Analysis of black carbon and carbon monoxide observed over the Indian Ocean: Implications for emissions and photochemistry

Abstract

[1] Air from South Asia carries heavy loadings of organic and light-absorbing aerosol but low concentrations of ozone. We investigate ambient pollutant concentrations measured during the Indian Ocean Experiment (INDOEX), and we estimate emissions to determine the origin, magnitude, and impacts of air pollution from South Asia and to understand better the uncertainty in emission inventories. In India, the preponderance of motorcycles with small, two-stroke engines and the practice of adulterating gasoline with kerosene lead to high CO emission factors; for 1999, we estimate release of 15 Tg yr À1 from fossil fuel use and 40 Tg yr À1 from biomass burning. With the addition of isoprene oxidation, the total CO emissions were 67 Tg yr À1 from India and 87 Tg(CO) yr À1 from all of South Asia. These values indicate a somewhat larger contribution from fossil fuels but slightly lower overall emissions when compared to prior emission inventories. Two-stroke engines also exhibit high emission factors for volatile organic compounds (VOC) and particulate organic matter but produce only modest amounts of NO x . Near sources in India, VOC to NO x ratios appear too high for efficient O 3 formation, although other factors probably contribute to observed low O 3 mixing ratios. An inventory based on source characteristics and known emission factors for black carbon (BC) from South Asia yields 0.7 Tg yr À1 (upper limit of about 1.0 Tg yr À1 ) with biomass burning as the dominant source. We can test this inventory with measurements of ambient CO and BC-ship, island, and aircraft observations of air from South Asia all show a positive correlation between CO and BC (r 2 = 0.71-0.81). Such strong correlations have also been observed over North America and Europe, but with a lower BC/CO slope. Ambient concentrations indicate high BC emission from South Asia: 2-3 Tg(BC) yr À1 . This disagreement with emission inventories demonstrates the need for direct measurements from sources in India.

Characteristics of Black Carbon Aerosol during the Chinese Lunar Year and Weekdays in Xi’an, China

“…Thus, the BC/CO ratios can indicate the relative contributions of different sources. In addition, region-specific BC/CO values can be used to evaluate the regional emission inventory of BC and CO [40], and it is also an important constraint on global and regional air quality models [41]. Furthermore, the relationship between BC and CO typically changes with time; this is because the atmospheric lifetime of BC is much shorter than that of CO, primarily due to the fact that BC is removed by wet deposition, but CO is not.…”

Black carbon over Mexico: the effect of atmospheric transport on mixing state, mass absorption cross-section, and BC/CO ratios

“…13d) around 19:00 UTC, while the later Yucatan sample (20:34-20:48 UTC) shows depletion in both modes (not shown). Dickerson et al (2002) find a BC/CO ratio of 12.5 ng-BC/µg-CO measured on board the R/V Ronald H. Brown and a BC/CO ratio of 27 ng-BC/µg-CO in the free troposphere as measured on board the C-130 aircraft in 1999 during INDOEX (these values are the slopes, which effectively removes background CO as the intercept), which are both higher than our measurements on the MIRAGE flights. Kondo et al (2006) measured EC/ CO ratios of ∼6 (ng/m 3 )/ppbv (reported at ambient conditions) in Japan, and found this to be at the higher end compared to previouslyreported surface measurements, which ranged from 0.88 in Mexico City (Baumgardner et al, 2002) to 4.1 in Fort Meade, USA (Chen et al, 2001).…”

“…The BC/CO ratio has been suggested as dependent on the source mix, for example, the fraction of heavy-duty diesels in the fleet (Kirchstetter et al, 1999), though other factors like fleet age and condition may also affect the ratio (Baumgardner et al, 2002). BC/CO ratios have also been used to estimate BC emissions based on CO emission inventories (Dickerson et al, 2002). This assumes that both BC and CO are conserved, so that the BC/CO ratio is constant despite atmospheric dilution, and changes in the BC/CO ratio are due to other effects.…”

Characterization of carbonaceous aerosols during the MINOS campaign in Crete, July–August 2001: a multi-analytical approach

“…5 for the first event) but have different slopes, suggesting different biomass burning combustion processes or/with different absorbance properties. Correlations between carbon monoxide (CO) and BC measurements are widely used to characterize different combustion processes (Chen et al, 2001;Dickerson et al, 2002;Baumgardner et al, 2002) and were performed in the field using a fully automated gas chromatograph instrument for CO (Gros et al, 1998a and1998b), and a PSAP for absorbance measurements. As mentioned earlier correlation between BC(IMPROVE) and Abs(PSAP) was excellent all along the duration of the campaign; Abs(PSAP) was used together with CO instead of BC (IMPROVE) in order to provide a better temporal resolution of their ratio.…”