Particulate matter in the atmosphere, especially when sized 2.5 and 10 micrometres, has received attention from researchers. Recent research correlates elemental carbon, which can carry a wide variety of toxic chemicals, with cardio-respiratory hospitalisations, preterm births and mortality. But how is elemental carbon deposited in the human respiratory system?
Since 2010, Sayantan Sarkar, IISER Kolkata has been working on the effects of ambient particulate matter on humans. Now he collaborates with researchers in China and Singapore to comprehensively evaluate the potential health impacts of exposure to elemental carbon.
The team selected Guangzhou, a large industrialized region in China. Guangzhou is highly populated with a high volume of vehicular traffic. So, residents are exposed to elemental carbon.
The scientists set up a sampling instrument, a six-stage high flow impactor, on the roof of a fourteen-floor building in urban Guangzhou to assess how seasonality and haze – where dust, smoke, and other dry particulates obscure the sky – affect exposure to elemental carbon.
They checked size-segregated deposition of elemental carbon in the sampling instrument: about 64 per cent was fine particles and 36 per cent was coarse particles. A large fraction was in droplet mode indicating that most elemental carbon particles had undergone atmospheric modification.
The researchers found that the concentration of elemental carbon was significantly higher during the dry season than it was during the wet season. Haze enhanced elemental carbon levels in both seasons. This may be due to the movement of air masses – from other cities during the dry season and from oceans during the wet season – suggest the scientists.
To investigate how elemental carbon is deposited in the respiratory system, the researchers used a particle dosimetry model. Such a model makes it easy to calculate regional and site-specific deposition as well as the clearance of particles, without using human volunteers.
The researchers populated the model with data on size-segregated aerosols. They found that the concentration of elemental carbon deposited in the human respiratory tract was about 40 per cent of the total ambient elemental carbon. Nearly half is deposited in the head region of the respiratory system. Nearly a quarter reaches the tracheobronchial region.
The team found that the total elemental carbon deposition was higher for infants and children. This makes them more vulnerable to air pollution.
The researchers say that breathing through both mouth and nose is associated with lower total deposition while nasal breathing leads to lower deposition in the tracheobronchial and pulmonary regions. The amount of elemental carbon deposited increases with breathing rate. So there is a greater risk in outdoor physical activity when the air is polluted.
‘All these factors need to be taken into account when we evaluate the impact of elemental carbon on health’, says Sarkar, IISER Kolkata.
Sileesh Mullasseri, KUFOS