (Figure 5c), is likely to be conducted.However, the impact of smoke from the incineration facility on local ambient air quality, particularly in terms of increasing local PM 2.5 levels, remains unknown due to a lack of scientific data.Although we captured the open waste burning impact on air quality, this study limits the only short period in the summer of 2022.To fully capture the seasonal characteristics of PM 2.5 in Qaanaaq, and to assess and ensure healthy air quality for the local people, long-term PM 2.5 measurements are necessary in the future.

| SUMMARY AND CONCLUSIONS
In this study, we measured PM 2.5 mass concentrations using a commercial PM 2.5 measurement system, updated from the developed prototype by Yasunari et al. (2022), along with meteorological data collected using Kestrel and Ondotori instruments at Qaanaaq, Greenland, from July 20 to August 13, 2022.To the best of our knowledge, this study is the first to report continuous ambient PM 2.5 (i.e., air quality) measurements in Qaanaaq, Greenland.
On August 8, 2022, we observed clear black smoke from open waste burning at the DS, corresponding to consistently high PM 2.5 mass concentrations.We confirmed that the increased PM 2.5 mass concentrations from August 8 were caused by smoke emitted from local open waste burning in Qaanaaq using NASA's MERRA-2 reanalysis data (aerosol and calculated PM 2.5 , including comparison with measured PM 2.5 ), NOAA's HYSPLIT backward trajectories, and meteorological data.Transboundary air pollution was minimal during our measurement period, although MERRA-2 data suggests that some minor contributions from biomass burning outside Greenland were plausible.Consequently, most high PM 2.5 events were likely linked to local pollution sources.Despite the observed hourly mean PM 2.5 mass concentrations not being alarmingly high during the measurement period, potential contributions of aerosol depositions from open waste burning to the nearby sea were indicated by HYSPLIT forward dispersion analyses.Therefore, it is noteworthy that even a single local air pollution source in the Arctic can potentially impact surrounding areas, making it an important focus for future research.
Although open waste burning in Qaanaaq ceased in 2022 with the operation of the incineration plant (see Section 3.2), to fully identify local sources of discrete air pollution in greater detail and maintain good air quality, including the seasonal characteristics of air pollution, future studies should continuously obtain more air quality-related observations in this area, including the detection of specific chemical components (e.g., BC and OC measurement).Furthermore, implementing more PM 2.5 measurements at different locations in Qaanaaq would assist in determining spatiotemporal variations.Moreover, recording the incineration facility's operations for monitoring air quality would be helpful.
To promote the health of Arctic residents in terms of atmospheric air quality, large-scale and long-term measurements of PM 2.5 and other atmospheric chemicals are needed.These air quality measurements should also be required to satisfy the "no-one-left-behind" policy (https://sdgs.un.org/2030agenda) of the SDG in the Arctic regarding air quality.
Globally, PM 2.5 emissions from open waste burning constitute 29% of total anthropogenic emissions and are linked to an estimated 270,000 premature adult deaths annually due to chronic exposure (Kodros et al., 2016;Wiedinmyer et al., 2014).In the Arctic, including Greenland, communities are often small, remote, and isolated, making waste disposal costly and challenging.Consequently, waste is sometimes disposed of through open dumping or open burning (Aliabadi et al., 2015;Burns et al., 2021;Eisted & Christensen, 2011;Schmale et al., 2018).Waste burning considerably impacts air quality in the Arctic, affecting human health (Schmale et al., 2018).Monitoring environmental treatment at incinerators and dump sites in Greenland is limited, raising concerns about air, soil, and water pollution, particularly since treatment facilities are often located near residential areas (Eisted & Christensen, 2011).Open waste burning increases atmospheric BC and PM 2.5 in the nearby areas, but there is substantial uncertainty regarding its emission characteristics and chemical composition due to variability in combustion modes and waste materials (Cheng et al., 2020;Krecl et al., 2021).In Qaanaaq, smoke emissions from the incineration facility will still be likely observed (see Section 3.2) despite the cessation of open waste burning.As shown in Figure S7, aerosol depositions in the surrounding areas of Qaanaaq are possible when smoke emissions occur.Therefore, aerosol depositions, such as OC and BC, in the nearby sea and over the snow surface of Greenland should be important research targets to in future studies.Additionally, the proximity of Qaanaaq to the QIC and the Greenland ice sheet raises concerns about reduced albedo due to the snow-darkening effect of BC deposition, a welldocumented environmental issue (IPCC, 2019(IPCC, , 2021;;Qian et al., 2015;Warren & Wiscombe, 1980;Yasunari et al., 2011Yasunari et al., , 2014Yasunari et al., , 2015)).The deposition of BC from Canadian wildfires in snow in northwestern Greenland has also been discussed (Thomas et al., 2017).Therefore, more comprehensive air quality measurements and local air pollution source identification are needed in future studies.

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I G U R E 1 Installation site of PM 2.5 monitor and various PM 2.5 sources: (a) PM 2.5 monitor at QCH-N (seen from the southwest).(b) View of the inlet side of PM 2.5 monitor.(c) Cruise ship approaching Qaanaaq village (08:05:01 on July 27, 2022).(d) Refueling truck (14:49:01 on July 28, 2022).(e) Open waste burning (15:05:01 on August 8, 2022).The smoke from the dump site (DS) drifts toward the Qaanaaq Ice Cap (QIC) and up toward the mountain.(f) Three days following open waste burning (16:01:01 on August 11, 2022).The smoke subsided compared with that on August 8, 2022.The time of the images corresponds to the local time in Qaanaaq, Greenland.

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I G U R E 4 Distribution of daily and hourly visual statistics of PM 2.5 mass concentration during July and August 2022: (a) Matrix map of the hourly mean PM 2.5 mass concentrations.(b) Daily statistics.(c) Hourly statistics.Note that the data in (

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I G U R E 5 Open waste burning at the DS in Qaanaaq on August 8, 2022: (a) 09:57:01 near the QCH-N; (b) 10:01:01 from the QCH-N; (c) 10:12:01 near the DS.The time the photos were taken corresponds to local time in Qaanaaq.F I G U R E 6 Time-series of PM 2.5 and percentage of each aerosol component around Qaanaaq, Greenland, based on the MERRA-2 re-analysis data.The data are based on the hourly mean MERRA-2 data.
Study site and description of PM 2.5 measurement.
T A B L E 1