AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Episodic Ambient PM2.5 in Beijing and Delhi
JOSHUA APTE, Shahzad Gani, Douw Steyn, S.N. Tripathi, University of Texas at Austin
Abstract Number: 580 Working Group: Urban Aerosols
Abstract Very high levels of ambient PM$_(2.5) in Beijing, China and Delhi, India have attracted widespread media attention. We employ publicly available ambient monitoring datasets to compare the magnitude and temporal variability of PM$_(2.5) episodes in these two megacities. For the period from January 2013 – January 2015, arithmetic mean (10th – 90th percentile) hourly PM$_(2.5) levels in Beijing and Delhi were respectively 99 (13-230) and 140 (39-290) micro-g m$^(-3). Winter pollution concentrations in both cities substantially exceed summertime levels. However, winters in Delhi are especially striking for sustained, extreme PM$_(2.5) levels: mean (p10-p90) hourly concentrations are ~220 (90-380) micro-g m$^(-3) for the months of November-January. Episodic winter PM$_(2.5) in Beijing reaches similar peaks, although most frequently during a shorter period in January-February, with concentrations of 150 (14-360) micro-g m$^(-3) in those months. In contrast to Delhi, occasional conditions of low-to-moderate PM$_(2.5) levels are common in Beijing. The monthly 10th percentile of daily-averaged PM$_(2.5) ranged between 14-36 micro-g m$^(-3) for Beijing, compared with 32-160 micro-g m$^(-3) in Delhi. For the two-year period analyzed here, 85 days in Beijing had 24h average PM$_(2.5) levels below the World Health Organization guideline concentration of 25 micro-g m$^(-3), in contrast with only 3 such days in Delhi. Regional-scale meteorological patterns and shifts in wind direction may explain these cleaner conditions in Beijing. Large diurnal variability in ambient PM$_(2.5) concentrations is typical of both cities, which may indicate that locally-emitted primary PM$_(2.5) or locally-formed secondary PM$_(2.5) contribute a high fraction of total PM$_(2.5) concentrations.