Industrial emissions are an additional source of hydrocarbons in the megacity of São Paulo

Authors: Monique Silva Coelho and Pamela Dominutti

Non-methane hydrocarbons (NMHCs) can be emitted directly into the atmosphere by a wide range of anthropogenic and natural sources (Seinfeld and Pandis, 2006). However, in urban areas, they are mainly released by anthropogenic sources, such as vehicle exhausts, fuel evaporation, solvent use, emissions of natural gas, and industrial processes (Friedrich and Obermeier, 1999). Despite presenting low concentrations in the atmosphere (mixing ratios ranging from few parts per trillion (pptv) to a few ten parts per billion (ppbv)), some of these compounds can exert a detrimental effect on human health, affecting the respiratory system and, in some cases, provoking depressing central nervous system, besides the carcinogenic effect (Kansal, 2009; NTP, 2016).

Once released into the atmosphere, primary NMHCs undergo chemical transformations, mainly due to the presence of the OH radical during the day. NMHCs have a fundamental role in the oxidizing capacity of the atmosphere due to the production of secondary pollutants, such as secondary organic aerosols (SOA), and tropospheric ozone (O3) (Seinfeld and Pandis, 2006).

Previous studies developed at the Metropolitan Area of São Paulo (MASP), mainly associated NMHCs to traffic emissions and higher concentrations were observed during the rush hours. However, there are no previous studies evaluating these compounds at industrial areas in the MASP. According to the estimation made by Environmental Agency of the State of São Paulo (CETESB), the MASP has 687 industries that emitted carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), particles (PM) and sulfur oxides (SOx) (CETESB, 2019).

Petrochemical and Industrial Complex (PIC). Author: ABC do ABC (2017).

The Great ABC region, located in the southeast of MASP, is a densely populated urban area and is characterized by industrial activities, starting with the opening of an oil refinery in 1954 and followed by the expansion of the Petrochemical and Industrial Complex (PIC). This industrial complex is composed by an oil refinery and 14 industries, which produce ethylene, propylene, and polyethylene from the distillation of naphtha, as well as fertilizers and other chemical products, to supply the MASP industries (the largest consumer market in South America, with great economic importance in Brazil).

A recent study has provided a detailed analysis of 35 NMHCs measured in the PIC area for the first time (Coelho et al., 2021). Measurements of NMHCs species include alkanes (C6-C11), aromatics (C6-C10), and alkenes (cis/trans-2-hexene).

The field campaign developed in 2016 and 2017, depicted that the most abundant compounds near PIC were toluene (1.5 ± 1.1 ppbv), cis-2-hexene (1.4 ± 1.9 ppbv), benzene (0.55 ± 0.66 ppbv), and m+p-xylene (0.58 ± 0.3 ppbv). Furthermore, the observations showed higher NMHCs concentrations at BTP (industrial site) than the UFABC site (traffic), by a factor of 2. Among them, the most abundant HCs were aromatics (56 to 58%).

BTEX mixing ratios observed at the industrial (PIC) and traffic (UFABC) sites and their potential reactions and impacts in the troposphere (Coelho et al., 2021).

The evaluation of correlations and ratios of BTEX showed that in addition to the industrial influence around PIC, vehicular emissions were also observed. The comparison with other industrial areas worldwide showed a good agreement in the NMHCs profile with Japan and the USA, suggesting the presence of similar emission sources (Tiwari et al., 2010; Leuchner and Rappenglück, 2010).

About the impacts caused by these emissions, the potential formation of secondary pollutants presented higher values at the industrial site than the traffic site. The lifetime cancer risk value calculated for the industrial site was six times higher than the value recommended by US EPA, indicating a probable cancer risk due to exposure to benzene for people who live, work, or circulate daily on the Great ABC region, especially in the vicinity of the PIC. Furthermore, frequent exceedances of World Health Organization (WHO, 2018) guidelines for ozone and PM2.5 have been commonly observed in the PIC area.

Emission control strategies were applied in the last years in the MASP, that implied in a decrease of NMHCs, and other pollutant concentrations related to traffic emissions. Nevertheless, little is known about industrial sources and their emissions in this area. Even though the governmental local inventories consider the emissions from industrial activities, a lack of industrial profile and activities is observed. Therefore, more details about speciation profiles are needed to improve the representation of industrial emissions in inventories and to better estimate their effects on the atmosphere. Thus, in a global context where vehicular emissions are decreasing over the last decades, additional efforts are necessary to evaluate other sources of air pollution and their implications on the air quality degradation of the megacity of São Paulo.

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