2.1. Study area

Meycauayan city, Bulacan is about nineteen (19) kilometers north of Manila and about 22 km south of Malolos city, the capital city of the province of Bulacan (between 14.738° and 14.755° north and between 120.943° and 120.995° east) [10]. It is bounded by the town of Marilao to the north, Valenzuela City to the south, Caloocan City to the east and the town of Obando to the west. Major industries include fine jewelry making, leather products manufacturing and commercial establishments [11]. The province of Bulacan is also considered the biggest producer of used lead acid battery (ULAB) [10]. The neighboring town, Marilao, houses a lead smelting plant owned by the largest lead battery recycler in the country as well as numerous unregulated ULAB plants [10,12].

Leather tanning industries are known emitters of Volatile Organic Compounds (VOCs) and Hazardous Air Pollutants (HAPs). Heavy metal air emissions from tannery operations are chromium (Cr), chromium compounds, manganese (Mn), and Manganese compounds [13,14]. Chromium compounds, identified as one of the HAPs emitted by tanning industries, mainly come from chromium salts, which are the most widely used tanning substance. When emitted into the atmosphere, Cr species are present in the form of particles and droplet aerosols [15]. Occupational exposure to hexavalent chromium compounds has been associated with increased risk of respiratory system cancers [16].

Sampling sites were chosen from eight different barangays in Meycauayan city. The eight barangays are as follows: (AQS1) Barangay Caingin, (AQS2) Barangay Banga, (AQS3) Barangay Calvario, (AQS4) Barangay Camalig, (AQS5) Barangay Langka, (AQS6) Barangay Perez, (AQS7) Barangay Iba and (AQS8) Barangay Malhacan. The barangays were selected to represent the different land classifications according to use whether agricultural, industrial, residential, or just open space. The eight (8) air quality sampling (AQS) locations are shown in Fig. 1 and described in Table 1.

Locations of aerosol sampling (AQS) stations. Land cover measurements of Bulacan were collected from Geoportal [17] and were mapped out using QGIS 3.22.16 [18].

Aerosol sampling point location in Meycauayan city.

The location of AQS1 (Caingin) is a former dumpsite but people continue to throw garbage in the area. There were also people living around this dump site. AQS2 (Banga) is an open space area wherein trucks used for construction are being kept. There are no residences within this area. AQS3 (Calvario) has a public market and an open space wherein some people throw garbage and turn it into a dump site. There are about three to four families living in this area who are caretakers of the land. Flooding is also evident in this area even if the sampling was done during the summer season, which has minimal or no rain at all. AQS4 (Camalig) is identified as agricultural land and there are no industrial buildings in the area. In AQS5 (Langka), there are industries situated along the riverbanks and a residential area as well. AQS6 (Perez) is a purely residential area, the sampling here was done inside a subdivision. AQS7 (Iba) is a purely industrial land where there are factories and warehouses around the sampling site. Lastly, the sampling site AQS8 (Malhacan) is along the roadside. The mentioned barangays are situated along the riverbanks except for barangay Camalig, Iba and Malhacan.