Emissions of aerosols and climate-warming gases from coal-fired brick kilns in South Asia and Colombia

Abstract:

About 1.2 trillion clay bricks (3500 Tg) are fired, annually, and most are fired in small-scale or traditional kilns that burn coal or biomass. Emissions from brick kilns contribute to climate warming, largely due to CO₂. However, unlike many sources, the climate effect of short-lived climate forcers (SLCFs) may also cause warming; some kiln technologies emit so much black carbon (BC) relative to other, cooling, aerosols that there is a net positive short-term climate forcing. BC emission factors from brick kilns can vary by over two orders of magnitude depending on the type of kiln. Thus, converting between a highly emitting or inefficient kiln to one that has low emissions could reduce the pollution from the sector while maintaining the same brick production rate. However, many types of kilns have no or few BC emission factor measurements and, of these, most are short duration snapshots. Here, 24 hour emissions of gases (CO₂, CO, and SO₂) and particles (PM_2.5, organic carbon (OC), elemental carbon (EC), particle scattering, and particle absorption) were measured from a wide range of brick kiln types in South Asia and South America, many of which do not have previous measurements, including clamps, hoffman kilns, Colombian zigzags, coleman, and artisanal kilns. Additionally, this study provides a detailed comparison and uncertainty analysis of two common emission factor calculations, 1) the US Environmental Protection Agency (EPA) stack flow method and 2) the carbon balance method. Considering the 10 continuously fired kilns in this study, the quantified EPA method uncertainties were due to stack flow rate (7-75%), fuel consumption (7-41%), non-simultaneous velocity measurements (8-83%), and short duration tests (20-92% for 3 nonconsecutive 1 hour tests). Uncertainties were greatest in kilns with low (under 1 ms^-1) stack flow rates and batch fired kilns when the full range of the firing is not measured. The carbon balance method is less prone to high uncertainties, but can underestimate the emission factors by 50% or more, if CO₂ emissions from the clay is not accounted for. This is likely a common cause of emission factor underestimation in the current literature.