Measurement of PM 2.5 and PM 10 Concentrations in Nakhodka City with a Network of Automatic Monitoring Stations

The Nakhodka city—Port Vostochny urban agglomeration is Russia’s largest transport hub on the Pacific Ocean. Within Nakhodka city, there are several marine terminals involved in coal handling and shipment. An increase in coal handling leads to environmental pollution and an impact on public health. This work focuses on the concentrations of PM 2.5 and PM 10 in the air of Nakhodka city during the period from January to May 2021. PM concentrations were measured using a network of automatic monitoring stations deployed in 5 districts of Nakhodka city. Data on PM 2.5 and PM 10 concentrations were averaged by months. According to the results obtained, the highest concentrations of PM 10 and PM 2.5 were observed in the winter months, and then there was a gradual decrease in concentrations at all observation points. Elevated concentrations of particulate matter were observed to the north of the Nakhodka port, which is due to the proximity to the port infrastructure and the railroad, as well as in the central part of the city. Given the specific conditions of occurrence and transport of suspended particles in the atmosphere of Nakhodka city, they can be hazardous to public health.


INTRODUCTION
Air pollution is a pressing problem in modern cities.One of the main factors in air pollution is fine particulate matter (PM) that can penetrate the human respiratory tract.Exposure to PM is associated with the increased risk for respiratory diseases morbidity (Kim et al., 2018;Yamagishi et al., 2020), cardiac-associated morbidity and mortality (Pelucchi et al., 2009;Sadeghi et al., 2015), and increased risk for viral respiratory infections (Adams et al., 2015;Cruz et al., 2015;Tsatsakis et al., 2020).
Automobile traffic and industrial activities (including power generation) are named as the main anthropogenic sources of PM in the atmosphere of cities (Karagulian et al., 2015).Industrial activities specific for port cities involve handling and shipment of loose goods, including coal.In this study, we will focus on PM associated with coal handling operations in one of the port cities in the Russian Far East.
The Nakhodka city-Port Vostochny urban agglomeration is Russia's largest transport hub on the Pacific Ocean.Within Nakhodka city, there are several marine terminals involved in coal handling and shipment.According to official data, coal cargo turnover in 2020 was 1,684.5 thousand tons in Nakhodka port (3.5% higher than in 2019), and 36,910.9thousand tons in Vostochny port (5.8% higher than in 2019) (Report on the environmental situation in Primorsky Krai, 2021).Over the past few years, the air pollution problem in Nakhodka city has been receiving a lot of attention from researchers and the public.An increase in coal handling leads to environmental pollution and an impact on public health.Coal dust from coal mining, transshipment, and processing is the strongest air pollutant, triggering a range of respiratory diseases (Petsonk et al., 2013;Laney and Weissman, 2014).
According to the data of the Russian consumer protection agency, among all samples of total suspended particles (TSP) collected in 2017 in the Primorsky Krai, the highest percentage of samples exceeding the maximum permissible TSP levels was registered in Nakhodka city (8.5% of all samples).This fact was attributed to coal handling operations in Nakhodka port complex (Report on the environmental situation in Primorsky Krai, 2018).According to updated monitoring data obtained in 2020, there was a 1.6% decrease in air pollution with TSP in Nakhodka during coal handling operations.In 2021, the air pollution level in Nakhodka calculated by the Composite Pollution Index (CPI) was rated as "low" (Report on the environmental situation in Primorsky Krai, 2021).While official data claims that the air pollution levels in the city are decreasing, there is a need for independent monitoring of air pollution associated with coal handling operations.
To date, there is very little reliable data on the quantitative and qualitative characteristics of coal dust microparticles in the air near coal terminals in the cities of the Russian Far East.Taking into account the growing anthropogenic pressure in industrial cities, it is necessary to take practical steps towards solving the environmental pollution issues, including pollution with coal dust.This work continues a series of studies on the environmental impact of coal handling in ports (Kirichenko et al., 2017(Kirichenko et al., , 2019(Kirichenko et al., , 2021)).The goal of this work was to determine the variations in the content of PM in the air of a city with large-scale coal shipment and handling operations.
For the study, automatic monitoring stations were constructed that measured several atmospheric air parameters in real-time.A network of monitoring stations was deployed in 5 locations in Nakhodka city.The concentrations of PM2.5 and PM10 were chosen as priority parameters for pollution assessment in this study.

METHODS
Measurements were taken using a network of automatic monitoring stations deployed in 5 areas in Nakhodka city.Parameters measured by the monitoring stations included: -Temperature, degree Celsius (accuracy ± 0.1°); -Relative humidity: 10-90% (accuracy ± 2%); -Particulate matter concentrations: PM2.5, PM10 (0.0-999.9 µg m -3 ), measuring step 0.3 µg m -3 , (accuracy ± 15%) -Wind direction and speed: 0-50 m s -1 , measuring step 0.1 m s -1 (accuracy ± 1 m s -1 ).Data from automatic monitoring stations (averaged for 10 min) are transmitted via GSM/GPRS/EDGE/2G/3G communication channels to a remote FTP/HTML server 1-2 times a day.The files can be accessed from any location with an Internet connection.The monitoring devices are stationary, with a power supply of 220 V mains.In case of mains power failure, stations operate autonomously for up to 2 days.The stations are made according to IP67 standard, the operating temperature range is -0 to +50 deg.C. The assembled monitoring station is a "tower" consisting of monitoring sensors and a control unit mounted on a tripod (Fig. 1).
A network of automatic monitoring stations was deployed in different parts of Nakhodka city.The locations for monitoring stations represent residential and industrial areas.They were chosen based on the proximity to port infrastructure and prevailing wind directions (easterly, northwesterly).Observation point No. 1 is located on a hill above the port infrastructure that includes coal-handling facilities and railroad.There are several heat sources in the observation area.Automobile traffic intensity is low.Point No. 2 is located in a residential area on the roof of a 6-story building.With a shopping mall nearby, automobile traffic is sometimes intense in this area.Monitoring station No. 3 was deployed in a quarter of single-family homes.In winter, these

RESULTS AND DISCUSSION
Data on PM2.5 and PM10 concentrations were averaged by months.The concentrations of both measured PM fractions were highest in the winter months (January and February), and then there was a gradual decrease (Fig. 3, Table 1).
Monitoring stations located at Points No. 4 and No. 5 recorded PM2.5 concentrations at 21.7 and 24.6 µg m -3 , respectively, during the winter months.The highest average concentration of PM2.5 for the period January-May 2021 was registered at point No. 5 at 17.2 µg m -3 .These values do not exceed the threshold levels specified in the Russian and US standards (24-hour concentration-35 µg m -3 ; annual concentration-25 µg m -3 , according to the Russian standard) (U.S. EPA, 2020;  and they have been observed there before (Kirichenko et al., 2019(Kirichenko et al., , 2021)).High concentrations of PM10 at point No. 3, separated from the main part of the city by hills, can be associated with the natural background of the territory, as well as dust from the local dirt roads.The lowest average concentrations of particulate matter were observed at the measurement points located to the south of the port infrastructure (Krabovaya St. and Sportivnaya St.).The gradual decrease in particle concentrations in the spring compared to the winter months (January and February) can be explained by decreasing heat and power generation due to warmer outdoor temperatures.Another reason may be an increase in average humidity with warmer days.Moisture binds suspended particles and facilitates their deposition to the surface with precipitation.
When comparing the data, it should be taken into account that particulate matter with an aerodynamic diameter of 2.5 and 10 micrometers (PM2.5 and PM10) can have very different chemical composition, structure, concentration, sources of origin, and exposure levels.The authors of a large-scale review devoted to PM particle pollution in cities of 51 countries (Karagulian et al., 2015) provide data on the average contribution of sources of PM particles into the atmosphere (Table 2).
Urban dust is largely formed by emissions from motor vehicles.The hazard of emissions of harmful substances from motor vehicles is exacerbated by the fact that the emissions are released in the surface layer directly near the human respiratory organs.The composition of microparticles of automobile exhaust includes soot, ash, mineral particles, as well as heavy metals that are both free and in the sorbed form on the surface of soot and ash particles: V, Cr, Al, P, Mn, Ni, K, Sr, Cd, Cu, Fe, Zn, Na, Ba, Zr, etc. (Pant and Harrison, 2013;Chernyshev et al., 2018;Gope et al., 2018).
Coal dust, which is specific to coal handling areas, contains heavy metals (Pb, Cr, Cd, Ni, Cu, Co, Zn, etc.) that have toxic effects on the human body (Ishtiaq et al., 2018).Thus, the measured average concentrations of PM2.5 and PM10 from January to May 2021 did not exceed values of maximum permissible levels outlined in the Russian and US standards, but in some cases were close to their threshold values.Given the specific conditions of occurrence and transport of suspended particles in the atmosphere of Nakhodka city, they are hazardous to public health.

CONCLUSIONS
According to the averaged data on particulate matter concentrations in the air of Nakhodka city, the highest PM10 and PM2.5 concentrations were observed in the winter months (January and February), followed by a gradual decline in concentrations at all observation sites.High concentrations of particulate matter were observed to the north of the Nakhodka city port, which is associated with the proximity to the port infrastructure and the railroad, which is used to transport coal wagons for subsequent transshipment at coal terminals.Elevated concentrations of particulate matter at a distance from coal terminals, in the central part of the city, may be caused by vehicle emissions.High PM10 concentrations at the background point separated from the main part of the city by hills can be attributed to the natural background of the territory, as well as dusting from the local dirt roads.
In general, the measured average concentrations of PM2.5 and PM10 particles did not exceed the maximum permissible concentrations, but in some cases approached their threshold values.According to the official statistical data, there is a gradual reduction of air pollution with airborne PM in Nakhodka city.Coal dust affects areas directly adjacent to the port.PM sources in other districts are mainly heat-and power generation and traffic.Nevertheless, air pollution associated with industrial activities needs to be continually studied and monitored.The next logical step for this study would be to model the distribution patterns of PM and carry out toxicological experiments with coal particles.

Fig. 2 .
Fig. 2. Location of the study area and placement of automatic monitoring stations in Nakhodka city.

Fig. 3 .
Fig. 3. Mean concentrations of PM2.5 and PM10 in Nakhodka city from January to May 2021 measured by the monitoring stations.

Table 1 .
Comparison of PM2.5 and PM10 concentrations in Nakhodka city in January-May 2021 with the US and Russian standards.