Spatial and temporal variability of open biomass burning in Northeast China from 2003 to 2017

Open biomass burning(OBB)has a significant impact on the heavy haze pollution in Northeast China(NEC)in recent years,which requires the investigation of the spatiotemporal variations of OBB with different vegetation types to better monitor and control OBB in NEC.The MODIS C6 fire and land cover products,together with the emissions inventory from the Global Fire Assimilation System,were used in this study.The changes in the total number of MODIS fire points in NEC from 2003 to 2017 demonstrated a fluctuating but generally rising trend,with a peak during 2013–2017.Most fire points concentrated in two key periods,i.e.March–April(37%)and October–November(46%).The total number of crop residue burnings in March–April was basically slightly fluctuating and increased sharply from 2013,whilst the number in October–November had a fluctuating and upward trend until 2015,when a decline appeared.The amount of OBB in March–April was higher than that in October–November during 2016–17.OBB in Heilongjiang Province comprised a major proportion of all fires,which accounted for 70.7%from 2003 to 2017;however,the proportion was only 66.2%during 2013–2017.The largest proportion of all fires was in cropland(90.8%),then forest(5.3%)and grassland(3.1%).The cumulative emissions of fine particulate matter,nitrogen oxides,and ammonia from agricultural open burning in NEC reached 78.43 Gg,24.9 Gg,and 13.7 Gg for March–April during 2013–17,respectively,which were close to those in October–November.

Local PM_(10) and PM_(2.5) emission inventories from agricultural tillage and harvest in northeastern China

Mineral particles or particulate matters（PMs） emitted during agricultural activities are major recurring sources of atmospheric aerosol loading.However,precise PM inventory from agricultural tillage and harvest in agricultural regions is challenged by infrequent local emission factor（EF） measurements.To understand PM emissions from these practices in northeastern China,we measured EFs of PM_（10） and PM_（2.5） from three field operations（i.e.,tilling,planting and harvesting） in major crop production（i.e.,corn and soybean）,using portable real-time PM analyzers and weather station data.County-level PM_（10） and PM_（2.5） emissions from agricultural tillage and harvest were estimated,based on local EFs,crop areas and crop calendars.The EFs averaged（107 ± 27）,（17 ± 5） and 26 mg/m^2 for field tilling,planting and harvesting under relatively dry conditions（i.e.,soil moisture 〈15%）,respectively.The EFs of PM from field tillage and planting operations were negatively affected by topsoil moisture.The magnitude of PM_（10） and PM_（2.5） emissions from these three activities were estimated to be 35.1 and 9.8 kilotons/yr in northeastern China,respectively,of which Heilongjiang Province accounted for approximately45%.Spatiotemporal distribution showed that most PM_（10） emission occurred in April,May and October and were concentrated in the central regions of the northeastern plain,which is dominated by dryland crops.Further work is needed to estimate the contribution of agricultural dust emissions to regional air quality in northeastern China.

Particle size distribution and characteristics of polycyclic aromatic hydrocarbons during a heavy haze episode in Nanjing,China

A heavy haze episode caused by agricultural burning occurred in Nanjing from November 7 to November 8, 2009. PM10 samples were collected on normal and hazy days from November I to November 14, 2009 at both city and suburban sites of Nanjing. Sixteen PAHs were measured during the day and at night. The results show that the concentrations of the particles were as high as 579.55 and 573.43 μg/m^3 during the haze episode at the city and suburban sites, respectively, 3-4 times higher than those on a normal day. The proportions of fine particles during the haze episode were also higher than those on a normal day. The changes in the concentrations of PAHs were in accordance with the concentrations of the particles. High- molecular-weight PAHs composed approximately 80% of the total PAHs on normal days and during the haze episode. The concentration of PAHs in fine fractions significantly increased during the haze episode, and this increase was most obvious at night at the city site, The proportion of total carcinogenic PAHs in fine particles was relatively high during the haze episode at both sampling sites, particularly at night at the city site.

Typical atmospheric haze during crop harvest season in northeastern China：A case in the Changchun region

This study presents the mass concentrations of PM（2.5）,O3,SO2 and NOxat one urban,one suburban and two rural locations in the Changchun region from September 25 to October 272013. Major chemical components of PM（2.5）at the four sites were daily sampled and analyzed. Most of daily concentrations of SO2（7–82 μg/m^3）,O3（27–171 μg/m^3） and NOx（14–213 μg/m^3） were below the limits of the National Ambient Air Quality Standard（NAAQS）in China. However,PM（2.5）concentrations（143–168 μg/m^3） were 2-fold higher than NAAQS.Higher PM（2.5）concentrations（~ 150 μg/m^3） were measured during the pre-harvest and harvest at the urban site,while PM（2.5）concentrations significantly increased from 250 to400 μg m^（-3） at suburban and rural sites with widespread biomass burning. At all sites,PM（2.5）components were dominated by organic carbon（OC） and followed by soluble component sulfate（SO4^（2-））,ammonium（NH4~＋） and nitrate（NO3^-）. Compared with rural sites,urban site had a higher mineral contribution and lower potassium（K~＋and K） contribution to PM（2.5）.Severe atmospheric haze events that occurred from October 21 to 23 were attributed to strong source emissions（e.g.,biomass burning） and unfavorable air diffusion conditions.Furthermore,coal burning originating from winter heating supply beginning on October 18 increased the atmospheric pollutant emissions. For entire crop harvest period,the Positive Matrix Factorization（PMF） analysis indicated five important emission contributors in the Changchun region,as follows： secondary aerosol（39%）,biomass burning（20%）,supply heating（18%）,soil/road dust（14%） and traffic（9%）.